A high dose of initial GnRH increased ovulatory response and fertility in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol

The objectives of this study were to investigate the effect of presynchronization or dose of GnRH on ovulatory response to initial GnRH, estrus expression and reproductive outcomes in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol. Heifers were fitted with a collar-mounted automated activity monitoring system on Day -5 and were assigned randomly to one of three groups: 1) G100 (n = 111), a 5-d CO-Synch plus PRID protocol with administration of 100 μg of GnRH at the time of PRID insertion (Day 0), 500 μg of cloprostenol (PGF) at the time of PRID removal (Day 5) and again 24 h later (Day 6); 2) G200 (n = 112), same as G100 except 200 μg GnRH was administered on Day 0; 3) P10 (n = 111), PRID + PGF on Day -5 followed by a 5 d CO-Synch with administration of 100 μg of GnRH on Day 0, PGF at the time of PRID removal (Day 5) and again 24 h later (Day 6). Approximately 72 h after PRID removal (Day 8), all heifers were timed-inseminated (TAI) and concurrently 100 μg of GnRH was administered to those not exhibiting estrus. All inseminations were done by one technician using either sex-sorted (n = 265) or conventional (n = 69) frozen-thawed semen. Transrectal ultrasonography was done to determine ovarian cyclicity and normalcy of the reproductive tract, ovarian dynamics and pregnancy. All heifers were cyclic and ovulatory response to initial GnRH was greater (P < 0.01) in G200 (51.8%) and P10 (47.7%) compared to G100 (27.9%). Estrus expression rate tended to be greater (P = 0.08) in G100 (93.7%) compared to G200 (85.7%) and intermediate in P10 (89.2%). Expression of estrus was associated positively with P/AI at 45 d post-TAI (P < 0.01; 70.2 vs. 31.4% for heifers expressing or not expressing estrus). Heifers in the G200 group had greater P/AI at 30 (P < 0.01) and 45 (P = 0.01) d post-TAI (79.5 and 75.9%, respectively) compared to those in G100 (63.1 and 60.4%) or P10 (64.0 and 62.2%) groups. Pregnancy loss did not differ among treatment groups (overall 3.9%). Results indicate that increasing the dose of the initial GnRH from 100 to 200 μg resulted in increased ovulatory response and improved P/AI in Holstein heifers subjected to a progesterone based 5-d CO-Synch protocol. Although heifers presynchronized with a combination of PRID and PGF had an increased ovulatory response to the initial GnRH, P/AI did not differ from the standard progesterone based 5-d CO-Synch protocol.

Effect of initial GnRH and time of insemination on reproductive performance in cyclic and acyclic beef heifers subjected to a 5-d Co-synch plus progesterone protocol

This study evaluated the effect of initial GnRH and timing of AI in a 5-d Co-synch plus CIDR (device containing 1.38 g of progesterone) protocol on pregnancy per AI (P/AI) and pregnancy loss in beef heifers. A secondary objective was to determine if the effect of initial GnRH on reproductive performance was influenced by cyclicity. Crossbred beef heifers (n = 1068; 301-514 kg of body weight, and 13-15 mo of age) at three locations were assigned to either a 5-d Co-synch plus CIDR protocol with (CIDR5G) or without (CIDR5NG) an initial injection of 100 μg of GnRH at CIDR insertion (Day 0). All heifers received a single dose of 500 μg of cloprostenol at CIDR removal (Day 5) and were divided into two groups to receive GnRH and TAI at either 66 or 72 h (Day 8) after CIDR removal. All heifers were inseminated by one technician with frozen-thawed semen from 1 of 4 sires available commercially. Transrectal ultrasonography was performed on Day 0 to determine cyclicity (presence of CL) and normalcy of the reproductive track, and 27 d after TAI to determine pregnancy status. Non-pregnant heifers (n = 470) were assigned to either a CIDR5G or a CIDR5NG protocol with TAI at 72 h after CIDR removal. Twelve days after second AI, heifers were exposure to bulls for 20 d and pregnancy diagnoses were performed approximately 30 d after second TAI and 60 d after bulls were removed to diagnose bull pregnancies and determine pregnancy loss rate. The percentage of acyclic heifers was 20.3%. Overall P/AI after first TAI was 55.6% (594/1068) and did not differ between CIDR5G and CIDR5NG (56.1 vs. 55.1%), or between TAI66 and TAI72 (55.8 vs. 55.4%). However, cyclic heifers were more likely to become pregnant than acyclic ones (59.3 vs. 41.2%; P < 0.01). Moreover, acyclic heifers subjected to the CIDR5NG had fewer P/AI than those subjected to CIDR5G (P < 0.01). Overall P/AI after resynchronization was 55.1% and did not differ between CIDR5G and CIDR5NG (51.3 vs. 59.0%). Overall pregnancy loss after first and second TAI were 3.0% (18/594) and 3.9% (8/205), respectively. When pregnancy loss data were combined, synchronization protocol (4.1 vs. 2.3% for CIDR5NG and CIDR5G; P = 0.01), cyclicity (5.8 vs. 2.9% for acyclic and cyclic; P = 0.03) and the interaction between synchronization protocol and cyclicity (P = 0.04) were significant. The overall cumulative pregnancy at the end of the breeding season was 94.2% (1006/1068); acyclic heifers were less likely to be pregnant at the end of the breeding season (88.4 vs. 95.8%; P < 0.01). In summary, the initial GnRH administration in a 5-d Co-synch plus CIDR protocol that includes a single PGF treatment is necessary in acyclic beef heifers to optimize P/AI, but not in cyclic heifers. Moreover, omission of initial GnRH was associated to greater pregnancy losses, particularly in acyclic heifers. Timing of AI did not affect P/AI.

