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Efficacy of the 5-day CO-Synch ovulation synchronization protocol with or without the inclusion of exogenous progesterone in beef cows
The Professional Animal Scientist 32 (2016):82–89; http://dx.doi.org/10.15232/pas.2015-01423 © 2016 American Registry of Professional Animal Scientists. All rights reserved.
E fovulation ficacy of the 5-day CO-Synch synchronization protocol with or without the inclusion of exogenous progesterone in beef cows
P. J. Gunn,*1 PAS, K. C. Culp,†2 R. P. Lemenager,† PAS, and G. A. Bridges‡3 *Department of Animal Science, Iowa State University, Ames 50011; †Department of Animal Sciences, Purdue University, West Lafayette, IN 47907; and ‡North Central Research and Outreach Center, University of Minnesota, Grand Rapids 55744
ABSTRACT Fixed timed-AI (TAI) pregnancy rates were compared in suckled beef cows (n = 883; 5 replications) synchronized using the 5-d CO-Synch protocol with (CDR) or without (NCDR) the inclusion of exogenous progesterone (EAZIBREED CIDR insert; CIDR). Cows were assigned to either the CDR (n = 445) or NCDR (n = 438) treatment by breed, parity, and days postpartum. Blood samples were collected 10 d before and immediately before CIDR insertion (d 0) to determine cyclic status. On d 0 all cows received gonadotropin-releasing hormone (100 μg), and cows in the CDR treatment received a CIDR. On d 5, CIDR were removed in CDR treatment and all cows received 2 separate doses of prostaglandin F2α (25 mg/dose). Cows Corresponding author: [email protected] Current address: The Andersons Inc., Maumee, OH. 3 Current address: Elanco Animal Health, Greenfield, IN. 1 2
were TAI 72 h after CIDR removal (d 8), concurrent with gonadotropin-releasing hormone (100 μg). The proportion of females determined to be cyclic before estrous synchronization was 87.1% (757/869). Timed-AI pregnancy rates were greater (P = 0.05) in CDR (62.3%, n = 438) than NCDR (50.7%, n = 436) treatment. However, a treatment × parity interaction (P = 0.08) was noted relative to TAI. Although CDR obtained greater (P ≤ 0.01) TAI pregnancy rates than NCDR in both primiparous and multiparous groups, difference between treatments was greater in primiparous females (69.0 vs. 46.3% for CDR and NCDR, respectively) than multiparous females (60.7 vs. 51.7% for CDR and NCDR, respectively). To optimize TAI pregnancy rates in beef cows synchronized with the 5-d CO-Synch protocol, inclusion of a CIDR is recommended. Key words: controlled internal drugrelease insert, cyclicity, embryonic loss, gonadotropin-releasing hormone, ovulation
INTRODUCTION The labor and time required to observe estrus as well as cost of estrous and ovulation synchronization implementation schemes have limited the wide-spread adoption of AI in the beef industry (NAHMS, 1997). To reduce the labor required, numerous protocols that synchronize ovulation and facilitate timed AI (TAI) have been developed. One such program is the 5-d CO-Synch + controlled internal drug-release (CIDR) protocol (Bridges et al., 2008). Although the 5-d CO-Synch + CIDR protocol has been demonstrated as an effective protocol to facilitate TAI, the cost associated with the use of CIDR inserts and the additional recommended dose of prostaglandin F2α (PGF2α) at CIDR insert removal (Bridges et al., 2012) may limit its adoption. It has been previously demonstrated that when using the 7-d CO-Synch protocol, inclusion of a progesterone from a CIDR increases TAI pregnancy
87 358 445
Mean ± SD are presented. A 5-d CO-Synch ovulation synchronization protocol with (CDR) or without (NCDR) inclusion of a controlled internal drug-release insert. 3 A total of 5 replications from 3 locations over 2 yr constitute the data set: Feldun Purdue Agricultural Center (FPAC; one replication), Animal Sciences Research and Education Center (ASREC1 and ASREC2 for replications 1 and 2, respectively), and Southern Indiana Purdue Agricultural Center (SIPAC1 and SIPAC2 for replications 1 and 2, respectively). 4 Number of cows. 5 Days postpartum at ovulation synchronization. 6 Circulating blood concentrations of progesterone ≥1 ng/mL before synchronization initiation were categorized at cyclic.
170 170
48 82 130
80 358 438
80.2 ± 2.2 79.8 ± 2.2 69.8 ± 0.8 69.4 ± 0.8 71.7 ± 0.8 71.3 ± 0.8 86.6 (71/82) 91.3 (73/80) 87.3 (309/354) 86.1 (304/353) 87.2 (380/436) 87.1 (377/433)
NCDR CDR
No. Primiparous Multiparous Combined Days postpartum5 Primiparous Multiparous Combined Cyclic,6 % (no./no.) Primiparous Multiparous Combined
2
49 130 179
60 171 231
10 163 173 —
ASREC1 FPAC 4
Item
1
75.1 ± 2.7 — 84.1 ± 4.1 89.1 ± 2.09 73.8 ± 3.3 80.0 ± 1.6 69.0 ± 1.2 68.5 ± 1.1 78.0 ± 1.1 62.9 ± 1.2 69.4 ± 1.4 69.6 ± 0.6 71.2 ± 1.2 68.5 ± 1.1 78.4 ± 1.1 69.3 ± 1.3 70.6 ± 1.3 71.5 ± 0.6 79.2 (38/48) — 100 (10/10) 92.7 (51/55) 91.8 (45/49) 88.9 (143/162) 87.8 (72/82) 84.1 (143/170) 95.7 (156/163) 74.3 (124/167) 94.4 (118/125) 86.7 (613/707) 84.1 (143/170) 96.0 (166/173) 78.8 (175/222) 93.7 (163/174) 87.1 (757/869) 84.6 (110/130)
167 716 883
Combined SIPAC2 ASREC2 SIPAC1
Replication3 Treatment2
Table 1. Characterization of cows in which ovulation was synchronized using the 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone1
5-day CO-Synch with or without exogenous progesterone
83
rates by preventing the premature expression of estrus before PGF2α delivery and TAI (Dejarnette et al., 2001a,b). However, given the 2-dshorter duration between gonadotropin-releasing hormone (GnRH) and PGF2α in the 5- versus the 7-d COSynch protocols, the incidence of premature estrus expression before TAI in the 5-d CO-synch protocol may be less than previously observed with the 7-d CO-Synch protocol. Failing to provide an exogenous progestin source to stimulate the resumption of estrous cycles (Miksch et al., 1978; Smith et al., 1987), however, may result in reduced TAI pregnancy rates in primiparous, thin, or short postpartum cows that are more likely to be anestrus at the initiation of synchronization. Therefore, the objective of this study was to compare TAI pregnancy rates in primiparous and multiparous, as well as cyclic and anestrous, suckled beef cows synchronized with the 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone in the form of a CIDR.
