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Effectiveness of a short-term treatment with progesterone injections on synchrony of lambing and fertility in tropical hair sheep
Animal Reproduction Science 126 (2011) 70–75
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Animal Reproduction Science journal homepage: www.elsevier.com/locate/anireprosci
Effectiveness of a short-term treatment with progesterone injections on synchrony of lambing and fertility in tropical hair sheep Marlon Knights a,∗ , Reeza Ramgattie a,1 , Narendra Siew a,1 , Doolarie Singh-Knights a,2 , Gregory Bourne b a b
University of the West Indies, Department of Food Production, St. Augustine, Trinidad and Tobago University of the West Indies, School of Veterinary Medicine, Mount Hope, Trinidad and Tobago
a r t i c l e
i n f o
Article history: Received 10 January 2011 Received in revised form 20 April 2011 Accepted 26 April 2011 Available online 4 May 2011 Keywords: Sheep Estrous synchronization Progeserone
a b s t r a c t The efficacy of using a low cost system for delivering progesterone as part of an estrous synchronization protocol in sheep was evaluated. In experiment 1, Barbados Black Belly ewes (n = 34) and ewe lambs (n = 35; 37.5 ± 0.9 kg) were assigned to be untreated, control animals (C), or to receive PGF2␣ on d0 (PG), or receive two injections of progesterone (200 mg, i.m. each) on D −5 and on D −2.5, prior to PGF2␣ , on D 0 (2PPG). Treatment with 2PPG increased the proportion of animals lambing to the first service (P < 0.05), an effect that was greater in ewe lambs than ewes (treatment × parity; P < 0.05). The interval from ram introduction to lambing and the mean lambing day was less (P = 0.04) in the 2PPG-treated animals compared to control animals. In Experiment 2, lactating ewes from experiment 1 (n = 61) 60–85 days postpartum were assigned within parity and number of lambs reared to remain nursing (S; n = 29) or weaned (W; n = 32) 3 weeks prior to treatment with the 2PPG protocol. There was no effect of treatment on the proportion of animals lambing to the first service or overall, interval from ram introduction to lambing and lambing interval. An 8-month lambing interval was observed in ewes in which estrus was synchronized regardless of physiological state. In conclusion, the two-progesterone injection synchronization protocol may be used as a practical low cost and efficient method of synchronizing estrus to reduce the lambing interval and maximize productivity in tropical breeds of sheep. © 2011 Elsevier B.V. All rights reserved.
1. Introduction The application of estrous synchronization/induction protocols in sheep production systems in the tropics can enhance productivity by increasing the frequency of lamb-
∗ Corresponding author. Current address: Division of Animal and Nutritional Sciences, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. Tel.: +1 304 293 1946; fax: +1 304 293 2232. E-mail address: [email protected] (M. Knights). 1 Current address: BioSciences Agriculture and Food Technologies (BAFT), University of Trinidad and Tobago, Eastern Caribbean Institute of Agriculture and Forestry (ECIAF) Campus, Centeno, Trinidad and Tobago. 2 Current address: Division of Resource Management, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. 0378-4320/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2011.04.019
ing as a result of facilitating the innate ability of tropical sheep to breed and lamb throughout the year. Additionally, estrous synchronization concentrates the lambing periods, allowing for more efficient efforts to be targeted towards reductions in perinatal lamb mortality. Procedures that utilize progesterone or progestogens as part of estrous induction or estrous synchronization protocols have resulted in a greater proportion of anestrous ewes exhibiting fertile estrus (Knights et al., 2001a,b), increased pregnancy rates in peripubertal ewe lambs (Stellflug et al., 2001), a greater synchrony of estrus and lambing, and greater conception and pregnancy rates in estrous cyclic (Dixon et al., 2006) and lactating (Ronquillo et al., 2008) ewes. The initial estrous synchronization protocols utilizing progesterone/progestogens depended on
M. Knights et al. / Animal Reproduction Science 126 (2011) 70–75
long term treatments (>10 days) with implants and intravaginal inserts. This resulted in lesser concentrations of the steroids towards the end of the treatment period and correspondingly lesser conception rates (Vinoles et al., 2001). Other protocols required repeated injections to maintain greater systemic concentrations of progesterone (Gordon, 1958). Treatment with progesterone for a minimum of 5–6 days is necessary for full expression of estrus in response to ram introduction to anestrous ewes (Gordon, 1958). The 5–6-day period of progesterone treatment would also inhibit ovulations ensuring only prostaglandin-responsive corpora lutea are present in ewes that undergoing estrous cycles at regular intervals upon withdrawal of progesterone (Acritopoulou and Haresign, 1980). The application of progesterone using CIDR-g devices for 5 days prior to ram introduction was sufficient to induce fertile estrus in anestrous ewes (Knights et al., 2001a,b). Similarly, the 5day CIDR-g treatment prior to injections of prostaglandins resulted in synchronized estrus and greater conception and pregnancy rates in ewes that initiated estrous cycles before treatment (Dixon et al., 2006). However, the average cost per animal to implement estrous synchronization protocols using both CIDR-g inserts and PGF2␣ is approximately U.S. $7.50. Unfortunately, this cost is prohibitive to the widespread use of such protocols by small ruminant producers in the tropics. A single intramuscular injection of 25 mg progesterone dissolved in olive oil can maintain plasma concentrations above 0.5 ng/mL for 34 h (Contreras-Solis et al., 2008). The short period of progesterone treatment required for estrous induction and synchronization and the relatively long bioavailability of this steroid suggest that using a limited number of injections over a short period, may be a practical, affordable approach to utilize progesterone in estrous induction/synchronization programs. Therefore, the major objective of the present study was to evaluate the efficacy of an estrous synchronization protocol based on short-term treatment with progesterone injections prior to injections with prostaglandin. 2. Materials and methods 2.1. General methodology The animals used in the present study were of at least 7/8 Barbados Blackbelly breeding. They were reared in barns on raised floors at the University of the West Indies Field Station located in Mount Hope, Trinidad and Tobago (10◦ 40 N, 61◦ 31 W). Barbados Blackbelly ewes at this latitude can breed year round (Combellas, 1980). All animals were fed a diet of green forage ad libitum and supplemented with a 18% crude protein concentrate. Rams were reared in a separate building prior to their introduction to the females for breeding for a period of 35 days. 2.2. Experiment 1 The experiment was designed to compare the fertility of ewes and ewe lambs following estrous synchronization using prostaglandin F2␣ alone, or pre-treatment with injec-