Risk factors associated with dystocia in a tie stall dairy herd

The aims of the study were to: (1) investigate factors affecting calf birth weight (CBW) and gestation length (GL); and (2) determine risk factors associated with dystocia in 1019 Holstein heifers and cows in a tie stall dairy herd. Calf sex (CS), sire, and GL were related to CBW in primiparous and multiparous cows, with no significant effect of season, age of primiparous cows (AGE) or days in milk (DIM) of multiparous cows at conception. Gestation length was affected by CS in primiparous, with a shorter GL for female versus male calves (275.7 ± 0.5 vs. 278.3 ± 0.4; P < 0.001). Also, GL was shorter in multiparous cows that calved during the cold season compared to those that calved in mild or warm seasons. Primiparous cows had a higher prevalence of dystocia compared to multiparous cows (32.1 vs. 8.5%; P < 0.001), but it was highly variable depending on sire (24.4%–60.0% for primiparous and 0%–21.1% for multiparous). In conclusion, CS, sire, and GL were related to CBW, whereas GL was affected by CS in primiparous and season in multiparous. The CBW was the major factor affecting dystocia in primiparous cows, whereas sire and twin pregnancies were factors related to dystocia in both primiparous and multiparous cows.

12 INITIAL GONADOTROPIN-RELEASING HORMONE TREATMENT INCREASED PREGNANCY PER TIMED INSEMINATION ONLY IN ACYCLIC BEEF HEIFERS SUBJECTED TO A 5-DAY CO-SYNCH PROTOCOL

We have shown that inclusion of initial gonadotropin-releasing hormone (GnRH) in a 5-day Co-synch protocol is unnecessary to achieve acceptable pregnancy rates in dairy heifers (2011 Theriogenology 76, 578). This study determined the efficacy of a modified (without initial GnRH) 5-day Co-synch protocol for timed AI (TAI) and the effect of interval from progesterone device removal to TAI on pregnancy per TAI (P/TAI) in acyclic and cyclic beef heifers. Heifers (n = 1062; 302 to 515 kg of body weight, and 13 to 15 months of age) at 2 locations were assigned to either a 5-day Co-synch protocol with (control) or without (modified) an initial injection of 100 μg of GnRH (Fertagyl; Merck Animal Health, Kenilworth, NJ, USA) at progesterone device (CIDR; Zoetis Animal Health, Florham Park, NJ) insertion (Day 0). All heifers received a single dose of 500 μg of cloprostenol (Estrumate; Merck Animal Health) at CIDR removal (Day 5) and were divided into 2 groups to receive GnRH and simultaneously TAI at either 66 or 72 h (Day 8) after CIDR removal. All heifers were inseminated by one technician with frozen-thawed semen from 1 of 4 commercially available sires. Ovarian ultrasonography was performed on Day 0 to determine cyclicity (presence of corpus luteum) and normalcy of the reproductive track, and on Day 35 (27 days after TAI) to determine pregnancy status. Data were analysed using the PROC GLIMMIX in SAS (SAS Institute Inc., Cary, NC, USA). The CIDR retention rate was 98%; P/TAI in heifers that lost the CIDR was 39%. Pregnancy per TAI [least squares means (n)] did not differ (P > 0.05) among sires [48 (235), 51 (318), 52 (274), and 53% (235)], location [57 (330) v. 53% (732)], timing of TAI [52 (533) v. 50% (529) for 66 and 72 h], or treatment groups [48 (525) v. 53% (537) for control and modified groups]. A total of 226 (21%) heifers were acyclic; P/TAI was lower in acyclic heifers compared with that in those cyclic (P < 0.01; 43 v. 59%). Administration of GnRH at CIDR insertion increased P/TAI in acyclic heifers (P < 0.01; 50 v. 35% for control and modified groups) but did not affect P/TAI in those that were cyclic at initiation of protocol (P > 0.05; 57 v. 62% for control and modified groups). In conclusion, timing of TAI did not affect fertility. However, administration of initial GnRH increased P/TAI by 15 percentiles in acyclic females, but as previously shown in Holstein heifers, initial GnRH was unnecessary to achieve acceptable P/TAI in cyclic beef heifers subjected to a 5-days Co-synch protocol. This study was supported by Alberta Agriculture and Forestry, Intervet Canada Corp., and collaborative beef producers.