MATERIALS AND METHODS Animals Primiparous (n = 167) and multiparous (n = 716) suckled beef cows managed to be in moderate BCS were used in this study. A total of 5 replications from 3 locations over 2 yr constitute the data set: Feldun Purdue Agricultural Center (FPAC; one replication), Animal Sciences Research and Education Center (ASREC; replications 1 and 2), and Southern Indiana Purdue Agricultural Center (SIPAC; replications 1 and 2). Both FPAC and ASREC were spring-calving herds, whereas SIPAC was a fall-calving herd. Table 1 presents a replication- and treatmentdependent characterization of cattle used in this study.
Treatments All cows were handled in accordance with procedures approved by the Purdue Animal Care and Use
84 Committee. Within replication, cows were stratified by breed, parity, and days postpartum (DPP) and then assigned to treatment. All cows were enrolled in the 5-d CO-Synch protocol (Figure 1) that consisted of administration of 100 μg of GnRH (Cystorelin, Merial, Duluth, GA) on d 0 and 2 doses of PGF2α (Lutalyse, Zoetis Animal Health, Kalamazoo, MI) given between 2 and 10 h apart on d 5. Variation in timing of PGF2α administrations was the result of logistical constraints at some locations. However, it has previously been demonstrated that PGF2α administration at either a 2-, 8-, or 12-h interval is equally effective in the 5-d CO-Synch protocol (Souto et al., 2009). In the present study, treatment consisted of either the inclusion of exogenous progesterone (CIDR insert; CDR; Eazi-Breed CIDR, Zoetis Animal Health; n = 445) or no exogenous progesterone (NCDR; n = 438) during the 5 d between the first GnRH injection and initial PGF2α. On d 8, 72 h after the initial PGF2α injection, all cows were TAI concurrent with GnRH administration (100 μg; Cystorelin, Merial). Cows were handled as commingled groups throughout the experiment and were inseminated at random relative to treatment. Between 7 and 10 d following TAI, fertile bulls were placed with the cows for the remainder of the breeding season (approximately 60 d). Pregnancy diagnosis was performed between 32 and 38 d after TAI using transrectal ultrasonography (variable megahertz linear array transducer, MicroMaxx, Sonosite, Bothell, WA) and used to calculate TAI pregnancy rates. A second pregnancy diagnosis was conducted via transrectal ultrasonography between 32 and 38 d after the conclusion of the breeding season to calculate end-of-season pregnancy rates.
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SIPAC replication 1) and again on d 0 to estimate the proportion of cows that had resumed ovulation-cycle activity at the initiation of the ovulation synchronization protocol. Blood samples were collected via coccygeal venipuncture in 6-mL tubes containing EDTA (BD Vacutainer; Becton Dickinson, Franklin Lakes, NJ) and immediately placed on ice. Samples were centrifuged within 8 h after collection at 1,750 × g for 25 min at 4°C; plasma was recovered, transferred to 5-mL polystyrene tubes, and frozen at −20°C until it was analyzed for progesterone concentration. Progesterone concentration was determined using a commercially available RIA kit (CoatA-Count, Siemens Medical Solutions Diagnostics, Los Angeles, CA). For 4 assays, the average intraassay CV was 2.1% and the interassay CV for pooled plasma samples containing 0.19 and 6.35 ng/mL of progesterone were 6.4 and 7.2%, respectively. The average sensitivity was 0.04 ng/mL (95% CI). For assessment of reproductive status, cows that had progesterone concentrations ≥1 ng/mL in either or both plasma samples were considered to have resumed regular estrous-cycle activity.
Data and Statistical Analysis Timed-AI pregnancy rate was defined as the proportion of all treated cows that were determined to be pregnant as a result of TAI. Breedingseason pregnancy rate was the proportion of all treated cows that became pregnant to TAI or bull exposure.
Cows diagnosed as pregnant to timedAI at initial pregnancy detection that were subsequently diagnosed as not pregnant to TAI at final pregnancy detection were classified as having embryonic loss. Embryonic-loss rate was calculated as the number of cows that aborted divided by the number of cows diagnosed as pregnant to TAI at initial pregnancy detection. For statistical analysis, cows were classified as either primiparous (2 yr of age) or multiparous (≥3 yr of age). The GLIMMIX procedure of SAS was used to analyze all categorical data. There were no significant treatment × year or treatment × locations interactions (P > 0.10) for any of the variables measured; therefore, data within each location and year were analyzed as an individual replication, for a total of 5 replications. For dependent variables of interest, the initial model included the fixed main effects of treatment, parity, season, and reproductive status as well as all appropriate interactions, and replication was included as a random effect. Interactions with a significance value of P > 0.15 were removed from the model in a stepwise manner to derive the final reduced model for each variable. As the effects of AI technician and AI sire were confounded within replication, the effect of AI sire, AI technician, treatment, and the appropriate interactions were evaluated first within replication. Although technician and AI sire were significant within some replications, there were no AI sire or AI technician × treatment interactions (P > 0.15); thus,
Reproductive Status Blood samples were collected on either d −11 (ASREC replication 2 and SIPAC replication 2) or d −7 (FPAC, ASREC replication 1, and
Figure 1. Experimental protocol used to synchronize ovulation in suckled beef cows. Cows were administered the 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone (controlled internal drug-release insert; CIDR). GnRH = gonadotropin-releasing hormone; PGF2α = prostaglandin F2α.
85
5-day CO-Synch with or without exogenous progesterone
these variables were subsequently removed. In an ancillary analysis, cows were classified into 6 groups based on number of DPP at d 0 (<41, 41–50, 51–60, 61–70, 71–80, and >80) to analyze the effect of DPP on cyclicity as well as pregnancy and embryonicloss parameters previously described. The initial model included the main effects of treatment and DPP grouping as well as the appropriate interac-
tion, with replication included as a random effect. The treatment × DPP grouping interaction was removed if not significant (P > 0.15). Differences were considered to be significant when P ≤ 0.05 and a tendency when 0.05 < P ≤ 0.10.