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tions of progesterone prior to injections with prostaglandin F2␣ . Barbados Blackbelly animals (n = 69) with a mean body condition score (BCS) of 3.5, (34 non-lactating ewes greater than 150 days postpartum and 35 ewe lambs (37.5 ± 0.9 kg)) were randomly assigned to one of three groups. Group 1 consisted of untreated, control animals (C). The second group of animals (PG) received prostaglandin F2␣ (PGF2␣ , 2 × 10 mg 3 h apart, i.m.; Hawk and Cooper, 1977; Lutalyse® Pharmacia and UpJohn, NY) on Day 0 (D0), while the third group of animals received injections of progesterone (200 mg dissolved in corn oil, i.m., Sigma–Aldrich; 4 ml of a 50 mg/ml solution) on day −5 (D −5) and day −2.5 (D −2.5), followed by PGF2␣ injections on d0 (2PPG). The ewes and ewe lambs were joined with six sexually mature rams on D0 in single sire breeding groups consisting of 10–13 ewes and ewe lambs. The rams were joined with females for a period of 35 days, which allowed between two and three service opportunities. Lambing data for all animals were collected and analyzed. Animals lambing within the first 13 days of the lambing period (Day 147–160) or thereafter (>Day 160) were designated as conceived and lambing to the first and second service periods, respectively. 2.3. Experiment 2 The experiment evaluated the effect of lactational status on fertility in ewes treated with the 2PPG protocol to induce/synchronize estrus. Lactating ewes (n = 61; mean BCS 2.5) 60–85 days postpartum (derived from Experiment 1) were randomly assigned within parity (uniparous or multiparous) and number of lambs reared (rearing type; single or multiple) to remain nursing (S; n = 29) or be weaned (W; n = 32). Three weeks after the lambs were separated from ewes assigned to the weaned treatment group, all animals were treated with the 2PPG synchronization protocol, and rams were introduced on the day of injections with PGF2␣ , (d0) as described in Experiment 1. The six breeding groups were balanced for parity, rearing type and lactation status of ewes. As in Experiment 1, animals lambing within the first 13 days of the lambing period (Day 147–160) or thereafter (>Day 160) were designated as conceived and lambing to the first and second service period, respectively. 2.4. Statistical analysis Data for lambing rate (lambs born per ewe exposed to rams), prolificacy (lambs born per ewe lambing), the interval from ram introduction to lambing and the mean lambing day (day lambed during the lambing period) and lambing interval were analyzed as a completely randomized design with a 2 × 2 or 2 × 2 × 2 factorial arrangement of treatments (Experiment 1 and 2, respectively), using the GLM procedures of SAS (1996). The model included the fixed effects of estrous synchronization treatment, parity (ewes compared to ewe lambs) and the interaction (Experiment 1) and lactational status, rearing type (number of lambs reared single compared to multiple), parity (uniparous compared to multiparous) and the interactions (Experiment 2). When interations were present (P < 0.10)
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means were separated using Tukey’s HSD. Data on the proportion of animals lambing to the first (
reared (Table 2). Overall prolificacy and lambing rate were not affected by either main effects or their interactions. The mean interval from ram introduction to lambing, the mean lambing day and lambing interval was 153 ± 2.8, 8.2 ± 2.8, 249 ± 3.2, respectively, and did not vary with main effects or their interactions.
3.1. Experiment 1
4. Discussion
The mean percentages of animals lambing to the first service period and overall for all treatments were 63% and 97%, respectively (Table 1). Synchronization of estrous using progesterone injections prior to the administration of the prostaglandin increased the proportion of ewe lambs, but not ewes lambing to the first service period (treatment × parity P < 0.05). The 2PPG treatment resulted in more animals lambing to the first service period compared to untreated, control animals (P < 0.05), and animals that were injected with prostaglandin only (P = 0.03; Table 1). Progesterone pre-treatment also tended to increase (P = 0.10) the proportion of animals lambing overall. There was no effect of parity on the percentage of animals lambing to the first service period or overall (Table 1). The mean prolificacy was 2.1 ± 0.9 for animals lambing to the first service and overall. Estrus synchronization treatment did not affect prolificacy to the first service period or overall (Table 1). However, prolificacy of animals conceiving to the first service period tended to be greater in ewes (P = 0.07; 2.4 ± 0.18) compared to ewe lambs (1.9 ± 0.2; Table 1). Lambing rates to the first service period tended to be greater (P = 0.09) in animals in the 2PPG treatment group than animals in the C group, with animals in the PG treatment group showing intermediate lambing rates. Lambing rates also tended to be greater (P = 0.08; Table 1) in ewes compared to ewe lambs. Neither estrous synchronization treatment, parity nor their interaction affected overall lambing rates. The overall mean interval from ram introduction to lambing and the overall mean lambing day (day lambed during the lambing period) was 155 ± 3 and 9.4 ± 2.6, respectively, and was less (P = 0.04) in animals in the 2PPG group compared to control animals. The animals in the PG treatment group had intermediate values. The majority of progesterone-treated ewes (74%) lambed during the first 8 d of the lambing period (Fig. 1). Neither parity, nor the interaction between parity and estrous synchronization treatment affected the interval from ram introduction to lambing or lambing day.
The use of two intramuscular injections of progesterone given 2.5 days apart increased the proportion of animals conceiving to the breeding period immediately after ram introduction. While observations of estrus were not conducted, the greater proportion of progesteronetreated animals lambing within the first 8 days of the lambing period and the shorter period from ram introduction to lambing in progesterone-treated animals indicate that progesterone pre-treatment induced fertile estrus in a greater proportion of animals relative to injections with prostaglandin or in control animals. The mean proportion of animals lambing to the first service period was greater in progesterone pre-treated animals than in those injected with prostaglandin only or those that were untreated. Similar findings were reported by Dixon et al. (2006) when CIDR-g devices were used to provide the progesterone pretreatment. The proportion of progesterone-treated animals lambing to the first service period in the present study (84% and 71% for Experiment 1 and 2, respectively) was somewhat greater than the 56–60% reported by Dixon et al. (2006) indicating a greater conception rate for the synchronized