208 SUPEROVULATORY RESPONSE AND EMBRYO PRODUCTION IN HOLSTEIN COWS FED DIETS ENRICHED IN OLEIC, LINOLEIC, OR α-LINOLENIC ACID

Early embryonic development is enhanced in Holstein cows fed diets enriched in linoleic and α-linolenic acids compared to those fed a diet enriched in stearic fatty acid (Thangavelu et al. 2007; Theriogenology 68, 949–957). A positive effect of oleic acid on oocyte competence in vitro has been reported (Aardema et al. 2011; Biol. Reprod. 85, 62–69), but the influence of oleic acid on early embryonic development has not been investigated. Therefore, our objective was to evaluate the effects of diets enriched in oleic, linoleic, or α-linolenic acid on superovulatory response and embryo production. Non-lactating Holstein cows were blocked by parity and bodyweight, and assigned to one of three diets supplemented with canola (CAN, n = 8; 62% oleic acid), sunflower (SUN, n = 7; 73% linoleic acid), or flax (FLX, n = 8; 57% α-linolenic acid). Cows were individually offered hay (9.4 kg) and concentrate mixture (4.1 kg) supplemented with one of the three rolled oilseeds (~8% of dietary dry matter). After a minimum of 21 days of diet adaptation, cows were given FSH (300 mg total dose, eight 12-hourly injections), artificially inseminated twice, 12 h apart, with semen of the same sire and ova/embryos recovered non-surgically 7.5 days post-insemination. Once started on a diet, cows continued to receive the same diet until the end of the experiment. Thirty-five collections (flushing) were performed (CAN: 12, SUN: 11 and FLX: 12) and data were analysed using the GENMOD procedure of SAS (SAS Institute Inc., Cary, NC, USA); results are presented as mean ± s.e. Number of corpora lutea (12.8 ± 2.6, 14.5 ± 1.2 and 13.1 ± 1.5), anovulated follicles (3.0 ± 1.4, 2.0 ± 1.1 and 2.6 ± 0.9), and total ova/embryos (7.5 ± 2.0, 8.6 ± 1.7 and 7.3 ± 1.2) did not differ (P > 0.05) for CAN, SUN, and FLX treatment, respectively. Cows fed SUN tended (P = 0.06) to produce more transferable embryos (6.1 ± 1.7) than those fed CAN (4.3 ± 1.5), but did not differ from those fed FLX (4.8 ± 1.3). There were fewer (P < 0.05) unfertilized ova in cows fed SUN (0.6 ± 0.5) than in those fed either CAN (1.3 ± 0.6) or FLX (1.8 ± 0.9). Conversely, cows fed FLX had fewer (P < 0.05) degenerated embryos (0.7 ± 0.4) compared to those fed either CAN (1.9 ± 0.6) or SUN (1.9 ± 0.5). The number of expanded blastocysts was greater (P < 0.05) in cows fed CAN (1.08 ± 0.57) than in those fed FLX (0.25 ± 0.25), but it was not different from those fed SUN (0.90 ± 0.36). In summary, the type of dietary fatty acid did not affect superovulatory response, but a diet enriched in oleic acid resulted in more expanded blastocysts, whereas a diet enriched in linoleic acid significantly reduced the number of unfertilized ova and numerically increased transferable embryos. The diet enriched in α-linolenic acid resulted in fewer degenerated embryos. This study was supported by Alberta Meat and Livestock Agency, Alberta Milk, and Alberta Innovates-BioSolutions.