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Characteristics of estrous cycles in gilts treated with gonadotropins after estrus or treatment with a progestogen
Accepted Manuscript Characteristics of estrous cycles in gilts treated with gonadotropins after estrus or treatment with a progestogen Mark J. Estienne, Russell J. Crawford PII:
S0093-691X(14)00133-2
DOI:
10.1016/j.theriogenology.2014.03.004
Reference:
THE 12744
To appear in:
Theriogenology
Received Date: 12 August 2013 Revised Date:
14 February 2014
Accepted Date: 1 March 2014
Please cite this article as: Estienne MJ, Crawford RJ, Characteristics of estrous cycles in gilts treated with gonadotropins after estrus or treatment with a progestogen, Theriogenology (2014), doi: 10.1016/ j.theriogenology.2014.03.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Characteristics of estrous cycles in gilts treated with gonadotropins after estrus or
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treatment with a progestogen
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Mark J. Estienne∗ and Russell J. Crawford
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Virginia Tech- Tidewater Agricultural Research and Extension Center, Suffolk, VA, USA
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Abstract
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A combination of eCG (400 IU) and hCG (200 IU) (P.G. 600®, Merck Animal Health, Summit,
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NJ, USA) stimulates puberty in gilts, but variation in the estrual response exists among farms.
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We hypothesized that some of the variability is a consequence of gilts that have commenced
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cycling being inadvertently treated. The objective of Experiment 1 was to determine the effect
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of im P.G. 600 on estrous cycles in sexually mature gilts. Gilts in Treatment 1 (n = 16) received
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P.G. 600 at the onset of daily boar exposure. Gilts in Treatments 2 through 5 (n = 16/treatment)
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were allowed to express a natural first estrus and were then treated with P.G. 600 during the first
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estrous cycle as follows: Treatment 2, at Day 6, Treatment 3 at Day 12, and Treatment 4 at Day
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18 of the estrous cycle. Treatment 5 gilts received no P.G. 600. The proportion of gilts
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displaying a normal estrous cycle (18 to 24 d) was greater (P < 0.05) for Treatments 4 (100%)
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and 5 (100%) compared to Treatments 1 (73.3%) and 3 (60%), with Treatment 2 having a value
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(87.5%) that was not different from the other groups. For Treatment 3, 33% of gilts displayed an
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increased inter-estrus interval that averaged 32.5 d. Concentrations of progesterone remained
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elevated 20 d after the onset of first estrus in Treatment 3 gilts, which supports the concept that
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P.G. 600 administered at Day 12 of the estrous cycle induced follicular growth, ovulation, and
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Correspondence: Tel.: +1 757 657 6450; fax: +1 757 657 9333. E-mail address: [email protected] (M. Estienne)
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formation of corpora lutea that functioned for approximately 15 d, increasing the length of the
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estrous cycle. It is common for swine producers to have groups of replacement gilts that include
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both cycling and prepubertal animals, or individuals, the cycling status of which is unknown.
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The objective of Experiment 2 was to evaluate a system employing a combination of a
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progestogen (MatrixTM, Merck Animal Health) and P.G. 600 to synchronize estrus in
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replacement gilts. Crossbred gilts assumed to be a mix of cycling and prepubertal females, were
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allocated to one of four treatments (n = 12/treatment): Treatment 1, Matrix (15 mg/d) fed for 14
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d and im P.G. 600 24 h after the last feeding of Matrix; Treatment 2, Matrix for 7 d and P.G.
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600; Treatment 3, P.G. 600 only; and Treatment 4, im water only. The percentage of gilts in
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estrus within 7 d after im treatment was greatest (P < 0.02) and days to estrus least (P < 0.05) for
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gilts receiving Matrix for 14 d and P.G. 600 (Treatment 1, 91.7% and 5.4 + 1.9 d; Treatment 2,
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50% and 9.2 + 2.0 d; Treatment 3, 33% and 13.8 + 2.1 d; and, Treatment 4, 50% and 9.1 + 1.9
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d). The results of these experiments suggest that P.G. 600 administered to gilts that have already
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obtained puberty may cause abnormal estrous cycles and demonstrate to swine producers the
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need to correctly classify replacement gilts as prepubertal or cycling before administering the
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product. The use of Matrix and P.G. 600 in combination has potential as an effective strategy for
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synchronizing estrus in a mix of prepubertal and mature, cycling gilts.
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Key Words:
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1.
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Gilt, estrus, progestogen, gonadotropin
Introduction
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In some experiments, im treatment with a commercially available combination of eCG (400
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IU) and hCG (200 IU) (P.G. 600®; Merck Animal Health, Summit, NJ, USA) effectively
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advanced the onset of puberty in gilts. For example, Garcia et al. [1] reported that 83% of gilts
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treated with P.G. 600 displayed estrus within 7 d and of the gilts responding to the gonadotropin
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product, 97.1% subsequently displayed a second and 94.3% a third, estrus at approximately 21-d
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intervals. However, Britt et al. [2] reported lower overall response rates to P.G. 600 on ten
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commercial farms with 55% and 73% of treated gilts displaying estrus by 7 and 28 d post-
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treatment, respectively. Moreover, among farms, the percentage of P.G. 600-treated gilts in
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estrus within 28 d ranged from 42 to 97%.
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Neill and Day [3] first demonstrated that ovulation and formation of corpora lutea (CL)
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could be induced during the luteal phase of the porcine estrous cycle and that the original CL and
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the induced CL possessed their own inherent life spans. Specifically, the researchers showed
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that induced CL were formed by giving eCG on Day 5 or 6 of the estrous cycle, followed 72 to
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96 h later with hCG.
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Although the spontaneous CL from the original ovulation regressed on approximately Day 15 to
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16, the induced CL also functioned for a normal period of 15 to 16 d, thereby increasing the
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inter-estrus interval.
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Ovulation occurred on approximately Day 11 of the estrous cycle.
It is not known if P.G. 600, given during the luteal phase, also induces ovulation and the
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formation of accessory CL. We hypothesized that some of the variation in overall response to
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P.G. 600 exhibited among farms [2] is due to at least some pubertal and thus, cycling gilts being
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inadvertently treated. Moreover, depending on the day of the estrous cycle when treated, these
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individuals may or may not exhibit estrus within 7 d post-injection and in some cases the
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induction of accessory CL may cause an extended inter-estrus interval. Therefore, the objective
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of Experiment 1 was to determine the effects of P.G. 600, administered at various days of the
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estrous cycle, on the onset of estrus and estrous cycles in gilts. Producers inevitably receive
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groups of replacement gilts comprised of a mix of both prepubertal and cycling animals. Thus,
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in Experiment 2, we evaluated a system employing a combination of both an orally active
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progestogen (MatrixTM; Merck Animal Health) and P.G. 600 that could be used to synchronize
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estrus in such a heterogeneous group of gilts.
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2.
Materials and methods
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2.1 Animals and housing
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The experiments were conducted at the Virginia Tech-Tidewater Agricultural Research and
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Extension Center in Suffolk, VA, USA, and protocols were reviewed and approved by the
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Institutional Animal Care and Use Committee at Virginia Tech.
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Yorkshire x Landrace sows mated to Duroc boars. Gilts from this genetic base tend to be later-
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maturing and in another experiment conducted simultaneously to those reported here, average
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age at puberty in gilts receiving daily boar exposure (n = 36) was 199.1 d (SD = 15.2) (Estienne,
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unpublished data).
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expressed puberty by 240 d of age.
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Gilts were farrowed by
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Moreover, in another report [4], approximately 10% of gilts had not
The animals were housed in a breeding-gestation barn in pens measuring 5.18 x 2.74 m
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(Experiment 1) or in a grow-finish barn in pens measuring 1.83 x 3.05 m (Experiment 2). Pens
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were situated over a combination of solid and slatted concrete floors and each pen contained a
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nipple waterer. Gilts were floor-fed daily 2.7 kg of a fortified corn and soybean meal-based diet
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that met or exceeded recommendations for the various nutrients [5].