RESULTS AND DISCUSSION The objective of this study was to determine whether TAI pregnancy
rates differed in beef cows synchronized with the 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone. As the use of a CIDR represents the greatest pharmaceutical cost of this ovulation synchronization protocol, the ability to remove this product while maintaining similar TAI pregnancy may increase the adoption of ovulation synchronization and AI in the beef industry. Results of the present
Table 2. Timed AI, overall breeding-season pregnancy rates, and embryonic-loss rates in beef cows synchronized for ovulation with a 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone Treatment1 CDR, % (no./no.)2
Item Timed-AI pregnancy rate Treatment Parity4 Primiparous Multiparous Reproductive status5 Cyclic Anestrous Breeding-season pregnancy rate Treatment Parity Primiparous Multiparous Reproductive status Cyclic Anestrous Embryonic-loss rate6 Treatment Parity Primiparous Multiparous Reproductive status Cyclic Anestrous
62.3 (276/443)a 69.0 (60/87)a 60.7 (216/356)a 63.5 (241/380)a 55.4 (31/56) 90.5 (402/444) 83.9 (73/87) 92.2 (329/357) 91.0 (345/379) 85.7 (48/56) 2.5 (7/276) 3.3 (2/60) 2.3 (5/216) 2.9 (7/241) 0 (0/31)
NCDR, % (no./no.)2
50.7 (221/436)b 46.3 (37/80)b 51.7 (184/356)b 49.7 (187/377)b 57.4 (32/56) 89.9 (393/437) 83.8 (67/80) 91.3 (326/357) 90.5 (341/377) 89.1 (49/55) 3.2 (7/221) 2.7 (1/37) 3.3 (6/184) 3.2 (6/187) 3.2 (1/31)
Combined, % (no./no.)2
56.5 (497/879) 58.1 (97/157) 56.2 (400/712) 56.5 (428/757) 56.3 (63/112) 90.2 (795/881) 83.8 (140/167)y 91.7 (655/714)z 90.7 (686/756) 87.4 (97/111) 2.8 (14/497) 3.1 (3/97) 2.8 (11/400) 3.0 (13/428) 1.6 (1/62)
P-value3
0.05 0.35 0.76 0.94 0.004 0.14 0.68 0.79 0.52
Within a row, means lacking a common superscript differ due to treatment (P ≤ 0.05). Within a column, means lacking a common superscript differ (P ≤ 0.05). 1 A 5-d CO-Synch ovulation synchronization protocol with (CDR) or without (NCDR) inclusion of a controlled internal drug-release insert. 2 Results are presented as the proportion of cows pregnant within treatment and classification. The number of cows pregnant divided by the number of cows in which pregnancy status was determined is presented in parentheses. 3 Main effects of treatment, parity, and reproductive status. 4 A treatment × parity interaction was observed (P = 0.08; Figure 2). 5 A treatment × reproductive status interaction was observed (P = 0.14; Figure 3). 6 Of cows diagnosed as pregnant to timed AI at initial pregnancy detection, the proportion of cows that were diagnosed as open or not pregnant to timed AI at final pregnancy detection. a,b y,z
86 study demonstrate that removal of exogenous progesterone in the 5-d approach reduced TAI pregnancy rates and thus is not recommended. Reproductive status was analyzed in 869 of the 883 cows enrolled in the study, with 87.1% of cows determined to be cyclic at treatment initiation (Table 1). Across replications, the proportion of cyclic cows ranged from 78.8 to 96.0%. Reproductive status was not different between treatments (P = 0.98; 87.2 vs. 87.1% for CDR and NCDR, respectively) and was not affected by parity (P = 0.62; 88.9 and 86.7% for primiparous and multiparous, respectively). It has been reported that the average postpartum interval to first estrus is less than 60 d in adequately nourished cows (Bailey et al., 1988; Houghton et al., 1990). Because 77.3% of cows in the current study were greater than 60 DPP at the initiation of ovulation synchronization, the large proportion of cyclic cows was not surprising. We acknowledge that the low proportion of anestrous females in this study is a limitation of the data set, as one potential benefit of progesterone inclusion in an estrous synchronization protocol is stimulating estrous cycles in anestrous females (Fike et al., 1997; Perry et al., 2004). The proportion of cyclic cows at treatment initiation was unexpectedly not affected by parity. Although these results are supported by Lamb et al. (2001), previous studies have demonstrated that primiparous cows are more likely to be anestrous at the initiation of the breeding season when compared with multiparous females (Short and Adams, 1988; Short et al., 1990; Stevenson et al., 2003a; Larson et al., 2006). The lack of difference in cyclicity relative to parity in the current study is likely a result of primiparous females averaging 80 DPP at treatment initiation, which was 10 d more than multiparous females. Timed-AI pregnancy rate, breedingseason pregnancy rate, and embryonic-loss rate in relation to treatment, parity, and reproductive status are located in Table 2. Timed-AI pregnancy rates were greater in CDR-
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Figure 2. Effect of the 5-d CO-Synch ovulation synchronization protocol with (CDR) or without (NCDR) exogenous progesterone (controlled internal drug-release insert) on timed-AI pregnancy rates of suckled beef cows at each location (overall P-value = 0.05): Feldun Purdue Agricultural Center (FPAC; one replication), Animal Sciences Research and Education Center (ASREC1 and ASREC2 for replications 1 and 2, respectively), and Southern Indiana Purdue Agricultural Center (SIPAC1 and SIPAC2 for replications 1 and 2, respectively).
than NCDR-treated cows (P < 0.001; Table 2 and Figure 2). It has been previously demonstrated that failing to include a CIDR insert in the 7-d CO-Synch protocol reduces pregnancy success in beef cows (Lamb et al., 2001; Stevenson et al., 2003b; Larson et al., 2006), which is likely due in part to expression of premature estrus in CO-Synch protocols. To this point, Dejarnette et al. (2001a,b) reported that in the 7-d protocol, failure to include a CIDR resulted in 8 to 10%
of cows displaying premature estrus. Premature estrus expression likely occurs more frequently in cows that fail to respond to GnRH. Yet, it has been hypothesized that 2 fewer days between GnRH and PGF2α in the 5-d CO-Synch protocol when compared with the 7-d CO-Synch protocol may reduce the occurrence of premature estrus. However, estrous expression was not recorded in this study. The main effects of parity and reproductive status did not affect preg-
Figure 3. Treatment × parity interaction (P = 0.08) for timed-AI pregnancy rates in beef cows that had ovulation synchronized using the 5-d CO-Synch protocol with (CDR) or without (NCDR) exogenous progesterone (controlled internal drug-release insert). Across parity, bars lacking a common letter differ (P ≤ 0.05).