estrus in the present study. Twice as many progesterone-treated ewe lambs conceived at the first service period when compared to untreated lambs or lambs treated with PGF2␣ alone in the present study. Similar findings were reported by Stellflug et al. (2001) for ewe lambs treated with pessaries impregnated with medroxyprogesterone acetate for 12 days and injected with equine chorionic gonadotropin at the time of pessary removal. Apparently, progesterone pre-treatment increases the proportion of animals lambing to the first service by increasing the proportion of animals in heat immediately after treatment, and in some cases increasing the conception rate (Dixon et al., 2006). Additionally, adequate progestogen pre-treatment (concentrations and duration) in ewe lambs might serve to (i) induce puberty in peripubertal anestrous animals as was reported in cattle (Gonzalez-Padilla et al., 1975); (ii) protect the corpus luteum ensuring a fully functional CL is developed (Sheffel et al., 1982; Oldham et al., 1985); and (iii) delay the LH surge to ensure that more viable oocytes are ovulated (Quirke et al., 1981; Sumbung et al., 1987). The results of the present study suggest that the two-injection method provides concentrations of progesterone over the treatment period that is sufficient to induce fertile estrus in a greater proportion of ewes and ewe lambs following injection with PGF2␣ . Estrous synchronization treatment did not affect prolificacy. As such, the greater lambing rates in progesterone pre-treated animals lambing to the first service period were directly related to the greater proportion of these animals lambing to the first service period. The greater
3.2. Experiment 2 The mean percentages of animals lambing to the first service period and overall were 71% and 94%, respectively (Table 2) and were not affected by weaning, number of lambs being reared or parity. The mean prolificacy was 1.4 ± 1.1 and 1.9 ± 1.0 for animals lambing to the first service and overall. Prolificacy and lambing rate of ewes lambing to the first service period was greater (P < 0.05) in multiparous than in uniparous ewes, but was not affected by weaning or number of lambs being
M. Knights et al. / Animal Reproduction Science 126 (2011) 70–75
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Table 1 Fertility of ewes and ewe lambs in control animals (C), or animals in which estrus was synchronized with a single injection of prostaglandin F2␣ (PGF2␣ ) on day 0 (PG), or given two (2) injections of progesterone (200 mg, i.m. each) on day −5 and day −2.5 prior to an injection of PGF2 ␣ (2PPG; Values represent the mean ± standard error). Variables
Treatment C
N Lambing, %a First Serviceb All Services Lambing ratec First Service All Services Prolificacyd First Serviceb All Services Ram Lambe , days Lambing dayf a b c d e f
PG
PPG
Probability
Ewes
Lambs
Ewe
Lambs
Ewe
Lambs
Overall
E vs L
C vs PG
C vs PPG
PG vs PPG
9
13
12
13
13
9
69
55.5 ± 16 100 ± 5.6
41.7 ±± 13 70 ± 15 100 ± 4.7 90.9 ± 5.1
41.7 ± 13 92.3 ± 4.7
84.6 ± 13 100 ± 4.5
88.9 ± 15 100 ± 5.7
63.1 ± 7 97.1 ± 4.1
0.28 0.91
0.62 0.10
0.01 1.00
0.03 0.10
1.6 ± 0.4 2.3 ± 0.3
0.7 ± 0.3 2.0 ± 0.2
1.6 ± 0.4 2.3 ± 0.3
0.8 ± 0.3 1.8 ± 0.2
1.7 ± 0.3 2.1 ± 0.2
1.8 ± 0.4 1.9 ± 0.3
1.32 ± 1.1 2.1 ± 0.9
0.08 0.12
0.77 0.70
0.09 0.48
0.15 0.74
2.8 ± 0.4 2.3 ± 0.3 157 ± 2 11.2 ± 2.3
1.6 ± 0.4 2.1 ± 0.2 157 ± 2 10.8 ± 2.0
2.3 ± 0.3 2.3 ± 0.3 154 ± 2 8.4 ± 2.1
2.0 ± 0.4 1.8 ± 0.2 158 ± 2 12.1 ± 2.0
2.0 ± 0.3 2.1 ± 0.2 154 ± 2 8.1 ± 1.9
2.0 ± 0.3 1.9 ± 0.3 151 ± 2 5.3 ± 2.3
2.1 ± 0.9 2.1 ± 0.9 155 ± 3 9.4 ± 2.6
0.07 0.15 0.91 0.91
0.87 0.59 0.71 0.71
0.54 0.38 0.04 0.04
0.64 0.73 0.09 0.09
Proportion of ewes exposed to rams giving birth. Animals lambing in the first 13 days of the lambing period. Lambs born per ewe exposed to rams. Lambs born per ewe lambing. Period from ram introduction to lambing in days. Day relative to the start of the lambing period.
lambing rates observed in ewes compared to ewe lambs may represent a combination of the numerically greater proportion of ewes lambing to the first service and the tendency for greater prolificacy in ewes compared to ewe lambs. In the second experiment, all animals were pre-treated with progesterone using the 2PPG protocol. Neither the proportion of ewes lambing, prolificacy or lambing rates were affected by the lactation status. Similarly, in another study, no differences in conception rates were observed between lactating and dry ewes pretreated with pro-
gestogen for 8 days prior to injections with equine chorionic gonadotropin (eCG; Warren et al., 1989). In contrast, lesser pregnancy rates were observed in lactating ewes when compared to dry ewes weaned at Day 7 postpartum and treated with progestogen/eCG beginning on Day 30 postpartum (Ronquillo et al., 2008). The fact that conception rates increased in both nonlactating and lactating ewes when the postpartum interval prior to treatment was increased from 30 to 50 days (Warren et al., 1989), suggests that the differences in fertility responses to the progestogen-based estrous syn-
Fig. 1. Cumulative percentages of animals lambing, in control animals (C), or animals in which estrus was synchronized with a single injection of prostaglandin F2␣ (PGF2␣ ) on Day 0 (PG), or given two injections of progesterone (200 mg, i.m. each) on Day −5 and Day −2.5 prior to injection with PGF2 ␣ (2PPG).
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M. Knights et al. / Animal Reproduction Science 126 (2011) 70–75
Table 2 Effects of lactational status (weaned, nursing), rearing type (single, multiple) and parity (uniparous, multiparous) on fertility of ewes following synchronization with a protocol consisting of two injections of progesterone (200 mg, i.m. each) on day −5 and day −2.5 prior to an injection of PGF2 ␣ on D 0 (values represent the mean ± standard error). Lactational status
N Lambing, %a First Serviceb All Services Lambing ratec First Serviceb All Services Prolificacyd First Service All Services Ram-Lambe , days Lambing dayf Lambing Intervalg , days
Rearing type
Parity
Nursing
Weaned
Single
Multiple
Uniparous
Multiparous
22
24
20
26
22
24
59.9 ± 11 89.4 ± 5.5
77.2 ± 9 95.0 ± 4.9
72.7 ± 10 91.7 ± 5.6
64.4 ± 9 92.7 ± 4.8
62.2 ± 10 95.0 ± 5.1
76.3 ± 10 89.4 ± 5.2
1.1 ± 0.3 1.8 ± 0.2
1.6 ± 0.2 2.1 ± 0.2
1.5 ± 0.2 1.9 ± 0.2
1.2 ± 0.2 2.0 ± 0.2
1.0 ± 0.2a 1.7 ± 0.2
1.7 ± 0.2b 2.1 ± 0.2
1.8 ± 0.2 2.1 ± 0.2 153 ± 2 8.2 ± 1.9 248 ± 3
2.0 ± 0.2 2.1 ± 0.2 153 ± 2 7.9 ± 1.6 249 ± 2
2.0 ± 0.2 2.0 ± 0.2 152 ± 2 7.3 ± 2.0 248 ± 3
1.8 ± 0.2 2.1 ± 0.2 154 ± 2 8.8 ± 1.6 249 ± 2
1.6 ± 0.2a 1.8 ± 0.2 154 ± 2 9.4 ± 1.7 250 ± 2
2.2 ± 0.2b 2.3 ± 0.2 152 ± 2 6.7 ± 1.9 247 ± 3
Within a main effect, means in a row without a common letters (a,b) differed (P < 0.05). a Proportion of ewes exposed to rams giving birth. b Animals lambing in the first 13 days of the lambing period. c Lambs born per ewe exposed to rams. d Lambs born per ewe lambing. e Period from ram introduction to lambing in days. f Day relative to the start of the lambing period. g Interval between two successive lambing in days.