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2.2 Experiment 1: Effect of P.G. 600 on estrous cycles
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A total of 80 gilts, 110 + 3.4 kg body weight (mean + SE) and 175 + 0.4 d of age, were
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housed in eight pens (n = 10 gilts per pen). Throughout the experiment, gilts were checked daily
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for standing estrus in full contact with a mature boar [6]. Gilts in Treatment 1 (n = 16) received
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P.G. 600 (5 mL im behind the ear in the neck muscle; 18 gauge, 3.81 cm length needle; Air-Tite
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Products Co., Inc., Virginia Beach, VA, USA) at the onset of daily boar exposure. Gilts in
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Treatments 2 through 5 were allowed to express a natural first estrus and were then treated as
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follows (n = 16/treatment): Treatment 2, P.G. 600 administered at Day 6 of the first estrous
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cycle; Treatment 3, P.G. 600 administered at Day 12 of the first estrous cycle; Treatment 4, P.G.
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600 administered at Day 18 of the first estrous cycle; and Treatment 5, no P.G. 600 administered.
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Each of the eight pens contained two gilts from each treatment group. Beginning at Day 0 of the
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first estrous cycle (first day of standing estrus), blood samples were collected at 10-d intervals
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until up to Day 70 after the onset of first estrus.
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2.3 Experiment 2: Using Matrix and P.G. 600 in combination to synchronize estrus
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A total of 48 gilts, 143 + 3.0 kg body weight and 246 + 0.4 d of age and assumed to be a mix of
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both cycling and prepubertal females were used. Gilts were housed in pens of 4 gilts each and
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each of the 12 pens contained one gilt from each of four treatments: Treatment 1, Matrix (15 mg)
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fed daily for 14 d and im P.G. 600 24 h after the last feeding of Matrix; Treatment 2, Matrix fed
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daily for 7 d and P.G. 600 24 h after last feeding of Matrix; Treatment 3, P.G. 600 only; and
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Treatment 4, 5 mL im water only (n = 12 gilts per treatment). Feeding of Matrix was staggered
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so that among all four treatments, injections of P.G. 600 or water occurred on the same day.
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Gilts were checked daily for standing estrus in full contact with a mature boar and were mated
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using AI, 0 and 24 h after onset of estrus. Semen was obtained from a commercial source
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(Swine Genetics International, Inc., Cambridge, IA, USA) and each dose contained a minimum
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of 6 billion spermatozoa. Gilts were checked for estrus daily for 37 d after injection of P.G. 600
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and onset of daily boar exposure.
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2.4 Blood collection and radioimmunoassay Gilts were restrained with a metal hog snare and blood samples (10 mL) were collected via
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jugular venipuncture using a 7.62 cm length, 16 gauge needle (Air-Tite Products Co., Inc.).
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Blood was allowed to clot overnight at 4˚C and was then centrifuged and serum harvested.
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Serum
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radioimmunoassay [7]. The intra-assay CV was 1.0% and assay sensitivity was 0.02 ng/mL of
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serum.
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2.5 Statistical analyses
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progesterone
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Data were analyzed using SAS (SAS Institute, Inc., Cary, NC, USA). For Experiment 1,
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the percentage of gilts in estrus after P.G. 600 and the onset of boar exposure (Treatment 1) and
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boar exposure alone (Treatments 2 through 5 combined) and the percentages of gilts with normal
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(18 to 24 d; [6]) or abnormal (< 18 d or > 24 d) estrous cycle lengths in each of the five
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treatments were subjected to chi-squares analyses. Treatment to estrus intervals, and age at
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puberty were subjected to ANOVA for a randomized block design using the GLM procedure of
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SAS. The model included treatment as the main effect and pen as the blocking variable. Serum
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progesterone concentrations were analyzed using ANOVA for repeated measures with a model
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that included treatment, gilt within treatment, day and the treatment by day interaction as
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possible sources of variation. Treatment was tested using gilt within treatment as the error term
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and day was tested against treatment by day.
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For Experiment 2, the effect of treatment on the percentage of gilts in estrus by Day 7, Day
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10, or Day 28 was evaluated using chi-squares analyses. Treatment to estrus interval, the length
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of estrus, and farrowing characteristics were evaluated using ANOVA with a model that included
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treatment and pen as possible sources of variation. Gilt body weight at the time of P.G. 600 or
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water treatment was used as a covariate. For both experiments, individual means were compared
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using the PDIFF option of the GLM procedure of SAS.
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3.
Results and Discussion:
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Experiment 1: Effect of P.G. 600 on estrous cycles
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Shown in Table 1 are the effects of P.G. 600 on puberty. Consistent with previous reports
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[2,8], P.G. 600 increased (P < 0.05) the percentage of gilts in estrus within 7 d after treatment
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and for these individuals, decreased (P < 0.01) the interval to first estrus. The response rate to
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P.G. 600 (43.8% in estrus by Day 7 after treatment), however, was less than in previous studies
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conducted in our laboratory. For example, Garcia et al. [1] treated gilts that were 180 d of age
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with P.G. 600, and within 7 d, 83% (35/42) of the treated animals displayed estrus. Although the
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dichotomy in response rates is not readily explained it could be a consequence of the relatively
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small number of animals treated in the current study, or a genetic component could be involved.
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In our previous work [1], prolific, maternal-line Yorkshire x Landrace gilts were used, however
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in the current study gilts were farrowed by Yorkshire x Landrace sows mated to terminal Duroc
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boars. Consistent with this hypothesis, Tilton et al. [9] reported that gilts selected to reach
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puberty at a younger age responded more favorably to exogenous treatment with gonadotropins
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than did gilts from a relaxed selection line.
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In the experiment reported here, there was no effect (P = 0.57) of P.G. 600 on the
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percentage of approximately 175 d-old gilts expressing puberty within 28 d after treatment and
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the start of daily boar exposure (table 1), suggesting that P.G. 600 probably did not induce a
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“silent” first estrus followed by standing estrus approximately 21 d later. This is in contrast to
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work by Britt et al. [2] who showed a positive effect of P.G. 600 on the percentage of gilts (165
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to 225 d of age) exhibiting estrus within 28 d after the start of daily estrus detection. Overall,
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there were no differences (P > 0.28) between groups for the percentage of gilts that were
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pubertal by the end of the experiment, age at puberty, or the interval from the start of daily estrus
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detection to first estrus (table 1).
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Effects of P.G. 600 on estrous cycles are summarized in Table 2. The percentage of gilts
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displaying normal estrous cycles was greater (P < 0.05) in gilts not administered P.G. 600 or that
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were administered P.G. 600 at Day 18 of the estrous cycle, compared with gilts administered
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P.G. 600 at the onset of daily detection of estrus or administered P.G. 600 at Day 12 of the
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estrous cycle, with gilts administered P.G. 600 at Day 6 of the estrous cycle having an
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intermediate value that was not different (P > 0.05) from the other groups. For these normally
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cycling gilts, the length of estrous cycles was greatest (P < 0.05) in gilts administered P.G. 600 at
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the start of the experiment and least (P < 0.05) for gilts that received no P.G. 600. Although a
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biological explanation for that difference among treatments remains to be determined, it could
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reflect differences in ovulation rate and consequently, circulating progesterone concentrations.
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Gilts selected for high ovulation rates had greater concentrations of progesterone and estrous
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cycle lengths compared to gilts from a random selection line exhibiting low ovulation rates [10].
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Accordingly, increased ovulation rates and circulating concentrations of progesterone in gilts
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treated with P.G. 600 have been reported [7,11]. Although ovulation rates were not determined
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in the current study, gilts treated with P.G. 600 at the start of the experiment and classified as
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exhibiting estrous cycles of normal lengths had the greatest estrous cycle length and as discussed
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below, greater concentrations of progesterone at Day 10 of the estrous cycle compared to gilts
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given P.G. 600 at Day 12 or 18 of the estrous cycle or gilts not receiving gonadotropins.