87
Within a row, means lacking a common superscript differ due to treatment (P ≤ 0.05). Within a row, means lacking a common superscript tend to differ (0.05 < P ≤ 0.10). 1 There were no interactions (P > 0.15) between days postpartum classification and treatment relative to reproductive response variables. 2 Days postpartum at initiation of ovulation synchronization. 3 Results are presented as the proportion of cows within treatment and classification. The number of cows with a positive response for the variable of interest divided by the number of cows in which status was determined is presented in parentheses. 4 Of cows diagnosed as pregnant to timed AI at initial pregnancy detection, the proportion of cows that were diagnosed as open or not pregnant to timed AI at final pregnancy detection. y,z
92.6 (249/269) 58.8 (160/272) 91.2 (250/274) 2.5y (4/160) 90.5 (134/148) 50.3 (74/147) 87.1 (128/147) 8.1z (6/74) 68.6 (57/83) 55.9 (47/84) 86.9 (73/89) 2.1y (1/47) 66.7 (42/63) 52.3 (33/63) 90.4 (57/63) 3.0y (1/33) 54.9 (28/51) 56.8 (29/51) 88.2 (45/81) 0y (0/29) Cyclicity Timed-AI pregnancy rate Breeding-season pregnancy rate Embryonic-loss rate4
a–c
<0.001 0.57 0.46 0.09 96.9 (247/255) 58.8 (154/262) 92.4 (242/262) 1.3y (2/154)
P-value >80
c
71–80
b b
61–70 51–60
a a
a
41–50 <41 Item
Days postpartum,2 % (no./no.)3
nancy to TAI (P ≥ 0.37). Although the number of anestrous and primiparous females was limited in this study, these results are still surprising given the ability of a CIDR to induce cyclic status and the propensity for primiparous females to be anestrous at the initiation of the breeding season. However, we acknowledge that GnRH alone can also induce cyclicity in anestrous females. Even though it has been reported that response to GnRH is improved when progesterone concentrations are suppressed (Perry and Perry, 2009), response to GnRH in anestrous females is variable, reported from 16.5% (Stevenson et al., 2000) to 88.9% (Geary et al., 2000). Thus, exposing cows to progesterone via CIDR in combination with GnRH is more consistently effective in stimulating cyclicity than GnRH alone (Stevenson et al., 2003a). In addition to the 7-d CO-Synch protocol being less effective in stimulating estrous-cycle activity in anestrous females when compared with the 7-d CO-Synch + CIDR protocol (Stevenson et al., 2003a), reduced pregnancy rates in the 7-d CO-Synch protocol is in part due to premature expression of estrus of cyclic females before TAI (Stevenson et al., 2000; Dejarnette et al., 2001a,b). As previously stated, it was hypothesized that the 2-d difference in duration of the 5- and 7-d protocols may reduce the number of cows displaying premature estrous before TAI. Although this variable was not directly assessed, results from this study demonstrate that as in the 7-d CO-Synch protocol, exogenous progesterone administration improves pregnancy rates to TAI in the 5-d CO-Synch protocol. There was a tendency for a treatment × parity interaction (P = 0.08) for TAI pregnancy rates (Figure 3). Although CDR obtained greater (P ≤ 0.01) TAI pregnancy rates than NCDR in both primiparous and multiparous groups, difference between treatments was greater in primiparous females (69.0 vs. 46.3% for CDR and NCDR, respectively) than multiparous females (60.7 vs. 51.7% for CDR and NCDR, respectively). Because
Table 3. Effect of days postpartum on reproductive parameters of beef cows synchronized for ovulation with a 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone1
5-day CO-Synch with or without exogenous progesterone
88 cyclicity was similar between primiparous and multiparous cows, this interaction is not easily explained; however, the number of primiparous and anestrous females enrolled in this study are acknowledged as a limitation of the data set. Timed-AI pregnancy rate was not affected by DPP category (P = 0.57; Table 3). However, a seasonal effect on TAI pregnancy success was observed (P < 0.001; Figure 2) independent of treatment, parity, and reproductive status; spring-calving cows (ASREC and FPAC) had greater TAI pregnancy rates than fall-calving cows (SIPAC; 65.7 vs. 46.4%, respectively). This seasonal or location effect on TAI pregnancy rates was somewhat surprising because fall-calving cows had the longer postpartum interval and a larger proportion of cyclic females at treatment initiation. This is likely because of differences in production systems; fall-calving cows were sustained on stockpiled endophyteinfected fescue before the breeding season, whereas the other 3 springcalving herds had greater access to legumes and cool-season grasses. Previous studies have demonstrated that grazing endophyte-infected fescue may exhibit suppressed first-service AI conception rates in heifers (Washburn et al., 1989) and calving rates in cows (Gay et al., 1988; Washburn and Green, 1991). Reduced fertility in endophyte-fed females may be a result of reduced implantation rates, as Varney et al. (1987) reported in female rats fed an endophyte seed diet. Although CDR improved pregnancy to TAI when compared with NCDR, overall breeding-season pregnancy did not differ as a result of estrous synchronization treatment (P = 0.94; Table 2). Late embryonic loss in this study was 2.8%, and although not different due to treatment (P = 0.68), embryonic loss was similar to that reported by Stevenson et al. (2015). Similar to the current study, Galvão et al. (2004) reported no differences of embryonic loss between d 27 and 41 after AI when comparing dairy cows synchronized with either the 7-d
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CO-Synch or 7-d CO-Synch + CIDR protocol.
IMPLICATIONS Inclusion of exogenous progesterone improved pregnancy rates in cows synchronized for ovulation with the 5-d CO-Synch protocol. Moreover, the increase of 11.6 percentage units in TAI pregnancy rates for cows treated with exogenous progesterone likely more than offsets the cost of progesterone inserts for the entire herd. Thus, to optimize TAI pregnancy rates in beef cows synchronized with the 5-d CO-Synch protocol, use of exogenous progesterone is recommended.
ACKNOWLEDGMENTS The authors extend their appreciation to Zoetis Animal Health for donation of CIDR inserts and prostaglandin F2α (Lutalyse), as well as to B. Defreese, J. Holmes, L. Houghton, J. Tower, and R. Huntrods for providing assistance with data collection.
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5-day CO-Synch with or without exogenous progesterone ing device insertion on the gonadotropin-releasing hormone-induced luteinizing hormone surge and ovulatory response. J. Anim. Sci. 87:3983–3990.
2009. Use of a single dose of cloprostenol sodium in the 5-d CO-Synch + CIDR synchronization program in postpartum beef cows. J. Anim. Sci. 87(Suppl. 1):465. (Abstr.).
Perry, G. A., M. F. Smith, and T. W. Geary. 2004. Ability of intravaginal progesterone inserts and melengestrol acetate to induce estrous cycles in postpartum beef cows. J. Anim. Sci. 82:695–704.
Stevenson, J. S., S. L. Hill, G. A. Bridges, J. E. Larson, and G. C. Lamb. 2015. Progesterone status, parity, body condition, and days postpartum before estrus or ovulation synchronization in suckled beef cattle influence artificial insemination pregnancy outcomes. J. Anim. Sci. 93:2111–2123. http://dx.doi. org/10.2527/jas.2014-8391.
Short, R. E., and D. C. Adams. 1988. Nutritional and hormonal interrelationships in beef cattle reproduction. Can. J. Anim. Sci. 68:29–39. Short, R. E., R. A. Bellows, R. B. Staigmiller, J. G. Berardinelli, and E. E. Custer. 1990. Physiological mechanisms controlling anestrus and infertility in postpartum beef cattle. J. Anim. Sci. 68:799–816. Smith, V. G., J. R. Chenault, J. F. McAllister, and J. W. Lauderdale. 1987. Response of postpartum beef cows to exogenous progestogens and gonadotropin releasing hormone. J. Anim. Sci. 64:540–551. Souto, L. A., M. Maquivar, M. L. Mussard, G. A. Bridges, D. G. Grum, and M. L. Day.