chronization protocols in lactating ewes may be related to the duration of the postpartum interval prior to treatment. Prolificacy and lambing rates to the first service were greater in multiparous ewes when compared to uniparous ewes. Growth and sexual maturity occurs long after sheep have attained puberty (Lincoln, 1998), resulting in greater reproductive performance in multiparous ewes compared to ewe lambs (Quirke, 1981) and uniparous ewes (present study). Rearing of multiple lambs resulted in lesser prolificacy, lambing rate to the first service (20%) and an overall lambing rate in uniparous but not in multiparous ewes. However, the interaction between parity and number of lambs reared were not statistically significant. Few studies have examined the effects of parity and the number of reared lambs on fertility. The results of the present study suggest that the reproductive system of uniparous ewes may not be fully mature. Additionally, the reproductive system of uniparous ewes rearing multiple lambs may be severely suppressed by lactation, resulting in reduced responsiveness to progesterone/progestogen-based estrus induction programs postpartum. The interval from ram introduction to lambing and average lamb days and lambing intervals were similar for all treatment combinations. The 8-month lambing interval achieved by ewes in all treatment groups suggests that the two-progesterone injection synchronization protocol can be effectively used to achieve three lamb crops every two years as part of an accelerated lambing program to maximize productivity in tropical breeds of sheep. More importantly, in addition to its technical feasibility, the 2PPG treatment is also a cheaper method of delivering progesterone over short periods. The average cost of the 2PPG treatment is projected to be U.S. $3.70—less than 50% of the cost of the CIDR-g/prostaglandin treatment used by Dixon et al. (2006). Moreover, the actual cost of delivering the
progesterone alone was U.S. $1.20, which is less than 25% of the cost to deliver progesterone using the CIDR-g device. Thus, in conclusion, the two-progesterone injection synchronization protocol may be used as a practical low cost and efficient method of synchronizing estrus in order to reduce the lambing interval and maximize productivity in tropical breeds of sheep. Acknowledgements This research was supported by the Department of Food Production, University of the West Indies St. Augustine Sheep Project. The Authors would like to thank Mr. Errol Fullerton and Darren Wong for their assistance in data collection and general management of the sheep flock. References Acritopoulou, S., Haresign, W., 1980. Response of ewes to a single injection of an analogue of PGF-2 alpha given at different stages of the oestrous cycle. J. Reprod. Fertil. 58, 219–221. de Combellas, J., 1980. Production and reproduction parameters of tropical sheep breeds in improved production systems. Trop. Anim. Prod. 5 (3), 266–272. Contreras-Solis, I., Gomez-Brunet, A., Encinas, T., Gonzalez-Bulnes, A., Santiago-Moreno, J., Lopez-Sebastian, A., 2008. Influence of vehicle on kinetics of exogenous progesterone administered either by subcutaneous and intramuscular routes to sheep. Res. Vet. Sci. 85, 162–165. Dixon, A.B., Knights, M., Pate, J.L., Lewis, P.E., Inskeep, E.K., 2006. Reproductive performance of ewes after 5-day treatment with intravaginal inserts containing progesterone in combination with injection of prostaglandin F2␣ . Reprod. Domest. Anim. 41, 142–148. Gonzalez-Padilla, E., Ruiz, R., LeFever, D., Denham, A., Wiltbank, J.N., 1975. Puberty in beef heifers. III. Induction of fertile estrus. J. Anim. Sci. 40, 1110–1118. Gordon, I., 1958. The use of progesterone and serum gonadotrophin (P.M.S.) in the control of fertility in the sheep II. Studies in the extraseasonal production of lambs. J. Agric. Sci. 50, 152–197. Hawk, H.W., Cooper, B.S., 1977. Sperm transport into the cervix of the ewe after regulation of estrus with prostaglandin or progestogen. J. Anim. Sci. 44, 638–644.
M. Knights et al. / Animal Reproduction Science 126 (2011) 70–75 Knights, M., Hoehn, T., Lewis, P.E., Inskeep, E.K., 2001a. Effectiveness of intravaginal progesterone inserts and FSH for inducing synchronized estrus and increasing lambing rate in anestrous ewes. J. Anim. Sci. 79, 1120–1131. Knights, M., Maze, T.D., Bridges, P.J., Lewis, P.E., Inskeep, E.K., 2001b. Shortterm treatment with a controlled internal drug releasing (CIDR) device and FSH to induce fertile estrus and increase prolificacy in anestrous ewes. Theriogenology 55, 1181–1191. Lincoln, G.A., 1998. Reproductive seasonality and maturation throughout the complete life-cycle in the Mouflon ram (Ovis musimon). Anim. Reprod. Sci. 53, 87–105. Oldham, C.M., Pearce, D.T., Gray, S.J., 1985. Progesterone priming and age of ewe affect the life-span of corpora lutea induced in the seasonally anovulatory Merino ewe by the ‘ram effect’. J. Reprod. Fertil. 75, 29– 33. Quirke, J.F., 1981. Regulation of puberty and reproduction in female lambs: a review. Livest. Proc. Sci. 8, 37–53. Quirke, J.F., Hanrahan, J.P., Gosling, J.P., 1981. Duration of oestrus, ovulation rate, time of ovulation and plasma LH, total oestrogen and progesterone in Galway adult ewes and ewe lambs. J. Reprod. Fertil. 61, 265–272.
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Ronquillo, J.C., Martínez, A.P., Pèrez, C.M.B., Sandoval, B.F., Martin, G.B., Valencia, J., Sánchez, J.G., 2008. Prevention of suckling improves postpartum reproductive responses to hormone treatments in Pelibuey ewes. Anim. Reprod. Sci. 107, 85–93. Sheffel, C.E., Pratt, B.R., Ferrell, W.L., Inskeep, E.K., 1982. Induced corpora lutea in the postpartum beef cow. II. Effects of treatment with progestogen and gonadotropins. J. Anim. Sci. 54, 830–836. Stellflug, J.N., Hatfield, P.G., Wulster-Radcliffe, M.C., Walker, J.W., 2001. Reproductive performance of ewe lambs from ewes from different selection practices with or without induced estrus. Anim. Reprod. Sci. 66, 185–193. Sumbung, F.P., Williamson, P., Carson, R.S., 1987. Response of prepubertal ewes primed with monensin or progesterone to administration of FSH. J. Reprod. Fertil. 81, 317–325. Vinoles, C., Forsberg, M., Banchero, G., Rubianes, E., 2001. Effect of long-term and short-term progestagen treatment on follicular development and pregnancy rate in cyclic ewes. Theriogenology 55, 993–1004. Warren Jr., J.E., Kiesling, D.O., Akinbami, M.A., Price, E.A., Meredith, S., 1989. Conception rates in early postpartum ewes bred naturally or by intrauterine insemination. J. Anim. Sci. 67, 2056–2059.