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The percentage of gilts displaying abnormal estrous cycle lengths was greater (P < 0.05;
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table 1) for gilts receiving P.G. 600 at the initiation of daily boar exposure and detection of estrus
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or at Day 12 of the estrous cycle, compared with gilts receiving P.G. 600 at Day 18 of the estrous
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cycle or that received no P.G. 600; Gilts administered P.G. 600 at Day 6 of the estrous cycle had
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an intermediate value that was not different (P > 0.05) from the other groups. The length of
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estrous cycles in gilts exhibiting abnormal estrous cycles was variable and not different (P =
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0.75) among groups.
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Progesterone concentrations in serum of gilts was affected by a treatment by day interaction (P = 0.03) as shown in Figure 1.
At the onset of standing estrus (Day 0),
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concentrations of progesterone were minimal and not different among groups (P > 0.05). At Day
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10 of estrous cycles, progesterone concentrations were greater (P < 0.05) for gilts receiving P.G.
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600 at the onset of the study or at Day 6 of the estrous cycle compared with the other three
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groups. At Day 20, serum progesterone concentrations were greatest (P < 0.05) for gilts that
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received P.G. 600 at Day 12 of the cycle and least (P < 0.05) for gilts receiving no P.G. 600.
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Figure 2 shows progesterone concentrations in serum of gilts that received P.G. 600 at Day
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12 of the cycle and that exhibited either normal (n = 9; 20.2 + 0.41 d) or abnormal (n = 5; 32.5 +
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0.41 d) estrous cycle lengths. There was an interaction of cycle type (normal versus abnormal
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length) and day (P = 0.03) on progesterone concentrations in serum.
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600 on Day 12 and that showed an abnormally long inter-estrus interval had greater
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concentrations of progesterone on Day 20 compared to gilts administered P.G. 600 on Day 12 of
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the estrous cycle and that displayed normal estrous cycle lengths. It is well-established that
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accessory CL can be induced in luteal-phase gilts using eCG followed 72 to 96 h later with hCG
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[3, 12], and as a consequence, extend the luteal phase of the estrous cycle. Our findings that
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Gilts administered P.G.
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serum progesterone concentrations remained elevated at Day 20 of the estrous cycle in 33% (5 of
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15) of the gilts administered P.G. 600 on Day 12, and that the inter-estrus interval in these
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animals was approximately 33 d suggests that the gilts ovulated mid-cycle and returned to estrus
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only after regression of the induced CL. These results are consistent with the notion that P.G.
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600, administered in the mid-luteal phase of the estrous cycle may extend the inter-estrus interval
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in gilts.
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producers the need to correctly classify replacement gilts as prepubertal or cycling before
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administering P.G. 600, and illustrate a physiological basis for at least some gilts not responding
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to the compound by displaying estrus within 7 d post-treatment.
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Experiment 2: Use of Matrix and P.G. 600 in combination to synchronize estrus in replacement
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gilts
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From a practical standpoint, the results of this experiment demonstrate to swine
For experiment 2, gilts were assumed to be a mix of cycling and prepubertal individuals,
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although the percentages of each were not ascertained beforehand. As mentioned previously,
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gilts from the genetic base employed here tend to be later-maturing (age at puberty of
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approximately 200 d of age). Moreover, in Experiment 2 boar exposure did not commence until
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after treatment with Matrix and/or P.G. 600.
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Shown in Table 3 are characteristics of estrus for gilts treated with Matrix and/or P.G. 600
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and gilts receiving no exogenous hormones. The percentage of gilts in estrus within 7 d after
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injections was greatest (P < 0.05) and days to estrus least (P < 0.05) for gilts receiving Matrix for
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14 d and P.G. 600 24 h after the last feeding of Matrix. It is not surprising that the percentage of
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gilts in estrus soon after treatment with P.G. 600 alone was low because gilts were purposefully
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treated at an age and weight at which in all likelihood there would have been some gilts already
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cycling. Based on the results of Experiment 1, it is possible that some cycling gilts were treated
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with P.G. 600 mid-cycle, and as a consequence, had an extended luteal phase and a greater inter-
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estrus interval. Consistent with this concept, the days to estrus was greatest (P < 0.05) for gilts
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treated with P.G. 600 alone. The results of this experiment are consistent with previous work from our laboratory
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[7,11,13] and demonstrate that a combination of Matrix, given for 14 or 18 d, and P.G. 600,
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administered 24 h after the last feeding of Matrix, effectively synchronize estrus in gilts. In
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commercial swine operations, it is inevitable that at least occasionally producers will have
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groups of gilts that include both cycling and prepubertal animals, or have groups of replacement
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gilts, the cycling status of which is unknown. We suggest that in those situations, use of a
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combination of Matrix and P.G. 600 is indicated. Indeed, efficacy of this system has been
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demonstrated in commercial settings. On a 100-sow independent operation, 17 gilts were fed
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Matrix for 14 d and treated with P.G. 600 24 h after withdrawal of Matrix; Over 94% of gilts
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were in standing estrus by Day 7 after the last feeding of Matrix [14]. On a 1,000-sow company
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farm, 240 gilts were similarly treated with the combination of Matrix and P.G. 600 and 86.2% of
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gilts were in standing estrus by Day 10 after the last feeding of Matrix (average of 6.4 d from
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Matrix withdrawal to estrus) and conception rate was 85.5% [15]. In that study [15], analysis of
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serum concentrations of progesterone in blood samples collected before treatment indicated that
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26% of the gilts were cycling before Matrix.
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performance between gilts that were cycling and gilts that were prepubertal when feeding of
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Matrix commenced [15].
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There were no differences in reproductive
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In previous studies, gilts that received P.G. 600 after Matrix withdrawal had significantly
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greater ovulation rates than did gilts that received Matrix alone [7,11] and prepubertal gilts
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pretreated with Matrix for 18 d had a numerical, but statistically non-significant increase in
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ovulation rate in response to P.G. 600 compared with prepubertal gilts that received P.G. 600
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only (16.6 vs. 14.4) [7]. The current experiment employed an insufficient number of animals to
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allow firm conclusions regarding effects of Matrix and P.G. 600 in combination on farrowing
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performance, and there were no effects of treatment on total litter size or number born alive
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(table 4). However, total litter size was 12.0, 11.3, 10.1, and 8.9 for gilts receiving Matrix for 14
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d and P.G. 600, Matrix for 7 d and P.G. 600, P.G. 600 only, and no exogenous hormones,
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respectively. Consistent with the numerically greatest litter size, average pig birth weight was
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least for gilts receiving Matrix for 14 d and P.G. 600 (table 4).
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In summary and based on our data, P.G. 600 administered to sexually mature gilts at mid-
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cycle (Day 12) may cause follicular growth, ovulation and formation of induced corpora lutea,
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and may lengthen the inter-estrus interval in approximately 33 percent of animals. Thus, some
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variability in response rates to P.G. 600 among farms may be attributed to producers
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unknowingly treating gilts that are already pubertal and therefore cycling.
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Experiment 2 indicate that Matrix fed for 14 d followed by treatment with P.G. 600 24 h after the
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last feeding of Matrix is an effective system for stimulating and synchronizing estrus in groups
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of gilts that include both cycling and prepubertal animals, or in groups of replacement gilts, the
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cycling status of which is unknown.
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commercial settings using different genetic sources (for example, more prolific, maternal-line
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stock).
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economic viability.
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The results of
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However, this concept needs to be further-tested in
Finally, the system described here must be subjected to an analysis to determine
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Acknowledgements Financial support for this research was provided by the Virginia Pork Industry Board
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(Richmond, VA, USA) and Merck Animal Health (Summit, NJ, USA). The authors thank Terry
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Lee and Lee Johnson for technical assistance.