Stevenson, J. S., S. K. Johnson, M. A. Medina-Britos, A. M. Richardson-Adams, and G. C. Lamb. 2003b. Resynchronization of estrus in cattle of unknown pregnancy status using estrogen, progesterone, or both. J. Anim. Sci. 81:1681–1692. Stevenson, J. S., S. K. Johnson, and G. A. Milliken. 2003a. Symposium Paper: Incidence of postpartum anestrus in suckled beef cattle: Treatments to induce estrus, ovulation, and conception. Prof. Anim. Sci. 19:124–134. Stevenson, J. S., K. E. Thompson, W. L. Forbes, G. C. Lamb, D. M. Grieger, and L.
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R. Corah. 2000. Synchronizing estrus and (or) ovulation in beef cows after combinations of GnRH, norgestomet, and prostaglandin F2α with or without timed insemination. J. Anim. Sci. 78:1747–1758. Varney, D. R., M. Nderfu, S. L. Jones, R. Newsome, M. R. Siegel, and P. M. Zavos. 1987. The effects of feeding endophyte infected tall fescue seed on reproductive performance in female rats. Comp. Biochem. Physiol. C 87:171–175. Washburn, S. P., and J. T. Green Jr. 1991. Performance of replacement beef heifers on endophyte-infected fescue pastures. Pages 1–4 in Proc. 40th Annu. Conf. North Carolina Cattlemen’s Assoc. North Carolina State Univ., Raleigh. Washburn, S. P., J. T. Green Jr., and B. H. Johnson. 1989. Effects of endophyte presence in tall fescue on growth, puberty, and conception in Angus heifers. Page 80 in Proc. Tall Fescue Toxicosis Workshop. South. Reg. Info. Exch. Group 37 (SRIEG-37), Atlanta, GA.
E fovulation ficacy of the 5-day CO-Synch synchronization protocol with or without the inclusion of exogenous progesterone in beef cows
P. J. Gunn,*1 PAS, K. C. Culp,†2 R. P. Lemenager,† PAS, and G. A. Bridges‡3 *Department of Animal Science, Iowa State University, Ames 50011; †Department of Animal Sciences, Purdue University, West Lafayette, IN 47907; and ‡North Central Research and Outreach Center, University of Minnesota, Grand Rapids 55744
ABSTRACT Fixed timed-AI (TAI) pregnancy rates were compared in suckled beef cows (n = 883; 5 replications) synchronized using the 5-d CO-Synch protocol with (CDR) or without (NCDR) the inclusion of exogenous progesterone (EAZIBREED CIDR insert; CIDR). Cows were assigned to either the CDR (n = 445) or NCDR (n = 438) treatment by breed, parity, and days postpartum. Blood samples were collected 10 d before and immediately before CIDR insertion (d 0) to determine cyclic status. On d 0 all cows received gonadotropin-releasing hormone (100 μg), and cows in the CDR treatment received a CIDR. On d 5, CIDR were removed in CDR treatment and all cows received 2 separate doses of prostaglandin F2α (25 mg/dose). Cows Corresponding author: [email protected] Current address: The Andersons Inc., Maumee, OH. 3 Current address: Elanco Animal Health, Greenfield, IN. 1 2
were TAI 72 h after CIDR removal (d 8), concurrent with gonadotropin-releasing hormone (100 μg). The proportion of females determined to be cyclic before estrous synchronization was 87.1% (757/869). Timed-AI pregnancy rates were greater (P = 0.05) in CDR (62.3%, n = 438) than NCDR (50.7%, n = 436) treatment. However, a treatment × parity interaction (P = 0.08) was noted relative to TAI. Although CDR obtained greater (P ≤ 0.01) TAI pregnancy rates than NCDR in both primiparous and multiparous groups, difference between treatments was greater in primiparous females (69.0 vs. 46.3% for CDR and NCDR, respectively) than multiparous females (60.7 vs. 51.7% for CDR and NCDR, respectively). To optimize TAI pregnancy rates in beef cows synchronized with the 5-d CO-Synch protocol, inclusion of a CIDR is recommended. Key words: controlled internal drugrelease insert, cyclicity, embryonic loss, gonadotropin-releasing hormone, ovulation
INTRODUCTION The labor and time required to observe estrus as well as cost of estrous and ovulation synchronization implementation schemes have limited the wide-spread adoption of AI in the beef industry (NAHMS, 1997). To reduce the labor required, numerous protocols that synchronize ovulation and facilitate timed AI (TAI) have been developed. One such program is the 5-d CO-Synch + controlled internal drug-release (CIDR) protocol (Bridges et al., 2008). Although the 5-d CO-Synch + CIDR protocol has been demonstrated as an effective protocol to facilitate TAI, the cost associated with the use of CIDR inserts and the additional recommended dose of prostaglandin F2α (PGF2α) at CIDR insert removal (Bridges et al., 2012) may limit its adoption. It has been previously demonstrated that when using the 7-d CO-Synch protocol, inclusion of a progesterone from a CIDR increases TAI pregnancy
87 358 445
Mean ± SD are presented. A 5-d CO-Synch ovulation synchronization protocol with (CDR) or without (NCDR) inclusion of a controlled internal drug-release insert. 3 A total of 5 replications from 3 locations over 2 yr constitute the data set: Feldun Purdue Agricultural Center (FPAC; one replication), Animal Sciences Research and Education Center (ASREC1 and ASREC2 for replications 1 and 2, respectively), and Southern Indiana Purdue Agricultural Center (SIPAC1 and SIPAC2 for replications 1 and 2, respectively). 4 Number of cows. 5 Days postpartum at ovulation synchronization. 6 Circulating blood concentrations of progesterone ≥1 ng/mL before synchronization initiation were categorized at cyclic.