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Animal Reproduction Science journal homepage: www.elsevier.com/locate/anireprosci
Effectiveness of a short-term treatment with progesterone injections on synchrony of lambing and fertility in tropical hair sheep Marlon Knights a,∗ , Reeza Ramgattie a,1 , Narendra Siew a,1 , Doolarie Singh-Knights a,2 , Gregory Bourne b a b
University of the West Indies, Department of Food Production, St. Augustine, Trinidad and Tobago University of the West Indies, School of Veterinary Medicine, Mount Hope, Trinidad and Tobago
a r t i c l e
i n f o
Article history: Received 10 January 2011 Received in revised form 20 April 2011 Accepted 26 April 2011 Available online 4 May 2011 Keywords: Sheep Estrous synchronization Progeserone
a b s t r a c t The efficacy of using a low cost system for delivering progesterone as part of an estrous synchronization protocol in sheep was evaluated. In experiment 1, Barbados Black Belly ewes (n = 34) and ewe lambs (n = 35; 37.5 ± 0.9 kg) were assigned to be untreated, control animals (C), or to receive PGF2␣ on d0 (PG), or receive two injections of progesterone (200 mg, i.m. each) on D −5 and on D −2.5, prior to PGF2␣ , on D 0 (2PPG). Treatment with 2PPG increased the proportion of animals lambing to the first service (P < 0.05), an effect that was greater in ewe lambs than ewes (treatment × parity; P < 0.05). The interval from ram introduction to lambing and the mean lambing day was less (P = 0.04) in the 2PPG-treated animals compared to control animals. In Experiment 2, lactating ewes from experiment 1 (n = 61) 60–85 days postpartum were assigned within parity and number of lambs reared to remain nursing (S; n = 29) or weaned (W; n = 32) 3 weeks prior to treatment with the 2PPG protocol. There was no effect of treatment on the proportion of animals lambing to the first service or overall, interval from ram introduction to lambing and lambing interval. An 8-month lambing interval was observed in ewes in which estrus was synchronized regardless of physiological state. In conclusion, the two-progesterone injection synchronization protocol may be used as a practical low cost and efficient method of synchronizing estrus to reduce the lambing interval and maximize productivity in tropical breeds of sheep. © 2011 Elsevier B.V. All rights reserved.
1. Introduction The application of estrous synchronization/induction protocols in sheep production systems in the tropics can enhance productivity by increasing the frequency of lamb-
∗ Corresponding author. Current address: Division of Animal and Nutritional Sciences, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. Tel.: +1 304 293 1946; fax: +1 304 293 2232. E-mail address: [email protected] (M. Knights). 1 Current address: BioSciences Agriculture and Food Technologies (BAFT), University of Trinidad and Tobago, Eastern Caribbean Institute of Agriculture and Forestry (ECIAF) Campus, Centeno, Trinidad and Tobago. 2 Current address: Division of Resource Management, West Virginia University, PO Box 6108, Morgantown, WV 26506-6108, United States. 0378-4320/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.anireprosci.2011.04.019
ing as a result of facilitating the innate ability of tropical sheep to breed and lamb throughout the year. Additionally, estrous synchronization concentrates the lambing periods, allowing for more efficient efforts to be targeted towards reductions in perinatal lamb mortality. Procedures that utilize progesterone or progestogens as part of estrous induction or estrous synchronization protocols have resulted in a greater proportion of anestrous ewes exhibiting fertile estrus (Knights et al., 2001a,b), increased pregnancy rates in peripubertal ewe lambs (Stellflug et al., 2001), a greater synchrony of estrus and lambing, and greater conception and pregnancy rates in estrous cyclic (Dixon et al., 2006) and lactating (Ronquillo et al., 2008) ewes. The initial estrous synchronization protocols utilizing progesterone/progestogens depended on
M. Knights et al. / Animal Reproduction Science 126 (2011) 70–75
long term treatments (>10 days) with implants and intravaginal inserts. This resulted in lesser concentrations of the steroids towards the end of the treatment period and correspondingly lesser conception rates (Vinoles et al., 2001). Other protocols required repeated injections to maintain greater systemic concentrations of progesterone (Gordon, 1958). Treatment with progesterone for a minimum of 5–6 days is necessary for full expression of estrus in response to ram introduction to anestrous ewes (Gordon, 1958). The 5–6-day period of progesterone treatment would also inhibit ovulations ensuring only prostaglandin-responsive corpora lutea are present in ewes that undergoing estrous cycles at regular intervals upon withdrawal of progesterone (Acritopoulou and Haresign, 1980). The application of progesterone using CIDR-g devices for 5 days prior to ram introduction was sufficient to induce fertile estrus in anestrous ewes (Knights et al., 2001a,b). Similarly, the 5day CIDR-g treatment prior to injections of prostaglandins resulted in synchronized estrus and greater conception and pregnancy rates in ewes that initiated estrous cycles before treatment (Dixon et al., 2006). However, the average cost per animal to implement estrous synchronization protocols using both CIDR-g inserts and PGF2␣ is approximately U.S. $7.50. Unfortunately, this cost is prohibitive to the widespread use of such protocols by small ruminant producers in the tropics. A single intramuscular injection of 25 mg progesterone dissolved in olive oil can maintain plasma concentrations above 0.5 ng/mL for 34 h (Contreras-Solis et al., 2008). The short period of progesterone treatment required for estrous induction and synchronization and the relatively long bioavailability of this steroid suggest that using a limited number of injections over a short period, may be a practical, affordable approach to utilize progesterone in estrous induction/synchronization programs. Therefore, the major objective of the present study was to evaluate the efficacy of an estrous synchronization protocol based on short-term treatment with progesterone injections prior to injections with prostaglandin. 2. Materials and methods 2.1. General methodology The animals used in the present study were of at least 7/8 Barbados Blackbelly breeding. They were reared in barns on raised floors at the University of the West Indies Field Station located in Mount Hope, Trinidad and Tobago (10◦ 40 N, 61◦ 31 W). Barbados Blackbelly ewes at this latitude can breed year round (Combellas, 1980). All animals were fed a diet of green forage ad libitum and supplemented with a 18% crude protein concentrate. Rams were reared in a separate building prior to their introduction to the females for breeding for a period of 35 days. 2.2. Experiment 1 The experiment was designed to compare the fertility of ewes and ewe lambs following estrous synchronization using prostaglandin F2␣ alone, or pre-treatment with injec-