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References
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Garcia A, Estienne MJ, Harper AF, Knight JW. Failure of gonadotropin therapy to induce estrus in gilts treated with a GnRH analog to suppress ovarian activity. Intern J
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Britt JH, Day BN, Webel SK, Brauer MA. Induction of fertile estrus in prepuberal gilts
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chorionic gonadotropin. J Anim Sci 1989;67:1148-53. [3]
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Neill JD, Day BN. Relationship of developmental stage to regression of the corpus
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NRC. Nutrient Requirements of Swine. 11th Revised ed. Natl Acad Press, Washington
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Belstra B, Flowers B, See MT, Singleton W. Detection of estrus or heat. Pork
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Information Gateway 2001;Fact Sheet No. 08-01-01. Available at:
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[7]
Estienne MJ, Harper AF, Horsley BR, Estienne CE, Knight JW. Effects of P.G. 600 on
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the onset of estrus and ovulation rate in gilts treated with Regu-mate. J Anim Sci
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2001;79:2757-61. [8]
Knox RV, Tudor KW, Rodriguez-Zas SL, Robb JA.
Effect of subcutaneous vs.
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intramuscular administration of P.G. 600 on estrual and ovulatory responses of
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prepubertal gilts. J Anim Sci 2000;78:1732-37.
Evaluation of response to hormonal therapy in
prepubertal gilts of different genetic lines. J Anim Sci 1995;73:3062-68.
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Tilton SL, Bates RO, Prather RS.
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[10]
Knox RV, Vatzias G, Naber CH, Zimmerman DR. Plasma gonadotropins and ovarian
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hormones during the estrous cycle in high compared to low ovulation rate gilts. J Anim
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Sci 2003;81:249-60.
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[11]
Horsley BR, Estienne MJ, Harper AF, Purcell SH, Baitis HK, Beal WE, Knight JW. Effect of P.G. 600 on the timing of ovulation in gilts treated with altrenogest. J Anim Sci
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2005;83:1690-95.
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[12]
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Rampacek GB, Kraeling RR, Barb CR, Estienne CE, Estienne MJ.
Regression of
induced corpora lutea in mature cyclic gilts by human chorionic gonadotropin. J Anim
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Sci 1992;70:3144-48. [13]
Estienne MJ, Harper AF. Case study: Synchronization of estrus and fertility in gilts
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administered P.G. 600® after treatment with Regu-mate® for 14 or 18 days. The Prof
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Anim Sci 2002;18:158-61.
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[14]
Estienne MJ. Use of MATRIX and P.G. 600 in combination to synchronize estrus in
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replacement gilts. Proceedings of the 2011 Meeting of the Southern Section- American
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Society of Animal Science 2011;31.
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[15]
Alberti KA, Pittman JS, Estienne MJ. Comparison of two gilt synchronization protocols
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using MatrixTM and P.G. 600®. Proceedings of the 2011 Meeting of the American
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Association of Swine Veterinarians 2011;289-90.
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Number of gilts 16 64 Puberty by Day 7 of experiment, (%) 7/16 (43.8) 13/64 (20.3) Age at puberty, d 180.5 181.5 Interval from start of experiment to puberty, d 4.7 6.1 Puberty by Day 28 of experiment, (%) 10/16 (62.5) 36/64 (54.7) Age at puberty, d 186.2 189.7 Interval from start of experiment to puberty, d 10.3 14.5 Puberty by end of experiment, (%) 15/16 (93.8) 63/64 (98.4) Age at puberty, d 201.3 203.5 Interval from start of experiment to puberty, d 25.5 28.3 1 Puberty defined as first occurrence of standing estrus in the presence of a mature boar.
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Table 1. Effect of im treatment with 400 IU eCG and 200 IU hCG (P.G. 600; Merck Animal Health, Summit, NJ, USA) on puberty1 in gilts. P.G. 600 at initiation of experiment Item Yes2 No3 SE P
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2
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Treatment 1.
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Treatments 2 through 5 combined.
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----0.51 0.31 --2.4 2.4 --4.3 4.3
--0.05 0.19 <0.01 0.57 0.17 0.11 0.28 0.64 0.55
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Table 2. Effect of im treatment with 400 IU eCG and 200 IU hCG (P.G. 600; Merck Animal Health, Summit, NJ, USA) on estrous cycles in gilts P.G. 600 administered at:
333 334
Day 6 16 16
Number of gilts assigned Number of gilts displaying first estrus Normal cycles1, (%) 11/15 (73.3a) 14/16 (87.5a,b) Cycle length, d 21.3a 20.6a,b a Abnormal cycles, (%) 3/15 (20.0 ) 2/16 (12.5a,b) Cycle length, d 37.0 23.7 Estrus then anestrus, (%) 1/15 (6.7) 0/16 (0) 1 Normal cycles defined as 18 to 24 d in length. a,b
Day 12 16 15
Day 18 16 16
9/15 (60.0a) 20.2a,b,c 5/15 (33.3a) 32.5 1/15 (6.7)
16/16 (100b) 19.9b,c 0/16 (0b) --0/16 (0)
Within a row, means with different superscripts differ (P < 0.05).
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No P.G. 600 16 16
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Table 3. Characteristics of estrus and estrous cycles in gilts treated with Matrix (Merck Animal Health, Summit, NJ, USA) and/or P.G. 600 (Merck Animal Health) and gilts receiving no exogenous hormones1.
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Matrix 14 d Matrix 7 d P.G. 600 only No Item: + P.G. 600 + P.G. 600 Hormones Number of gilts 12 12 12 12 Percentage of gilts in estrus by Day 7 after P.G. 600 11/12 (91.7a) 6/12 (50.0b) 4/12 (33.3b) 6/12 (50.0b) a b b by Day 10 after P.G. 600 12/12 (100 ) 6/12 (50.0 ) 4/12 (33.3 ) 8/12 (66.6b) a a,b b by Day 28 after P.G. 600 12/12 (100 ) 11/12 (91.7 ) 9/12* (75.0 ) 12/12 (100a) Interval to estrus, d 5.4a 9.2a,b 13.8b 9.1a,b Length of estrus, d 2.03 2.08 1.57 1.90 1 Gilts were checked for estrus daily for 37 d after injection of P.G. 600 and onset of boar exposure.
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*One gilt displayed estrus on Day 31. This gilt is not included in the percentage of gilts displaying estrus.
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a,b
Within a row, means with different superscripts differ (P < 0.05).
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Table 4. Farrowing performance for gilts treated with Matrix (Merck Animal Health, Summit, NJ, USA) and/or P.G. 600 (Merck Animal Health) and gilts receiving no exogenous hormones1. Matrix 14 d Matrix 7 d P.G. 600 only No SE P Item: + P.G. 600 + P.G. 600 Hormones Number of gilts mated 12 11 10 12 ----Gilts farrowing, (%) 7/12 (58.3) 6/11 (54.5) 9/10 (90.0) 11/12 (91.7) --Total Born 12.0 11.3 10.1 8.9 1.9 0.45 Born Live 8.1 11.2 9.0 8.0 1.8 0.53 Pig birth weight, kg 1.41a 1.74a,b 1.93b 1.91b 0.16 0.05 1 With the exception of one gilt in the P.G. 600 only group that was mated on d 31, all gilts were mated within 28 d after P.G. 600 and onset of boar exposure or onset of boar exposure only.
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Figure Legends
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Figure 1. Progesterone concentrations in gilts treated with 400 IU eCG and 200 IU hCG (P.G.
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600; Merck Animal Health, Summit, NJ USA) on various days of the estrous cycle. There was
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an interaction of treatment and day (P = 0.03). Within days, bars with different superscripts
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differ (P < 0.05).
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Figure 2. Progesterone concentrations in gilts treated with 400 IU eCG and 200 IU hCG (P.G.
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600; Merck Animal Health, Summit, NJ, USA) on Day 12 of the estrous cycle and that exhibited
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normal (n = 9; 20.2 + 0.41 d) or abnormal (n = 5; 32.5 + 0.41 d) estrous cycle lengths. There
358
was an interaction of cycle type (normal or abnormal length) and day (P = 0.03) on progesterone
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concentrations. Within days, bars with different superscripts differ (P < 0.05).