170 170
48 82 130
80 358 438
80.2 ± 2.2 79.8 ± 2.2 69.8 ± 0.8 69.4 ± 0.8 71.7 ± 0.8 71.3 ± 0.8 86.6 (71/82) 91.3 (73/80) 87.3 (309/354) 86.1 (304/353) 87.2 (380/436) 87.1 (377/433)
NCDR CDR
No. Primiparous Multiparous Combined Days postpartum5 Primiparous Multiparous Combined Cyclic,6 % (no./no.) Primiparous Multiparous Combined
2
49 130 179
60 171 231
10 163 173 —
ASREC1 FPAC 4
Item
1
75.1 ± 2.7 — 84.1 ± 4.1 89.1 ± 2.09 73.8 ± 3.3 80.0 ± 1.6 69.0 ± 1.2 68.5 ± 1.1 78.0 ± 1.1 62.9 ± 1.2 69.4 ± 1.4 69.6 ± 0.6 71.2 ± 1.2 68.5 ± 1.1 78.4 ± 1.1 69.3 ± 1.3 70.6 ± 1.3 71.5 ± 0.6 79.2 (38/48) — 100 (10/10) 92.7 (51/55) 91.8 (45/49) 88.9 (143/162) 87.8 (72/82) 84.1 (143/170) 95.7 (156/163) 74.3 (124/167) 94.4 (118/125) 86.7 (613/707) 84.1 (143/170) 96.0 (166/173) 78.8 (175/222) 93.7 (163/174) 87.1 (757/869) 84.6 (110/130)
167 716 883
Combined SIPAC2 ASREC2 SIPAC1
Replication3 Treatment2
Table 1. Characterization of cows in which ovulation was synchronized using the 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone1
5-day CO-Synch with or without exogenous progesterone
83
rates by preventing the premature expression of estrus before PGF2α delivery and TAI (Dejarnette et al., 2001a,b). However, given the 2-dshorter duration between gonadotropin-releasing hormone (GnRH) and PGF2α in the 5- versus the 7-d COSynch protocols, the incidence of premature estrus expression before TAI in the 5-d CO-synch protocol may be less than previously observed with the 7-d CO-Synch protocol. Failing to provide an exogenous progestin source to stimulate the resumption of estrous cycles (Miksch et al., 1978; Smith et al., 1987), however, may result in reduced TAI pregnancy rates in primiparous, thin, or short postpartum cows that are more likely to be anestrus at the initiation of synchronization. Therefore, the objective of this study was to compare TAI pregnancy rates in primiparous and multiparous, as well as cyclic and anestrous, suckled beef cows synchronized with the 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone in the form of a CIDR.
MATERIALS AND METHODS Animals Primiparous (n = 167) and multiparous (n = 716) suckled beef cows managed to be in moderate BCS were used in this study. A total of 5 replications from 3 locations over 2 yr constitute the data set: Feldun Purdue Agricultural Center (FPAC; one replication), Animal Sciences Research and Education Center (ASREC; replications 1 and 2), and Southern Indiana Purdue Agricultural Center (SIPAC; replications 1 and 2). Both FPAC and ASREC were spring-calving herds, whereas SIPAC was a fall-calving herd. Table 1 presents a replication- and treatmentdependent characterization of cattle used in this study.
Treatments All cows were handled in accordance with procedures approved by the Purdue Animal Care and Use
84 Committee. Within replication, cows were stratified by breed, parity, and days postpartum (DPP) and then assigned to treatment. All cows were enrolled in the 5-d CO-Synch protocol (Figure 1) that consisted of administration of 100 μg of GnRH (Cystorelin, Merial, Duluth, GA) on d 0 and 2 doses of PGF2α (Lutalyse, Zoetis Animal Health, Kalamazoo, MI) given between 2 and 10 h apart on d 5. Variation in timing of PGF2α administrations was the result of logistical constraints at some locations. However, it has previously been demonstrated that PGF2α administration at either a 2-, 8-, or 12-h interval is equally effective in the 5-d CO-Synch protocol (Souto et al., 2009). In the present study, treatment consisted of either the inclusion of exogenous progesterone (CIDR insert; CDR; Eazi-Breed CIDR, Zoetis Animal Health; n = 445) or no exogenous progesterone (NCDR; n = 438) during the 5 d between the first GnRH injection and initial PGF2α. On d 8, 72 h after the initial PGF2α injection, all cows were TAI concurrent with GnRH administration (100 μg; Cystorelin, Merial). Cows were handled as commingled groups throughout the experiment and were inseminated at random relative to treatment. Between 7 and 10 d following TAI, fertile bulls were placed with the cows for the remainder of the breeding season (approximately 60 d). Pregnancy diagnosis was performed between 32 and 38 d after TAI using transrectal ultrasonography (variable megahertz linear array transducer, MicroMaxx, Sonosite, Bothell, WA) and used to calculate TAI pregnancy rates. A second pregnancy diagnosis was conducted via transrectal ultrasonography between 32 and 38 d after the conclusion of the breeding season to calculate end-of-season pregnancy rates.
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SIPAC replication 1) and again on d 0 to estimate the proportion of cows that had resumed ovulation-cycle activity at the initiation of the ovulation synchronization protocol. Blood samples were collected via coccygeal venipuncture in 6-mL tubes containing EDTA (BD Vacutainer; Becton Dickinson, Franklin Lakes, NJ) and immediately placed on ice. Samples were centrifuged within 8 h after collection at 1,750 × g for 25 min at 4°C; plasma was recovered, transferred to 5-mL polystyrene tubes, and frozen at −20°C until it was analyzed for progesterone concentration. Progesterone concentration was determined using a commercially available RIA kit (CoatA-Count, Siemens Medical Solutions Diagnostics, Los Angeles, CA). For 4 assays, the average intraassay CV was 2.1% and the interassay CV for pooled plasma samples containing 0.19 and 6.35 ng/mL of progesterone were 6.4 and 7.2%, respectively. The average sensitivity was 0.04 ng/mL (95% CI). For assessment of reproductive status, cows that had progesterone concentrations ≥1 ng/mL in either or both plasma samples were considered to have resumed regular estrous-cycle activity.
Data and Statistical Analysis Timed-AI pregnancy rate was defined as the proportion of all treated cows that were determined to be pregnant as a result of TAI. Breedingseason pregnancy rate was the proportion of all treated cows that became pregnant to TAI or bull exposure.
Cows diagnosed as pregnant to timedAI at initial pregnancy detection that were subsequently diagnosed as not pregnant to TAI at final pregnancy detection were classified as having embryonic loss. Embryonic-loss rate was calculated as the number of cows that aborted divided by the number of cows diagnosed as pregnant to TAI at initial pregnancy detection. For statistical analysis, cows were classified as either primiparous (2 yr of age) or multiparous (≥3 yr of age). The GLIMMIX procedure of SAS was used to analyze all categorical data. There were no significant treatment × year or treatment × locations interactions (P > 0.10) for any of the variables measured; therefore, data within each location and year were analyzed as an individual replication, for a total of 5 replications. For dependent variables of interest, the initial model included the fixed main effects of treatment, parity, season, and reproductive status as well as all appropriate interactions, and replication was included as a random effect. Interactions with a significance value of P > 0.15 were removed from the model in a stepwise manner to derive the final reduced model for each variable. As the effects of AI technician and AI sire were confounded within replication, the effect of AI sire, AI technician, treatment, and the appropriate interactions were evaluated first within replication. Although technician and AI sire were significant within some replications, there were no AI sire or AI technician × treatment interactions (P > 0.15); thus,
Reproductive Status Blood samples were collected on either d −11 (ASREC replication 2 and SIPAC replication 2) or d −7 (FPAC, ASREC replication 1, and
Figure 1. Experimental protocol used to synchronize ovulation in suckled beef cows. Cows were administered the 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone (controlled internal drug-release insert; CIDR). GnRH = gonadotropin-releasing hormone; PGF2α = prostaglandin F2α.