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tions of progesterone prior to injections with prostaglandin F2␣ . Barbados Blackbelly animals (n = 69) with a mean body condition score (BCS) of 3.5, (34 non-lactating ewes greater than 150 days postpartum and 35 ewe lambs (37.5 ± 0.9 kg)) were randomly assigned to one of three groups. Group 1 consisted of untreated, control animals (C). The second group of animals (PG) received prostaglandin F2␣ (PGF2␣ , 2 × 10 mg 3 h apart, i.m.; Hawk and Cooper, 1977; Lutalyse® Pharmacia and UpJohn, NY) on Day 0 (D0), while the third group of animals received injections of progesterone (200 mg dissolved in corn oil, i.m., Sigma–Aldrich; 4 ml of a 50 mg/ml solution) on day −5 (D −5) and day −2.5 (D −2.5), followed by PGF2␣ injections on d0 (2PPG). The ewes and ewe lambs were joined with six sexually mature rams on D0 in single sire breeding groups consisting of 10–13 ewes and ewe lambs. The rams were joined with females for a period of 35 days, which allowed between two and three service opportunities. Lambing data for all animals were collected and analyzed. Animals lambing within the first 13 days of the lambing period (Day 147–160) or thereafter (>Day 160) were designated as conceived and lambing to the first and second service periods, respectively. 2.3. Experiment 2 The experiment evaluated the effect of lactational status on fertility in ewes treated with the 2PPG protocol to induce/synchronize estrus. Lactating ewes (n = 61; mean BCS 2.5) 60–85 days postpartum (derived from Experiment 1) were randomly assigned within parity (uniparous or multiparous) and number of lambs reared (rearing type; single or multiple) to remain nursing (S; n = 29) or be weaned (W; n = 32). Three weeks after the lambs were separated from ewes assigned to the weaned treatment group, all animals were treated with the 2PPG synchronization protocol, and rams were introduced on the day of injections with PGF2␣ , (d0) as described in Experiment 1. The six breeding groups were balanced for parity, rearing type and lactation status of ewes. As in Experiment 1, animals lambing within the first 13 days of the lambing period (Day 147–160) or thereafter (>Day 160) were designated as conceived and lambing to the first and second service period, respectively. 2.4. Statistical analysis Data for lambing rate (lambs born per ewe exposed to rams), prolificacy (lambs born per ewe lambing), the interval from ram introduction to lambing and the mean lambing day (day lambed during the lambing period) and lambing interval were analyzed as a completely randomized design with a 2 × 2 or 2 × 2 × 2 factorial arrangement of treatments (Experiment 1 and 2, respectively), using the GLM procedures of SAS (1996). The model included the fixed effects of estrous synchronization treatment, parity (ewes compared to ewe lambs) and the interaction (Experiment 1) and lactational status, rearing type (number of lambs reared single compared to multiple), parity (uniparous compared to multiparous) and the interactions (Experiment 2). When interations were present (P < 0.10)
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means were separated using Tukey’s HSD. Data on the proportion of animals lambing to the first (
reared (Table 2). Overall prolificacy and lambing rate were not affected by either main effects or their interactions. The mean interval from ram introduction to lambing, the mean lambing day and lambing interval was 153 ± 2.8, 8.2 ± 2.8, 249 ± 3.2, respectively, and did not vary with main effects or their interactions.
3.1. Experiment 1
4. Discussion
The mean percentages of animals lambing to the first service period and overall for all treatments were 63% and 97%, respectively (Table 1). Synchronization of estrous using progesterone injections prior to the administration of the prostaglandin increased the proportion of ewe lambs, but not ewes lambing to the first service period (treatment × parity P < 0.05). The 2PPG treatment resulted in more animals lambing to the first service period compared to untreated, control animals (P < 0.05), and animals that were injected with prostaglandin only (P = 0.03; Table 1). Progesterone pre-treatment also tended to increase (P = 0.10) the proportion of animals lambing overall. There was no effect of parity on the percentage of animals lambing to the first service period or overall (Table 1). The mean prolificacy was 2.1 ± 0.9 for animals lambing to the first service and overall. Estrus synchronization treatment did not affect prolificacy to the first service period or overall (Table 1). However, prolificacy of animals conceiving to the first service period tended to be greater in ewes (P = 0.07; 2.4 ± 0.18) compared to ewe lambs (1.9 ± 0.2; Table 1). Lambing rates to the first service period tended to be greater (P = 0.09) in animals in the 2PPG treatment group than animals in the C group, with animals in the PG treatment group showing intermediate lambing rates. Lambing rates also tended to be greater (P = 0.08; Table 1) in ewes compared to ewe lambs. Neither estrous synchronization treatment, parity nor their interaction affected overall lambing rates. The overall mean interval from ram introduction to lambing and the overall mean lambing day (day lambed during the lambing period) was 155 ± 3 and 9.4 ± 2.6, respectively, and was less (P = 0.04) in animals in the 2PPG group compared to control animals. The animals in the PG treatment group had intermediate values. The majority of progesterone-treated ewes (74%) lambed during the first 8 d of the lambing period (Fig. 1). Neither parity, nor the interaction between parity and estrous synchronization treatment affected the interval from ram introduction to lambing or lambing day.
The use of two intramuscular injections of progesterone given 2.5 days apart increased the proportion of animals conceiving to the breeding period immediately after ram introduction. While observations of estrus were not conducted, the greater proportion of progesteronetreated animals lambing within the first 8 days of the lambing period and the shorter period from ram introduction to lambing in progesterone-treated animals indicate that progesterone pre-treatment induced fertile estrus in a greater proportion of animals relative to injections with prostaglandin or in control animals. The mean proportion of animals lambing to the first service period was greater in progesterone pre-treated animals than in those injected with prostaglandin only or those that were untreated. Similar findings were reported by Dixon et al. (2006) when CIDR-g devices were used to provide the progesterone pretreatment. The proportion of progesterone-treated animals lambing to the first service period in the present study (84% and 71% for Experiment 1 and 2, respectively) was somewhat greater than the 56–60% reported by Dixon et al. (2006) indicating a greater conception