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Day relative to onset of estrus
Day of P.G. 600 Start of study Day 6 of cycle Day 12 of cycle Day 18 of cycle None
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S0093-691X(14)00133-2
DOI:
10.1016/j.theriogenology.2014.03.004
Reference:
THE 12744
To appear in:
Theriogenology
Received Date: 12 August 2013 Revised Date:
14 February 2014
Accepted Date: 1 March 2014
Please cite this article as: Estienne MJ, Crawford RJ, Characteristics of estrous cycles in gilts treated with gonadotropins after estrus or treatment with a progestogen, Theriogenology (2014), doi: 10.1016/ j.theriogenology.2014.03.004. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Characteristics of estrous cycles in gilts treated with gonadotropins after estrus or
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treatment with a progestogen
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Mark J. Estienne∗ and Russell J. Crawford
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Virginia Tech- Tidewater Agricultural Research and Extension Center, Suffolk, VA, USA
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Abstract
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A combination of eCG (400 IU) and hCG (200 IU) (P.G. 600®, Merck Animal Health, Summit,
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NJ, USA) stimulates puberty in gilts, but variation in the estrual response exists among farms.
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We hypothesized that some of the variability is a consequence of gilts that have commenced
11
cycling being inadvertently treated. The objective of Experiment 1 was to determine the effect
12
of im P.G. 600 on estrous cycles in sexually mature gilts. Gilts in Treatment 1 (n = 16) received
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P.G. 600 at the onset of daily boar exposure. Gilts in Treatments 2 through 5 (n = 16/treatment)
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were allowed to express a natural first estrus and were then treated with P.G. 600 during the first
15
estrous cycle as follows: Treatment 2, at Day 6, Treatment 3 at Day 12, and Treatment 4 at Day
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18 of the estrous cycle. Treatment 5 gilts received no P.G. 600. The proportion of gilts
17
displaying a normal estrous cycle (18 to 24 d) was greater (P < 0.05) for Treatments 4 (100%)
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and 5 (100%) compared to Treatments 1 (73.3%) and 3 (60%), with Treatment 2 having a value
19
(87.5%) that was not different from the other groups. For Treatment 3, 33% of gilts displayed an
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increased inter-estrus interval that averaged 32.5 d. Concentrations of progesterone remained
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elevated 20 d after the onset of first estrus in Treatment 3 gilts, which supports the concept that
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P.G. 600 administered at Day 12 of the estrous cycle induced follicular growth, ovulation, and
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∗
Correspondence: Tel.: +1 757 657 6450; fax: +1 757 657 9333. E-mail address: [email protected] (M. Estienne)
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formation of corpora lutea that functioned for approximately 15 d, increasing the length of the
24
estrous cycle. It is common for swine producers to have groups of replacement gilts that include
25
both cycling and prepubertal animals, or individuals, the cycling status of which is unknown.
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The objective of Experiment 2 was to evaluate a system employing a combination of a
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progestogen (MatrixTM, Merck Animal Health) and P.G. 600 to synchronize estrus in
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replacement gilts. Crossbred gilts assumed to be a mix of cycling and prepubertal females, were
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allocated to one of four treatments (n = 12/treatment): Treatment 1, Matrix (15 mg/d) fed for 14
30
d and im P.G. 600 24 h after the last feeding of Matrix; Treatment 2, Matrix for 7 d and P.G.
31
600; Treatment 3, P.G. 600 only; and Treatment 4, im water only. The percentage of gilts in
32
estrus within 7 d after im treatment was greatest (P < 0.02) and days to estrus least (P < 0.05) for
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gilts receiving Matrix for 14 d and P.G. 600 (Treatment 1, 91.7% and 5.4 + 1.9 d; Treatment 2,
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50% and 9.2 + 2.0 d; Treatment 3, 33% and 13.8 + 2.1 d; and, Treatment 4, 50% and 9.1 + 1.9
35
d). The results of these experiments suggest that P.G. 600 administered to gilts that have already
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obtained puberty may cause abnormal estrous cycles and demonstrate to swine producers the
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need to correctly classify replacement gilts as prepubertal or cycling before administering the
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product. The use of Matrix and P.G. 600 in combination has potential as an effective strategy for
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synchronizing estrus in a mix of prepubertal and mature, cycling gilts.
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Key Words:
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1.
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Gilt, estrus, progestogen, gonadotropin
Introduction
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In some experiments, im treatment with a commercially available combination of eCG (400
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IU) and hCG (200 IU) (P.G. 600®; Merck Animal Health, Summit, NJ, USA) effectively
44
advanced the onset of puberty in gilts. For example, Garcia et al. [1] reported that 83% of gilts
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treated with P.G. 600 displayed estrus within 7 d and of the gilts responding to the gonadotropin
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product, 97.1% subsequently displayed a second and 94.3% a third, estrus at approximately 21-d
47
intervals. However, Britt et al. [2] reported lower overall response rates to P.G. 600 on ten
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commercial farms with 55% and 73% of treated gilts displaying estrus by 7 and 28 d post-
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treatment, respectively. Moreover, among farms, the percentage of P.G. 600-treated gilts in
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estrus within 28 d ranged from 42 to 97%.
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Neill and Day [3] first demonstrated that ovulation and formation of corpora lutea (CL)
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could be induced during the luteal phase of the porcine estrous cycle and that the original CL and
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the induced CL possessed their own inherent life spans. Specifically, the researchers showed
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that induced CL were formed by giving eCG on Day 5 or 6 of the estrous cycle, followed 72 to
55
96 h later with hCG.
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Although the spontaneous CL from the original ovulation regressed on approximately Day 15 to
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16, the induced CL also functioned for a normal period of 15 to 16 d, thereby increasing the
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inter-estrus interval.
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It is not known if P.G. 600, given during the luteal phase, also induces ovulation and the
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formation of accessory CL. We hypothesized that some of the variation in overall response to
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P.G. 600 exhibited among farms [2] is due to at least some pubertal and thus, cycling gilts being
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inadvertently treated. Moreover, depending on the day of the estrous cycle when treated, these
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individuals may or may not exhibit estrus within 7 d post-injection and in some cases the
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induction of accessory CL may cause an extended inter-estrus interval. Therefore, the objective
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of Experiment 1 was to determine the effects of P.G. 600, administered at various days of the
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estrous cycle, on the onset of estrus and estrous cycles in gilts. Producers inevitably receive
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groups of replacement gilts comprised of a mix of both prepubertal and cycling animals. Thus,
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in Experiment 2, we evaluated a system employing a combination of both an orally active
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progestogen (MatrixTM; Merck Animal Health) and P.G. 600 that could be used to synchronize
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estrus in such a heterogeneous group of gilts.
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2.
Materials and methods
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2.1 Animals and housing
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The experiments were conducted at the Virginia Tech-Tidewater Agricultural Research and
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Extension Center in Suffolk, VA, USA, and protocols were reviewed and approved by the
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Institutional Animal Care and Use Committee at Virginia Tech.
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Yorkshire x Landrace sows mated to Duroc boars. Gilts from this genetic base tend to be later-
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maturing and in another experiment conducted simultaneously to those reported here, average
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age at puberty in gilts receiving daily boar exposure (n = 36) was 199.1 d (SD = 15.2) (Estienne,
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unpublished data).
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expressed puberty by 240 d of age.
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The animals were housed in a breeding-gestation barn in pens measuring 5.18 x 2.74 m
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(Experiment 1) or in a grow-finish barn in pens measuring 1.83 x 3.05 m (Experiment 2). Pens
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were situated over a combination of solid and slatted concrete floors and each pen contained a
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nipple waterer. Gilts were floor-fed daily 2.7 kg of a fortified corn and soybean meal-based diet
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that met or exceeded recommendations for the various nutrients [5].
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2.2 Experiment 1: Effect of P.G. 600 on estrous cycles
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A total of 80 gilts, 110 + 3.4 kg body weight (mean + SE) and 175 + 0.4 d of age, were
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housed in eight pens (n = 10 gilts per pen). Throughout the experiment, gilts were checked daily
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for standing estrus in full contact with a mature boar [6]. Gilts in Treatment 1 (n = 16) received
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P.G. 600 (5 mL im behind the ear in the neck muscle; 18 gauge, 3.81 cm length needle; Air-Tite
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Products Co., Inc., Virginia Beach, VA, USA) at the onset of daily boar exposure. Gilts in
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Treatments 2 through 5 were allowed to express a natural first estrus and were then treated as
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follows (n = 16/treatment): Treatment 2, P.G. 600 administered at Day 6 of the first estrous
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cycle; Treatment 3, P.G. 600 administered at Day 12 of the first estrous cycle; Treatment 4, P.G.