85
5-day CO-Synch with or without exogenous progesterone
these variables were subsequently removed. In an ancillary analysis, cows were classified into 6 groups based on number of DPP at d 0 (<41, 41–50, 51–60, 61–70, 71–80, and >80) to analyze the effect of DPP on cyclicity as well as pregnancy and embryonicloss parameters previously described. The initial model included the main effects of treatment and DPP grouping as well as the appropriate interac-
tion, with replication included as a random effect. The treatment × DPP grouping interaction was removed if not significant (P > 0.15). Differences were considered to be significant when P ≤ 0.05 and a tendency when 0.05 < P ≤ 0.10.
RESULTS AND DISCUSSION The objective of this study was to determine whether TAI pregnancy
rates differed in beef cows synchronized with the 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone. As the use of a CIDR represents the greatest pharmaceutical cost of this ovulation synchronization protocol, the ability to remove this product while maintaining similar TAI pregnancy may increase the adoption of ovulation synchronization and AI in the beef industry. Results of the present
Table 2. Timed AI, overall breeding-season pregnancy rates, and embryonic-loss rates in beef cows synchronized for ovulation with a 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone Treatment1 CDR, % (no./no.)2
Item Timed-AI pregnancy rate Treatment Parity4 Primiparous Multiparous Reproductive status5 Cyclic Anestrous Breeding-season pregnancy rate Treatment Parity Primiparous Multiparous Reproductive status Cyclic Anestrous Embryonic-loss rate6 Treatment Parity Primiparous Multiparous Reproductive status Cyclic Anestrous
62.3 (276/443)a 69.0 (60/87)a 60.7 (216/356)a 63.5 (241/380)a 55.4 (31/56) 90.5 (402/444) 83.9 (73/87) 92.2 (329/357) 91.0 (345/379) 85.7 (48/56) 2.5 (7/276) 3.3 (2/60) 2.3 (5/216) 2.9 (7/241) 0 (0/31)
NCDR, % (no./no.)2
50.7 (221/436)b 46.3 (37/80)b 51.7 (184/356)b 49.7 (187/377)b 57.4 (32/56) 89.9 (393/437) 83.8 (67/80) 91.3 (326/357) 90.5 (341/377) 89.1 (49/55) 3.2 (7/221) 2.7 (1/37) 3.3 (6/184) 3.2 (6/187) 3.2 (1/31)
Combined, % (no./no.)2
56.5 (497/879) 58.1 (97/157) 56.2 (400/712) 56.5 (428/757) 56.3 (63/112) 90.2 (795/881) 83.8 (140/167)y 91.7 (655/714)z 90.7 (686/756) 87.4 (97/111) 2.8 (14/497) 3.1 (3/97) 2.8 (11/400) 3.0 (13/428) 1.6 (1/62)
P-value3
0.05 0.35 0.76 0.94 0.004 0.14 0.68 0.79 0.52
Within a row, means lacking a common superscript differ due to treatment (P ≤ 0.05). Within a column, means lacking a common superscript differ (P ≤ 0.05). 1 A 5-d CO-Synch ovulation synchronization protocol with (CDR) or without (NCDR) inclusion of a controlled internal drug-release insert. 2 Results are presented as the proportion of cows pregnant within treatment and classification. The number of cows pregnant divided by the number of cows in which pregnancy status was determined is presented in parentheses. 3 Main effects of treatment, parity, and reproductive status. 4 A treatment × parity interaction was observed (P = 0.08; Figure 2). 5 A treatment × reproductive status interaction was observed (P = 0.14; Figure 3). 6 Of cows diagnosed as pregnant to timed AI at initial pregnancy detection, the proportion of cows that were diagnosed as open or not pregnant to timed AI at final pregnancy detection. a,b y,z
86 study demonstrate that removal of exogenous progesterone in the 5-d approach reduced TAI pregnancy rates and thus is not recommended. Reproductive status was analyzed in 869 of the 883 cows enrolled in the study, with 87.1% of cows determined to be cyclic at treatment initiation (Table 1). Across replications, the proportion of cyclic cows ranged from 78.8 to 96.0%. Reproductive status was not different between treatments (P = 0.98; 87.2 vs. 87.1% for CDR and NCDR, respectively) and was not affected by parity (P = 0.62; 88.9 and 86.7% for primiparous and multiparous, respectively). It has been reported that the average postpartum interval to first estrus is less than 60 d in adequately nourished cows (Bailey et al., 1988; Houghton et al., 1990). Because 77.3% of cows in the current study were greater than 60 DPP at the initiation of ovulation synchronization, the large proportion of cyclic cows was not surprising. We acknowledge that the low proportion of anestrous females in this study is a limitation of the data set, as one potential benefit of progesterone inclusion in an estrous synchronization protocol is stimulating estrous cycles in anestrous females (Fike et al., 1997; Perry et al., 2004). The proportion of cyclic cows at treatment initiation was unexpectedly not affected by parity. Although these results are supported by Lamb et al. (2001), previous studies have demonstrated that primiparous cows are more likely to be anestrous at the initiation of the breeding season when compared with multiparous females (Short and Adams, 1988; Short et al., 1990; Stevenson et al., 2003a; Larson et al., 2006). The lack of difference in cyclicity relative to parity in the current study is likely a result of primiparous females averaging 80 DPP at treatment initiation, which was 10 d more than multiparous females. Timed-AI pregnancy rate, breedingseason pregnancy rate, and embryonic-loss rate in relation to treatment, parity, and reproductive status are located in Table 2. Timed-AI pregnancy rates were greater in CDR-
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Figure 2. Effect of the 5-d CO-Synch ovulation synchronization protocol with (CDR) or without (NCDR) exogenous progesterone (controlled internal drug-release insert) on timed-AI pregnancy rates of suckled beef cows at each location (overall P-value = 0.05): Feldun Purdue Agricultural Center (FPAC; one replication), Animal Sciences Research and Education Center (ASREC1 and ASREC2 for replications 1 and 2, respectively), and Southern Indiana Purdue Agricultural Center (SIPAC1 and SIPAC2 for replications 1 and 2, respectively).
than NCDR-treated cows (P < 0.001; Table 2 and Figure 2). It has been previously demonstrated that failing to include a CIDR insert in the 7-d CO-Synch protocol reduces pregnancy success in beef cows (Lamb et al., 2001; Stevenson et al., 2003b; Larson et al., 2006), which is likely due in part to expression of premature estrus in CO-Synch protocols. To this point, Dejarnette et al. (2001a,b) reported that in the 7-d protocol, failure to include a CIDR resulted in 8 to 10%
of cows displaying premature estrus. Premature estrus expression likely occurs more frequently in cows that fail to respond to GnRH. Yet, it has been hypothesized that 2 fewer days between GnRH and PGF2α in the 5-d CO-Synch protocol when compared with the 7-d CO-Synch protocol may reduce the occurrence of premature estrus. However, estrous expression was not recorded in this study. The main effects of parity and reproductive status did not affect preg-
Figure 3. Treatment × parity interaction (P = 0.08) for timed-AI pregnancy rates in beef cows that had ovulation synchronized using the 5-d CO-Synch protocol with (CDR) or without (NCDR) exogenous progesterone (controlled internal drug-release insert). Across parity, bars lacking a common letter differ (P ≤ 0.05).