rate for the synchronized estrus in the present study. Twice as many progesterone-treated ewe lambs conceived at the first service period when compared to untreated lambs or lambs treated with PGF2␣ alone in the present study. Similar findings were reported by Stellflug et al. (2001) for ewe lambs treated with pessaries impregnated with medroxyprogesterone acetate for 12 days and injected with equine chorionic gonadotropin at the time of pessary removal. Apparently, progesterone pre-treatment increases the proportion of animals lambing to the first service by increasing the proportion of animals in heat immediately after treatment, and in some cases increasing the conception rate (Dixon et al., 2006). Additionally, adequate progestogen pre-treatment (concentrations and duration) in ewe lambs might serve to (i) induce puberty in peripubertal anestrous animals as was reported in cattle (Gonzalez-Padilla et al., 1975); (ii) protect the corpus luteum ensuring a fully functional CL is developed (Sheffel et al., 1982; Oldham et al., 1985); and (iii) delay the LH surge to ensure that more viable oocytes are ovulated (Quirke et al., 1981; Sumbung et al., 1987). The results of the present study suggest that the two-injection method provides concentrations of progesterone over the treatment period that is sufficient to induce fertile estrus in a greater proportion of ewes and ewe lambs following injection with PGF2␣ . Estrous synchronization treatment did not affect prolificacy. As such, the greater lambing rates in progesterone pre-treated animals lambing to the first service period were directly related to the greater proportion of these animals lambing to the first service period. The greater
3.2. Experiment 2 The mean percentages of animals lambing to the first service period and overall were 71% and 94%, respectively (Table 2) and were not affected by weaning, number of lambs being reared or parity. The mean prolificacy was 1.4 ± 1.1 and 1.9 ± 1.0 for animals lambing to the first service and overall. Prolificacy and lambing rate of ewes lambing to the first service period was greater (P < 0.05) in multiparous than in uniparous ewes, but was not affected by weaning or number of lambs being
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Table 1 Fertility of ewes and ewe lambs in control animals (C), or animals in which estrus was synchronized with a single injection of prostaglandin F2␣ (PGF2␣ ) on day 0 (PG), or given two (2) injections of progesterone (200 mg, i.m. each) on day −5 and day −2.5 prior to an injection of PGF2 ␣ (2PPG; Values represent the mean ± standard error). Variables
Treatment C
N Lambing, %a First Serviceb All Services Lambing ratec First Service All Services Prolificacyd First Serviceb All Services Ram Lambe , days Lambing dayf a b c d e f
PG
PPG
Probability
Ewes
Lambs
Ewe
Lambs
Ewe
Lambs
Overall
E vs L
C vs PG
C vs PPG
PG vs PPG
9
13
12
13
13
9
69
55.5 ± 16 100 ± 5.6
41.7 ±± 13 70 ± 15 100 ± 4.7 90.9 ± 5.1
41.7 ± 13 92.3 ± 4.7
84.6 ± 13 100 ± 4.5
88.9 ± 15 100 ± 5.7
63.1 ± 7 97.1 ± 4.1
0.28 0.91
0.62 0.10
0.01 1.00
0.03 0.10
1.6 ± 0.4 2.3 ± 0.3
0.7 ± 0.3 2.0 ± 0.2
1.6 ± 0.4 2.3 ± 0.3
0.8 ± 0.3 1.8 ± 0.2
1.7 ± 0.3 2.1 ± 0.2
1.8 ± 0.4 1.9 ± 0.3
1.32 ± 1.1 2.1 ± 0.9
0.08 0.12
0.77 0.70
0.09 0.48
0.15 0.74
2.8 ± 0.4 2.3 ± 0.3 157 ± 2 11.2 ± 2.3
1.6 ± 0.4 2.1 ± 0.2 157 ± 2 10.8 ± 2.0
2.3 ± 0.3 2.3 ± 0.3 154 ± 2 8.4 ± 2.1
2.0 ± 0.4 1.8 ± 0.2 158 ± 2 12.1 ± 2.0
2.0 ± 0.3 2.1 ± 0.2 154 ± 2 8.1 ± 1.9
2.0 ± 0.3 1.9 ± 0.3 151 ± 2 5.3 ± 2.3
2.1 ± 0.9 2.1 ± 0.9 155 ± 3 9.4 ± 2.6
0.07 0.15 0.91 0.91
0.87 0.59 0.71 0.71
0.54 0.38 0.04 0.04
0.64 0.73 0.09 0.09
Proportion of ewes exposed to rams giving birth. Animals lambing in the first 13 days of the lambing period. Lambs born per ewe exposed to rams. Lambs born per ewe lambing. Period from ram introduction to lambing in days. Day relative to the start of the lambing period.
lambing rates observed in ewes compared to ewe lambs may represent a combination of the numerically greater proportion of ewes lambing to the first service and the tendency for greater prolificacy in ewes compared to ewe lambs. In the second experiment, all animals were pre-treated with progesterone using the 2PPG protocol. Neither the proportion of ewes lambing, prolificacy or lambing rates were affected by the lactation status. Similarly, in another study, no differences in conception rates were observed between lactating and dry ewes pretreated with pro-
gestogen for 8 days prior to injections with equine chorionic gonadotropin (eCG; Warren et al., 1989). In contrast, lesser pregnancy rates were observed in lactating ewes when compared to dry ewes weaned at Day 7 postpartum and treated with progestogen/eCG beginning on Day 30 postpartum (Ronquillo et al., 2008). The fact that conception rates increased in both nonlactating and lactating ewes when the postpartum interval prior to treatment was increased from 30 to 50 days (Warren et al., 1989), suggests that the differences in fertility responses to the progestogen-based estrous syn-
Fig. 1. Cumulative percentages of animals lambing, in control animals (C), or animals in which estrus was synchronized with a single injection of prostaglandin F2␣ (PGF2␣ ) on Day 0 (PG), or given two injections of progesterone (200 mg, i.m. each) on Day −5 and Day −2.5 prior to injection with PGF2 ␣ (2PPG).
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Table 2 Effects of lactational status (weaned, nursing), rearing type (single, multiple) and parity (uniparous, multiparous) on fertility of ewes following synchronization with a protocol consisting of two injections of progesterone (200 mg, i.m. each) on day −5 and day −2.5 prior to an injection of PGF2 ␣ on D 0 (values represent the mean ± standard error). Lactational status
N Lambing, %a First Serviceb All Services Lambing ratec First Serviceb All Services Prolificacyd First Service All Services Ram-Lambe , days Lambing dayf Lambing Intervalg , days
Rearing type
Parity
Nursing
Weaned
Single
Multiple
Uniparous
Multiparous
22
24
20
26
22
24
59.9 ± 11 89.4 ± 5.5
77.2 ± 9 95.0 ± 4.9
72.7 ± 10 91.7 ± 5.6
64.4 ± 9 92.7 ± 4.8
62.2 ± 10 95.0 ± 5.1
76.3 ± 10 89.4 ± 5.2
1.1 ± 0.3 1.8 ± 0.2
1.6 ± 0.2 2.1 ± 0.2
1.5 ± 0.2 1.9 ± 0.2
1.2 ± 0.2 2.0 ± 0.2
1.0 ± 0.2a 1.7 ± 0.2
1.7 ± 0.2b 2.1 ± 0.2
1.8 ± 0.2 2.1 ± 0.2 153 ± 2 8.2 ± 1.9 248 ± 3
2.0 ± 0.2 2.1 ± 0.2 153 ± 2 7.9 ± 1.6 249 ± 2
2.0 ± 0.2 2.0 ± 0.2 152 ± 2 7.3 ± 2.0 248 ± 3
1.8 ± 0.2 2.1 ± 0.2 154 ± 2 8.8 ± 1.6 249 ± 2
1.6 ± 0.2a 1.8 ± 0.2 154 ± 2 9.4 ± 1.7 250 ± 2
2.2 ± 0.2b 2.3 ± 0.2 152 ± 2 6.7 ± 1.9 247 ± 3
Within a main effect, means in a row without a common letters (a,b) differed (P < 0.05). a Proportion of ewes exposed to rams giving birth. b Animals lambing in the first 13 days of the lambing period. c Lambs born per ewe exposed to rams. d Lambs born per ewe lambing. e Period from ram introduction to lambing in days. f Day relative to the start of the lambing period. g Interval between two successive lambing in days.