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600 administered at Day 18 of the first estrous cycle; and Treatment 5, no P.G. 600 administered.
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Each of the eight pens contained two gilts from each treatment group. Beginning at Day 0 of the
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first estrous cycle (first day of standing estrus), blood samples were collected at 10-d intervals
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until up to Day 70 after the onset of first estrus.
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2.3 Experiment 2: Using Matrix and P.G. 600 in combination to synchronize estrus
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A total of 48 gilts, 143 + 3.0 kg body weight and 246 + 0.4 d of age and assumed to be a mix of
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both cycling and prepubertal females were used. Gilts were housed in pens of 4 gilts each and
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each of the 12 pens contained one gilt from each of four treatments: Treatment 1, Matrix (15 mg)
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fed daily for 14 d and im P.G. 600 24 h after the last feeding of Matrix; Treatment 2, Matrix fed
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daily for 7 d and P.G. 600 24 h after last feeding of Matrix; Treatment 3, P.G. 600 only; and
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Treatment 4, 5 mL im water only (n = 12 gilts per treatment). Feeding of Matrix was staggered
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so that among all four treatments, injections of P.G. 600 or water occurred on the same day.
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Gilts were checked daily for standing estrus in full contact with a mature boar and were mated
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using AI, 0 and 24 h after onset of estrus. Semen was obtained from a commercial source
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(Swine Genetics International, Inc., Cambridge, IA, USA) and each dose contained a minimum
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of 6 billion spermatozoa. Gilts were checked for estrus daily for 37 d after injection of P.G. 600
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and onset of daily boar exposure.
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2.4 Blood collection and radioimmunoassay Gilts were restrained with a metal hog snare and blood samples (10 mL) were collected via
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jugular venipuncture using a 7.62 cm length, 16 gauge needle (Air-Tite Products Co., Inc.).
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Blood was allowed to clot overnight at 4˚C and was then centrifuged and serum harvested.
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Serum
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radioimmunoassay [7]. The intra-assay CV was 1.0% and assay sensitivity was 0.02 ng/mL of
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serum.
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2.5 Statistical analyses
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Data were analyzed using SAS (SAS Institute, Inc., Cary, NC, USA). For Experiment 1,
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the percentage of gilts in estrus after P.G. 600 and the onset of boar exposure (Treatment 1) and
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boar exposure alone (Treatments 2 through 5 combined) and the percentages of gilts with normal
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(18 to 24 d; [6]) or abnormal (< 18 d or > 24 d) estrous cycle lengths in each of the five
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treatments were subjected to chi-squares analyses. Treatment to estrus intervals, and age at
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puberty were subjected to ANOVA for a randomized block design using the GLM procedure of
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SAS. The model included treatment as the main effect and pen as the blocking variable. Serum
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progesterone concentrations were analyzed using ANOVA for repeated measures with a model
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that included treatment, gilt within treatment, day and the treatment by day interaction as
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possible sources of variation. Treatment was tested using gilt within treatment as the error term
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and day was tested against treatment by day.
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For Experiment 2, the effect of treatment on the percentage of gilts in estrus by Day 7, Day
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10, or Day 28 was evaluated using chi-squares analyses. Treatment to estrus interval, the length
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of estrus, and farrowing characteristics were evaluated using ANOVA with a model that included
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treatment and pen as possible sources of variation. Gilt body weight at the time of P.G. 600 or
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water treatment was used as a covariate. For both experiments, individual means were compared
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using the PDIFF option of the GLM procedure of SAS.
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3.
Results and Discussion:
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Experiment 1: Effect of P.G. 600 on estrous cycles
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Shown in Table 1 are the effects of P.G. 600 on puberty. Consistent with previous reports
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[2,8], P.G. 600 increased (P < 0.05) the percentage of gilts in estrus within 7 d after treatment
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and for these individuals, decreased (P < 0.01) the interval to first estrus. The response rate to
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P.G. 600 (43.8% in estrus by Day 7 after treatment), however, was less than in previous studies
146
conducted in our laboratory. For example, Garcia et al. [1] treated gilts that were 180 d of age
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with P.G. 600, and within 7 d, 83% (35/42) of the treated animals displayed estrus. Although the
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dichotomy in response rates is not readily explained it could be a consequence of the relatively
149
small number of animals treated in the current study, or a genetic component could be involved.
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In our previous work [1], prolific, maternal-line Yorkshire x Landrace gilts were used, however
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in the current study gilts were farrowed by Yorkshire x Landrace sows mated to terminal Duroc
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boars. Consistent with this hypothesis, Tilton et al. [9] reported that gilts selected to reach
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puberty at a younger age responded more favorably to exogenous treatment with gonadotropins
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than did gilts from a relaxed selection line.
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In the experiment reported here, there was no effect (P = 0.57) of P.G. 600 on the
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percentage of approximately 175 d-old gilts expressing puberty within 28 d after treatment and
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the start of daily boar exposure (table 1), suggesting that P.G. 600 probably did not induce a
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“silent” first estrus followed by standing estrus approximately 21 d later. This is in contrast to
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work by Britt et al. [2] who showed a positive effect of P.G. 600 on the percentage of gilts (165
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to 225 d of age) exhibiting estrus within 28 d after the start of daily estrus detection. Overall,
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there were no differences (P > 0.28) between groups for the percentage of gilts that were
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pubertal by the end of the experiment, age at puberty, or the interval from the start of daily estrus
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detection to first estrus (table 1).
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Effects of P.G. 600 on estrous cycles are summarized in Table 2. The percentage of gilts
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displaying normal estrous cycles was greater (P < 0.05) in gilts not administered P.G. 600 or that
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were administered P.G. 600 at Day 18 of the estrous cycle, compared with gilts administered
167
P.G. 600 at the onset of daily detection of estrus or administered P.G. 600 at Day 12 of the
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estrous cycle, with gilts administered P.G. 600 at Day 6 of the estrous cycle having an
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intermediate value that was not different (P > 0.05) from the other groups. For these normally
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cycling gilts, the length of estrous cycles was greatest (P < 0.05) in gilts administered P.G. 600 at
171
the start of the experiment and least (P < 0.05) for gilts that received no P.G. 600. Although a
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biological explanation for that difference among treatments remains to be determined, it could
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reflect differences in ovulation rate and consequently, circulating progesterone concentrations.
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Gilts selected for high ovulation rates had greater concentrations of progesterone and estrous
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cycle lengths compared to gilts from a random selection line exhibiting low ovulation rates [10].
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Accordingly, increased ovulation rates and circulating concentrations of progesterone in gilts
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treated with P.G. 600 have been reported [7,11]. Although ovulation rates were not determined
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in the current study, gilts treated with P.G. 600 at the start of the experiment and classified as
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exhibiting estrous cycles of normal lengths had the greatest estrous cycle length and as discussed
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below, greater concentrations of progesterone at Day 10 of the estrous cycle compared to gilts
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given P.G. 600 at Day 12 or 18 of the estrous cycle or gilts not receiving gonadotropins.
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The percentage of gilts displaying abnormal estrous cycle lengths was greater (P < 0.05;
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table 1) for gilts receiving P.G. 600 at the initiation of daily boar exposure and detection of estrus
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or at Day 12 of the estrous cycle, compared with gilts receiving P.G. 600 at Day 18 of the estrous
185
cycle or that received no P.G. 600; Gilts administered P.G. 600 at Day 6 of the estrous cycle had
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an intermediate value that was not different (P > 0.05) from the other groups. The length of
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estrous cycles in gilts exhibiting abnormal estrous cycles was variable and not different (P =
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0.75) among groups.
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Progesterone concentrations in serum of gilts was affected by a treatment by day interaction (P = 0.03) as shown in Figure 1.