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Within a row, means lacking a common superscript differ due to treatment (P ≤ 0.05). Within a row, means lacking a common superscript tend to differ (0.05 < P ≤ 0.10). 1 There were no interactions (P > 0.15) between days postpartum classification and treatment relative to reproductive response variables. 2 Days postpartum at initiation of ovulation synchronization. 3 Results are presented as the proportion of cows within treatment and classification. The number of cows with a positive response for the variable of interest divided by the number of cows in which status was determined is presented in parentheses. 4 Of cows diagnosed as pregnant to timed AI at initial pregnancy detection, the proportion of cows that were diagnosed as open or not pregnant to timed AI at final pregnancy detection. y,z
92.6 (249/269) 58.8 (160/272) 91.2 (250/274) 2.5y (4/160) 90.5 (134/148) 50.3 (74/147) 87.1 (128/147) 8.1z (6/74) 68.6 (57/83) 55.9 (47/84) 86.9 (73/89) 2.1y (1/47) 66.7 (42/63) 52.3 (33/63) 90.4 (57/63) 3.0y (1/33) 54.9 (28/51) 56.8 (29/51) 88.2 (45/81) 0y (0/29) Cyclicity Timed-AI pregnancy rate Breeding-season pregnancy rate Embryonic-loss rate4
a–c
<0.001 0.57 0.46 0.09 96.9 (247/255) 58.8 (154/262) 92.4 (242/262) 1.3y (2/154)
P-value >80
c
71–80
b b
61–70 51–60
a a
a
41–50 <41 Item
Days postpartum,2 % (no./no.)3
nancy to TAI (P ≥ 0.37). Although the number of anestrous and primiparous females was limited in this study, these results are still surprising given the ability of a CIDR to induce cyclic status and the propensity for primiparous females to be anestrous at the initiation of the breeding season. However, we acknowledge that GnRH alone can also induce cyclicity in anestrous females. Even though it has been reported that response to GnRH is improved when progesterone concentrations are suppressed (Perry and Perry, 2009), response to GnRH in anestrous females is variable, reported from 16.5% (Stevenson et al., 2000) to 88.9% (Geary et al., 2000). Thus, exposing cows to progesterone via CIDR in combination with GnRH is more consistently effective in stimulating cyclicity than GnRH alone (Stevenson et al., 2003a). In addition to the 7-d CO-Synch protocol being less effective in stimulating estrous-cycle activity in anestrous females when compared with the 7-d CO-Synch + CIDR protocol (Stevenson et al., 2003a), reduced pregnancy rates in the 7-d CO-Synch protocol is in part due to premature expression of estrus of cyclic females before TAI (Stevenson et al., 2000; Dejarnette et al., 2001a,b). As previously stated, it was hypothesized that the 2-d difference in duration of the 5- and 7-d protocols may reduce the number of cows displaying premature estrous before TAI. Although this variable was not directly assessed, results from this study demonstrate that as in the 7-d CO-Synch protocol, exogenous progesterone administration improves pregnancy rates to TAI in the 5-d CO-Synch protocol. There was a tendency for a treatment × parity interaction (P = 0.08) for TAI pregnancy rates (Figure 3). Although CDR obtained greater (P ≤ 0.01) TAI pregnancy rates than NCDR in both primiparous and multiparous groups, difference between treatments was greater in primiparous females (69.0 vs. 46.3% for CDR and NCDR, respectively) than multiparous females (60.7 vs. 51.7% for CDR and NCDR, respectively). Because
Table 3. Effect of days postpartum on reproductive parameters of beef cows synchronized for ovulation with a 5-d CO-Synch protocol with or without the inclusion of exogenous progesterone1
5-day CO-Synch with or without exogenous progesterone
88 cyclicity was similar between primiparous and multiparous cows, this interaction is not easily explained; however, the number of primiparous and anestrous females enrolled in this study are acknowledged as a limitation of the data set. Timed-AI pregnancy rate was not affected by DPP category (P = 0.57; Table 3). However, a seasonal effect on TAI pregnancy success was observed (P < 0.001; Figure 2) independent of treatment, parity, and reproductive status; spring-calving cows (ASREC and FPAC) had greater TAI pregnancy rates than fall-calving cows (SIPAC; 65.7 vs. 46.4%, respectively). This seasonal or location effect on TAI pregnancy rates was somewhat surprising because fall-calving cows had the longer postpartum interval and a larger proportion of cyclic females at treatment initiation. This is likely because of differences in production systems; fall-calving cows were sustained on stockpiled endophyteinfected fescue before the breeding season, whereas the other 3 springcalving herds had greater access to legumes and cool-season grasses. Previous studies have demonstrated that grazing endophyte-infected fescue may exhibit suppressed first-service AI conception rates in heifers (Washburn et al., 1989) and calving rates in cows (Gay et al., 1988; Washburn and Green, 1991). Reduced fertility in endophyte-fed females may be a result of reduced implantation rates, as Varney et al. (1987) reported in female rats fed an endophyte seed diet. Although CDR improved pregnancy to TAI when compared with NCDR, overall breeding-season pregnancy did not differ as a result of estrous synchronization treatment (P = 0.94; Table 2). Late embryonic loss in this study was 2.8%, and although not different due to treatment (P = 0.68), embryonic loss was similar to that reported by Stevenson et al. (2015). Similar to the current study, Galvão et al. (2004) reported no differences of embryonic loss between d 27 and 41 after AI when comparing dairy cows synchronized with either the 7-d
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CO-Synch or 7-d CO-Synch + CIDR protocol.
IMPLICATIONS Inclusion of exogenous progesterone improved pregnancy rates in cows synchronized for ovulation with the 5-d CO-Synch protocol. Moreover, the increase of 11.6 percentage units in TAI pregnancy rates for cows treated with exogenous progesterone likely more than offsets the cost of progesterone inserts for the entire herd. Thus, to optimize TAI pregnancy rates in beef cows synchronized with the 5-d CO-Synch protocol, use of exogenous progesterone is recommended.
ACKNOWLEDGMENTS The authors extend their appreciation to Zoetis Animal Health for donation of CIDR inserts and prostaglandin F2α (Lutalyse), as well as to B. Defreese, J. Holmes, L. Houghton, J. Tower, and R. Huntrods for providing assistance with data collection.
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