chronization protocols in lactating ewes may be related to the duration of the postpartum interval prior to treatment. Prolificacy and lambing rates to the first service were greater in multiparous ewes when compared to uniparous ewes. Growth and sexual maturity occurs long after sheep have attained puberty (Lincoln, 1998), resulting in greater reproductive performance in multiparous ewes compared to ewe lambs (Quirke, 1981) and uniparous ewes (present study). Rearing of multiple lambs resulted in lesser prolificacy, lambing rate to the first service (20%) and an overall lambing rate in uniparous but not in multiparous ewes. However, the interaction between parity and number of lambs reared were not statistically significant. Few studies have examined the effects of parity and the number of reared lambs on fertility. The results of the present study suggest that the reproductive system of uniparous ewes may not be fully mature. Additionally, the reproductive system of uniparous ewes rearing multiple lambs may be severely suppressed by lactation, resulting in reduced responsiveness to progesterone/progestogen-based estrus induction programs postpartum. The interval from ram introduction to lambing and average lamb days and lambing intervals were similar for all treatment combinations. The 8-month lambing interval achieved by ewes in all treatment groups suggests that the two-progesterone injection synchronization protocol can be effectively used to achieve three lamb crops every two years as part of an accelerated lambing program to maximize productivity in tropical breeds of sheep. More importantly, in addition to its technical feasibility, the 2PPG treatment is also a cheaper method of delivering progesterone over short periods. The average cost of the 2PPG treatment is projected to be U.S. $3.70—less than 50% of the cost of the CIDR-g/prostaglandin treatment used by Dixon et al. (2006). Moreover, the actual cost of delivering the
progesterone alone was U.S. $1.20, which is less than 25% of the cost to deliver progesterone using the CIDR-g device. Thus, in conclusion, the two-progesterone injection synchronization protocol may be used as a practical low cost and efficient method of synchronizing estrus in order to reduce the lambing interval and maximize productivity in tropical breeds of sheep. Acknowledgements This research was supported by the Department of Food Production, University of the West Indies St. Augustine Sheep Project. The Authors would like to thank Mr. Errol Fullerton and Darren Wong for their assistance in data collection and general management of the sheep flock. References Acritopoulou, S., Haresign, W., 1980. Response of ewes to a single injection of an analogue of PGF-2 alpha given at different stages of the oestrous cycle. J. Reprod. Fertil. 58, 219–221. de Combellas, J., 1980. Production and reproduction parameters of tropical sheep breeds in improved production systems. Trop. Anim. Prod. 5 (3), 266–272. Contreras-Solis, I., Gomez-Brunet, A., Encinas, T., Gonzalez-Bulnes, A., Santiago-Moreno, J., Lopez-Sebastian, A., 2008. Influence of vehicle on kinetics of exogenous progesterone administered either by subcutaneous and intramuscular routes to sheep. Res. Vet. Sci. 85, 162–165. Dixon, A.B., Knights, M., Pate, J.L., Lewis, P.E., Inskeep, E.K., 2006. Reproductive performance of ewes after 5-day treatment with intravaginal inserts containing progesterone in combination with injection of prostaglandin F2␣ . Reprod. Domest. Anim. 41, 142–148. Gonzalez-Padilla, E., Ruiz, R., LeFever, D., Denham, A., Wiltbank, J.N., 1975. Puberty in beef heifers. III. Induction of fertile estrus. J. Anim. Sci. 40, 1110–1118. Gordon, I., 1958. The use of progesterone and serum gonadotrophin (P.M.S.) in the control of fertility in the sheep II. Studies in the extraseasonal production of lambs. J. Agric. Sci. 50, 152–197. Hawk, H.W., Cooper, B.S., 1977. Sperm transport into the cervix of the ewe after regulation of estrus with prostaglandin or progestogen. J. Anim. Sci. 44, 638–644.
M. Knights et al. / Animal Reproduction Science 126 (2011) 70–75 Knights, M., Hoehn, T., Lewis, P.E., Inskeep, E.K., 2001a. Effectiveness of intravaginal progesterone inserts and FSH for inducing synchronized estrus and increasing lambing rate in anestrous ewes. J. Anim. Sci. 79, 1120–1131. Knights, M., Maze, T.D., Bridges, P.J., Lewis, P.E., Inskeep, E.K., 2001b. Shortterm treatment with a controlled internal drug releasing (CIDR) device and FSH to induce fertile estrus and increase prolificacy in anestrous ewes. Theriogenology 55, 1181–1191. Lincoln, G.A., 1998. Reproductive seasonality and maturation throughout the complete life-cycle in the Mouflon ram (Ovis musimon). Anim. Reprod. Sci. 53, 87–105. Oldham, C.M., Pearce, D.T., Gray, S.J., 1985. Progesterone priming and age of ewe affect the life-span of corpora lutea induced in the seasonally anovulatory Merino ewe by the ‘ram effect’. J. Reprod. Fertil. 75, 29– 33. Quirke, J.F., 1981. Regulation of puberty and reproduction in female lambs: a review. Livest. Proc. Sci. 8, 37–53. Quirke, J.F., Hanrahan, J.P., Gosling, J.P., 1981. Duration of oestrus, ovulation rate, time of ovulation and plasma LH, total oestrogen and progesterone in Galway adult ewes and ewe lambs. J. Reprod. Fertil. 61, 265–272.
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Ronquillo, J.C., Martínez, A.P., Pèrez, C.M.B., Sandoval, B.F., Martin, G.B., Valencia, J., Sánchez, J.G., 2008. Prevention of suckling improves postpartum reproductive responses to hormone treatments in Pelibuey ewes. Anim. Reprod. Sci. 107, 85–93. Sheffel, C.E., Pratt, B.R., Ferrell, W.L., Inskeep, E.K., 1982. Induced corpora lutea in the postpartum beef cow. II. Effects of treatment with progestogen and gonadotropins. J. Anim. Sci. 54, 830–836. Stellflug, J.N., Hatfield, P.G., Wulster-Radcliffe, M.C., Walker, J.W., 2001. Reproductive performance of ewe lambs from ewes from different selection practices with or without induced estrus. Anim. Reprod. Sci. 66, 185–193. Sumbung, F.P., Williamson, P., Carson, R.S., 1987. Response of prepubertal ewes primed with monensin or progesterone to administration of FSH. J. Reprod. Fertil. 81, 317–325. Vinoles, C., Forsberg, M., Banchero, G., Rubianes, E., 2001. Effect of long-term and short-term progestagen treatment on follicular development and pregnancy rate in cyclic ewes. Theriogenology 55, 993–1004. Warren Jr., J.E., Kiesling, D.O., Akinbami, M.A., Price, E.A., Meredith, S., 1989. Conception rates in early postpartum ewes bred naturally or by intrauterine insemination. J. Anim. Sci. 67, 2056–2059.