At the onset of standing estrus (Day 0),
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concentrations of progesterone were minimal and not different among groups (P > 0.05). At Day
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10 of estrous cycles, progesterone concentrations were greater (P < 0.05) for gilts receiving P.G.
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600 at the onset of the study or at Day 6 of the estrous cycle compared with the other three
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groups. At Day 20, serum progesterone concentrations were greatest (P < 0.05) for gilts that
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received P.G. 600 at Day 12 of the cycle and least (P < 0.05) for gilts receiving no P.G. 600.
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Figure 2 shows progesterone concentrations in serum of gilts that received P.G. 600 at Day
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12 of the cycle and that exhibited either normal (n = 9; 20.2 + 0.41 d) or abnormal (n = 5; 32.5 +
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0.41 d) estrous cycle lengths. There was an interaction of cycle type (normal versus abnormal
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length) and day (P = 0.03) on progesterone concentrations in serum.
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600 on Day 12 and that showed an abnormally long inter-estrus interval had greater
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concentrations of progesterone on Day 20 compared to gilts administered P.G. 600 on Day 12 of
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the estrous cycle and that displayed normal estrous cycle lengths. It is well-established that
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accessory CL can be induced in luteal-phase gilts using eCG followed 72 to 96 h later with hCG
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[3, 12], and as a consequence, extend the luteal phase of the estrous cycle. Our findings that
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Gilts administered P.G.
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serum progesterone concentrations remained elevated at Day 20 of the estrous cycle in 33% (5 of
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15) of the gilts administered P.G. 600 on Day 12, and that the inter-estrus interval in these
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animals was approximately 33 d suggests that the gilts ovulated mid-cycle and returned to estrus
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only after regression of the induced CL. These results are consistent with the notion that P.G.
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600, administered in the mid-luteal phase of the estrous cycle may extend the inter-estrus interval
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in gilts.
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producers the need to correctly classify replacement gilts as prepubertal or cycling before
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administering P.G. 600, and illustrate a physiological basis for at least some gilts not responding
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to the compound by displaying estrus within 7 d post-treatment.
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Experiment 2: Use of Matrix and P.G. 600 in combination to synchronize estrus in replacement
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gilts
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From a practical standpoint, the results of this experiment demonstrate to swine
For experiment 2, gilts were assumed to be a mix of cycling and prepubertal individuals,
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although the percentages of each were not ascertained beforehand. As mentioned previously,
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gilts from the genetic base employed here tend to be later-maturing (age at puberty of
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approximately 200 d of age). Moreover, in Experiment 2 boar exposure did not commence until
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after treatment with Matrix and/or P.G. 600.
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Shown in Table 3 are characteristics of estrus for gilts treated with Matrix and/or P.G. 600
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and gilts receiving no exogenous hormones. The percentage of gilts in estrus within 7 d after
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injections was greatest (P < 0.05) and days to estrus least (P < 0.05) for gilts receiving Matrix for
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14 d and P.G. 600 24 h after the last feeding of Matrix. It is not surprising that the percentage of
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gilts in estrus soon after treatment with P.G. 600 alone was low because gilts were purposefully
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treated at an age and weight at which in all likelihood there would have been some gilts already
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cycling. Based on the results of Experiment 1, it is possible that some cycling gilts were treated
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with P.G. 600 mid-cycle, and as a consequence, had an extended luteal phase and a greater inter-
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estrus interval. Consistent with this concept, the days to estrus was greatest (P < 0.05) for gilts
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treated with P.G. 600 alone. The results of this experiment are consistent with previous work from our laboratory
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[7,11,13] and demonstrate that a combination of Matrix, given for 14 or 18 d, and P.G. 600,
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administered 24 h after the last feeding of Matrix, effectively synchronize estrus in gilts. In
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commercial swine operations, it is inevitable that at least occasionally producers will have
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groups of gilts that include both cycling and prepubertal animals, or have groups of replacement
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gilts, the cycling status of which is unknown. We suggest that in those situations, use of a
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combination of Matrix and P.G. 600 is indicated. Indeed, efficacy of this system has been
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demonstrated in commercial settings. On a 100-sow independent operation, 17 gilts were fed
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Matrix for 14 d and treated with P.G. 600 24 h after withdrawal of Matrix; Over 94% of gilts
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were in standing estrus by Day 7 after the last feeding of Matrix [14]. On a 1,000-sow company
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farm, 240 gilts were similarly treated with the combination of Matrix and P.G. 600 and 86.2% of
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gilts were in standing estrus by Day 10 after the last feeding of Matrix (average of 6.4 d from
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Matrix withdrawal to estrus) and conception rate was 85.5% [15]. In that study [15], analysis of
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serum concentrations of progesterone in blood samples collected before treatment indicated that
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26% of the gilts were cycling before Matrix.
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performance between gilts that were cycling and gilts that were prepubertal when feeding of
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Matrix commenced [15].
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There were no differences in reproductive
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In previous studies, gilts that received P.G. 600 after Matrix withdrawal had significantly
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greater ovulation rates than did gilts that received Matrix alone [7,11] and prepubertal gilts
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pretreated with Matrix for 18 d had a numerical, but statistically non-significant increase in
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ovulation rate in response to P.G. 600 compared with prepubertal gilts that received P.G. 600
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only (16.6 vs. 14.4) [7]. The current experiment employed an insufficient number of animals to
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allow firm conclusions regarding effects of Matrix and P.G. 600 in combination on farrowing
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performance, and there were no effects of treatment on total litter size or number born alive
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(table 4). However, total litter size was 12.0, 11.3, 10.1, and 8.9 for gilts receiving Matrix for 14
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d and P.G. 600, Matrix for 7 d and P.G. 600, P.G. 600 only, and no exogenous hormones,
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respectively. Consistent with the numerically greatest litter size, average pig birth weight was
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least for gilts receiving Matrix for 14 d and P.G. 600 (table 4).
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In summary and based on our data, P.G. 600 administered to sexually mature gilts at mid-
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cycle (Day 12) may cause follicular growth, ovulation and formation of induced corpora lutea,
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and may lengthen the inter-estrus interval in approximately 33 percent of animals. Thus, some
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variability in response rates to P.G. 600 among farms may be attributed to producers
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unknowingly treating gilts that are already pubertal and therefore cycling.
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Experiment 2 indicate that Matrix fed for 14 d followed by treatment with P.G. 600 24 h after the
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last feeding of Matrix is an effective system for stimulating and synchronizing estrus in groups
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of gilts that include both cycling and prepubertal animals, or in groups of replacement gilts, the
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cycling status of which is unknown.
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commercial settings using different genetic sources (for example, more prolific, maternal-line
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stock).
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economic viability.
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The results of
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However, this concept needs to be further-tested in
Finally, the system described here must be subjected to an analysis to determine
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Acknowledgements Financial support for this research was provided by the Virginia Pork Industry Board
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(Richmond, VA, USA) and Merck Animal Health (Summit, NJ, USA). The authors thank Terry
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Lee and Lee Johnson for technical assistance.
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References
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[1]
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Garcia A, Estienne MJ, Harper AF, Knight JW. Failure of gonadotropin therapy to induce estrus in gilts treated with a GnRH analog to suppress ovarian activity. Intern J
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Appl Res Vet Med 2004;2:195-200.
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[2]
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Britt JH, Day BN, Webel SK, Brauer MA. Induction of fertile estrus in prepuberal gilts
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by treatment with a combination of pregnant mare’s serum gonadotropin and human
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chorionic gonadotropin. J Anim Sci 1989;67:1148-53. [3]
luteum in swine. Endocrinology 1964;74:355-60.
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Neill JD, Day BN. Relationship of developmental stage to regression of the corpus
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[4]
Estienne MJ, Harper AF.
Type of accommodation during gestation affects growth
performance and reproductive characteristics of gilt offspring. J Anim Sci 2010;88:400-
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DC, 2012.
