Comparison of Single, Fixed-Time Artificial Insemination in Gilts Using Two Different Protocols to Synchronize Ovulation

In order to efficiently have a consistent supply of service-ready gilts available to incorporate into each batch of breeding sows, it is necessary to manipulate the timing of estrus and possibly the timing of ovulation of gilts. Estrus can be synchronized by the withdrawal of altrenogest after at least 14 days of treatment. It is possible that protocols developed to induce ovulation, and therefore allow fixed-time artificial insemination (FTAI), can improve the predictability of gilt breeding. This study investigated the effect of two FTAI protocols in gilts on reproductive performance and timing of farrowing and piglet weaning weight compared to gilts bred based on signs of estrus after cessation of altrenogest. Puberty was induced in gilts, followed by treatment with altrenogest. Following altrenogest withdrawal, 180 gilts were assigned to one of three treatment groups. Group 1 gilts (LUT, n = 62) were treated with 600 IU equine chorionic gonadotropin 24 h after altrenogest withdrawal and 5 mg porcine luteinizing hormone (pLH) 80 h later, followed by a single FTAI 36 h after pLH. Group 2 gilts (TRI, n= 61) received 2 mL of a gonadotropin-releasing hormone agonist, triptorelin acetate, intravaginally 6 d after altrenogest withdrawal and were bred by a single FTAI 24 h later. Group 3 gilts (CON, n = 57) were observed for estrus and bred twice by AI, 24 h apart. LUT and TRI gilts farrowed closer together (2.4 ± 1.6 and 2.9 ± 1.2 d(days), respectively) compared to CON gilts (4.5 ± 3.3 d). Piglets in LUT were 80 g (p < 0.001) heavier and piglets in TRI were 64 g (p < 0.05) heavier at weaning than CON piglets, when controlling for birth weight. Results indicate that FTAI might be useful as a means of minimizing the time from the first to the last gilt farrowing in a breeding batch of gilts. However, modifications of the protocols may be required to ensure optimum farrowing rates and litter size.

58ESTRUS SYNCHRONIZATION OF DAIRY GOATS UTILIZED AS RECIPIENTS FOR CAPRINE NUCLEAR TRANSFER EMBRYOS

The timing of estrus synchrony between donor and recipient does is an important consideration in an embryo transfer program. Experiments were conducted to determine the optimal time of estrus synchrony between donor and recipient dairy goats used in a commercial nuclear transfer (NT) program. Donor and recipient synchronization was achieved by implanting either a 3-mg norgestomet ear implant (Crestar®, Intervet Int. B.V., Boxmeer, Holland) or a 300-mg progesterone vaginal implant (CIDR-G®, Pharmacia and Upjohn Ltd. Co., Auckland, NZ) on Day 0. A single 5mg intramuscular injection of prostaglandin (Lutalyse®, Pharmacia and Upjohn, Kalamazoo, MI, USA) was administered on Day 7. Recipients received a single 200–500IU intramuscular injection of PMSG (Calbiochem, LaJolla, CA, USA) on Day 13. Alternatively, starting on Day 12 donors received twice daily intramuscular injection (64mg/day) of FSH (Folltropin®, Vetrepharm, Ontario, Canada) over four consecutive days. On Day 15 the implants were removed from both donors and recipients and the animals were mated several times daily to vasectomized bucks over two consecutive days. In Experiment 1, estrus synchrony or asynchrony was achieved by removing the implant from recipients at the same time or 12h later than donors, respectively. In Experiment 2, only estrus asynchrony was utilized and was achieved by removing the implant from recipients either 12 or 18h later than donors. In vivo-ovulated MII oocytes surgically recovered from superovulated donors on Day 17 were enucleated and reconstructed with transfected caprine fetal or adult skin cells or transgenic adult skin cells. Couplets were simultaneously fused, activated, and then cultured in SOF/BSA for 48h at 38°C. Two-to-eight-cell NT embryos at 48h post-fusion and activation were surgically transferred to the oviducts of surrogate recipients with similar implant types and PMSG doses. Pregnancies were determined by ultrasonography starting at approximately Day 28 post-fusion and activation and then monitored weekly. In Experiment 1, there were significantly more pregnant asynchronous recipients compared with synchronous recipients (6 of 24 v. 12 of 124 does, respectively). While there were no significant differences, more offspring were produced per embryo transferred to asynchronous recipients compared with synchronous recipients (5 of 135 v. 11 of 690 offspring per embryo transferred, respectively). In Experiment 2, while not significant, there were more pregnant +12-h asynchronous recipients compared with +18-h asynchronous recipients (16 of 72 v. 5 of 36 does, respectively). Again, while there were no significant differences, more offspring were produced per embryo transferred to +12h compared with +18h asynchronous recipients (11 of 424 v. 3 of 224 offspring per embryo transferred, respectively). These results suggest that asynchrony of estrus between recipients and donors is more beneficial in a commercial caprine NT program, and that +12h may be a more optimal period of asynchrony for recipient does receiving NT embryos. Table 1 Summary of recipient estrus synchronization