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NRC. Nutrient Requirements of Swine. 11th Revised ed. Natl Acad Press, Washington
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[6]
Belstra B, Flowers B, See MT, Singleton W. Detection of estrus or heat. Pork
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Information Gateway 2001;Fact Sheet No. 08-01-01. Available at:
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[7]
Estienne MJ, Harper AF, Horsley BR, Estienne CE, Knight JW. Effects of P.G. 600 on
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the onset of estrus and ovulation rate in gilts treated with Regu-mate. J Anim Sci
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2001;79:2757-61. [8]
Knox RV, Tudor KW, Rodriguez-Zas SL, Robb JA.
Effect of subcutaneous vs.
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intramuscular administration of P.G. 600 on estrual and ovulatory responses of
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prepubertal gilts. J Anim Sci 2000;78:1732-37.
Evaluation of response to hormonal therapy in
prepubertal gilts of different genetic lines. J Anim Sci 1995;73:3062-68.
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Tilton SL, Bates RO, Prather RS.
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[10]
Knox RV, Vatzias G, Naber CH, Zimmerman DR. Plasma gonadotropins and ovarian
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hormones during the estrous cycle in high compared to low ovulation rate gilts. J Anim
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Sci 2003;81:249-60.
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[11]
Horsley BR, Estienne MJ, Harper AF, Purcell SH, Baitis HK, Beal WE, Knight JW. Effect of P.G. 600 on the timing of ovulation in gilts treated with altrenogest. J Anim Sci
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2005;83:1690-95.
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[12]
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Rampacek GB, Kraeling RR, Barb CR, Estienne CE, Estienne MJ.
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induced corpora lutea in mature cyclic gilts by human chorionic gonadotropin. J Anim
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Sci 1992;70:3144-48. [13]
Estienne MJ, Harper AF. Case study: Synchronization of estrus and fertility in gilts
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administered P.G. 600® after treatment with Regu-mate® for 14 or 18 days. The Prof
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Anim Sci 2002;18:158-61.
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[14]
Estienne MJ. Use of MATRIX and P.G. 600 in combination to synchronize estrus in
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replacement gilts. Proceedings of the 2011 Meeting of the Southern Section- American
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Society of Animal Science 2011;31.
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[15]
Alberti KA, Pittman JS, Estienne MJ. Comparison of two gilt synchronization protocols
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using MatrixTM and P.G. 600®. Proceedings of the 2011 Meeting of the American
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Association of Swine Veterinarians 2011;289-90.
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Number of gilts 16 64 Puberty by Day 7 of experiment, (%) 7/16 (43.8) 13/64 (20.3) Age at puberty, d 180.5 181.5 Interval from start of experiment to puberty, d 4.7 6.1 Puberty by Day 28 of experiment, (%) 10/16 (62.5) 36/64 (54.7) Age at puberty, d 186.2 189.7 Interval from start of experiment to puberty, d 10.3 14.5 Puberty by end of experiment, (%) 15/16 (93.8) 63/64 (98.4) Age at puberty, d 201.3 203.5 Interval from start of experiment to puberty, d 25.5 28.3 1 Puberty defined as first occurrence of standing estrus in the presence of a mature boar.
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Table 1. Effect of im treatment with 400 IU eCG and 200 IU hCG (P.G. 600; Merck Animal Health, Summit, NJ, USA) on puberty1 in gilts. P.G. 600 at initiation of experiment Item Yes2 No3 SE P
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2
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3
Treatment 1.
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Treatments 2 through 5 combined.
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----0.51 0.31 --2.4 2.4 --4.3 4.3
--0.05 0.19 <0.01 0.57 0.17 0.11 0.28 0.64 0.55
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Table 2. Effect of im treatment with 400 IU eCG and 200 IU hCG (P.G. 600; Merck Animal Health, Summit, NJ, USA) on estrous cycles in gilts P.G. 600 administered at:
333 334
Day 6 16 16
Number of gilts assigned Number of gilts displaying first estrus Normal cycles1, (%) 11/15 (73.3a) 14/16 (87.5a,b) Cycle length, d 21.3a 20.6a,b a Abnormal cycles, (%) 3/15 (20.0 ) 2/16 (12.5a,b) Cycle length, d 37.0 23.7 Estrus then anestrus, (%) 1/15 (6.7) 0/16 (0) 1 Normal cycles defined as 18 to 24 d in length. a,b
Day 12 16 15
Day 18 16 16
9/15 (60.0a) 20.2a,b,c 5/15 (33.3a) 32.5 1/15 (6.7)
16/16 (100b) 19.9b,c 0/16 (0b) --0/16 (0)
Within a row, means with different superscripts differ (P < 0.05).
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No P.G. 600 16 16
SE
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16/16 (100b) 19.7c 0/16 (0b) --0/16 (0)
--0.4 --13.3 ---
0.05 0.01 0.05 0.75 0.23
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Table 3. Characteristics of estrus and estrous cycles in gilts treated with Matrix (Merck Animal Health, Summit, NJ, USA) and/or P.G. 600 (Merck Animal Health) and gilts receiving no exogenous hormones1.
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Matrix 14 d Matrix 7 d P.G. 600 only No Item: + P.G. 600 + P.G. 600 Hormones Number of gilts 12 12 12 12 Percentage of gilts in estrus by Day 7 after P.G. 600 11/12 (91.7a) 6/12 (50.0b) 4/12 (33.3b) 6/12 (50.0b) a b b by Day 10 after P.G. 600 12/12 (100 ) 6/12 (50.0 ) 4/12 (33.3 ) 8/12 (66.6b) a a,b b by Day 28 after P.G. 600 12/12 (100 ) 11/12 (91.7 ) 9/12* (75.0 ) 12/12 (100a) Interval to estrus, d 5.4a 9.2a,b 13.8b 9.1a,b Length of estrus, d 2.03 2.08 1.57 1.90 1 Gilts were checked for estrus daily for 37 d after injection of P.G. 600 and onset of boar exposure.
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*One gilt displayed estrus on Day 31. This gilt is not included in the percentage of gilts displaying estrus.
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a,b
Within a row, means with different superscripts differ (P < 0.05).
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Table 4. Farrowing performance for gilts treated with Matrix (Merck Animal Health, Summit, NJ, USA) and/or P.G. 600 (Merck Animal Health) and gilts receiving no exogenous hormones1. Matrix 14 d Matrix 7 d P.G. 600 only No SE P Item: + P.G. 600 + P.G. 600 Hormones Number of gilts mated 12 11 10 12 ----Gilts farrowing, (%) 7/12 (58.3) 6/11 (54.5) 9/10 (90.0) 11/12 (91.7) --Total Born 12.0 11.3 10.1 8.9 1.9 0.45 Born Live 8.1 11.2 9.0 8.0 1.8 0.53 Pig birth weight, kg 1.41a 1.74a,b 1.93b 1.91b 0.16 0.05 1 With the exception of one gilt in the P.G. 600 only group that was mated on d 31, all gilts were mated within 28 d after P.G. 600 and onset of boar exposure or onset of boar exposure only.
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a,b
Within a row, means with different superscripts differ (P < 0.05).
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Figure Legends
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Figure 1. Progesterone concentrations in gilts treated with 400 IU eCG and 200 IU hCG (P.G.
351
600; Merck Animal Health, Summit, NJ USA) on various days of the estrous cycle. There was
352
an interaction of treatment and day (P = 0.03). Within days, bars with different superscripts
353
differ (P < 0.05).
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Figure 2. Progesterone concentrations in gilts treated with 400 IU eCG and 200 IU hCG (P.G.
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600; Merck Animal Health, Summit, NJ, USA) on Day 12 of the estrous cycle and that exhibited
357
normal (n = 9; 20.2 + 0.41 d) or abnormal (n = 5; 32.5 + 0.41 d) estrous cycle lengths. There
358
was an interaction of cycle type (normal or abnormal length) and day (P = 0.03) on progesterone
359
concentrations. Within days, bars with different superscripts differ (P < 0.05).
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Day relative to onset of estrus
Day of P.G. 600 Start of study Day 6 of cycle Day 12 of cycle Day 18 of cycle None
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Day relative to onset of estrus
Type of Cycle Normal Abnormal