Recent studies at the University of Illinois have explored novel approaches to managing the biological activity of estrus-controlling hormones, the impact they have on ovulation rates and the potential for “fixed time” inseminations.
The first study explores the effectiveness of synchronizing estrus in gilts and the impact it may have on ovulation rates.
Methods to improve estrus induction could impact reproduction through greater numbers and higher quality oocytes (eggs) at ovulation. The payoff would be higher farrowing rates and larger litter size.
The success of techniques that require and utilize oocytes and embryos, such as in vitro fertilization, embryo transfer and nuclear transfer, can be limited by low numbers of poor quality oocytes and embryos.
Most techniques for inducing estrus and ovulation rely on pregnant mare serum gonadotropin (PMSG), with or without human chorionic gonadotropin (hCG). The biological activity of these hormones is difficult to define and control since they contain both follicle-stimulating hormone (FSH) and luteinizing hormone (LH)-like hormone activity and have long half-lives in circulation. Additionally, as with any induction procedure, the results are often inconsistent and have been associated with lower quality oocytes and embryos.
Therefore, two experiments were performed. The first evaluates the optimal dose of FSH and percent LH needed to achieve desired induction, while the second study explores whether administering a slow-release compound could reduce injection frequency.
Experiment 1, involving 128 prepubertal gilts averaging 175 days old, investigated the effect of 10 or 15 units of porcine FSH (pFSH) containing 6, 10 or 15% porcine luteinizing hormone (pLH) on the reproductive response. Nineteen control gilts received PG600. The pFSH dose was divided into six equal injections, given at eight-hour intervals over a two-day period. PG600 was administered in a single injection.
The percentage of gilts induced into estrus was the same for both treatments — an average of 65% (Figure 1). Treatment did alter the proportion of gilts that ovulated and, although not different from PG600, the 15-10 dose induced the greatest percentage of gilts to ovulate, while the 10-15 dose resulted in the lowest ovulation percentage.
Ovulation rate was not influenced by treatment, but gilts receiving 15 units of FSH, and specifically those receiving the 15-10 dose, had the highest number of corpora lutea when compared to the 10-unit doses and PG600. The percentage of gilts with cysts was not different between treatments, but tended to be higher with the 15-unit dose.
Experiment 2 utilized the 15-10 dose from Experiment 1, since ovulation and ovulation rate were numerically the greatest. The experiment tested whether injection in a slow-release compound would allow for a decreased injection frequency.
Sixty-three prepubertal gilts received 15 units of pFSH with 10% pLH in either a single injection or two separate injections at 24-hour intervals. Thirty-three control gilts received PG600.
Estrus induction averaged 66% and was not different between treatments. Treatment did alter the proportion of gilts that ovulated, and although not different from control gilts (82%), a higher percentage of gilts treated with two injections of FSH ovulated (80%) compared to those treated with one injection (56%).
Ovulation rate was influenced by treatment. Gilts receiving two injections had twice the number of ovulations compared to controls (26 vs. 13 CL), but were not different from those receiving one injection (20 CL).
Collectively, these results indicate that the 15-10 dose has the potential to improve ovulation and ovulation rate and, when combined in a slow-release compound, can be effectively used with fewer injections. Further research is needed to determine whether this treatment can improve oocyte and embryo quality and could potentially be used for practical application in the breeding herd.
Researchers: Amy Jackson, Sandra Rodriguez-Zas and Rob Knox, Department of Animal Sciences, University of Illinois.
Novel Hormone Treatment May Lead to Fixed Time AI
Farrowing rate and litter size are limited by the failure to inseminate gilts/sows within the 24 hours before ovulation. Methods to synchronize the time of ovulation could help solve this problem. Synchronization could also reduce reliance on estrus detection and the need for multiple inseminations.
An intravaginal gel delivery system, developed for synchronizing ovulation using gonadotropin-releasing hormone (GnRH), may be the answer. The delivery system was tested in two research studies — one at the University of Illinois, another at a 6,000-sow commercial farm.
In the first experiment, 126 weaned sows received one of the following treatments:
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Two inseminations (AI) at the onset of estrus (control, AI at 2 and 26 hours). These served as the “control” group.
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Two inseminations based on OvuGel, given at 96 hours after weaning (OvuGel-96, AI at 8 and 32 hours), or
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Two AI based on estrus and OvuGel given at onset of estrus (OvuGel-E, AI at 2 and 26 hours).
Sows were checked twice daily for estrus, and transrectal ultrasound was performed twice daily to determine time of ovulation.
For the experiment, 88% of sows displayed estrus within seven days after weaning. The OvuGel-96 treatment reduced the interval from estrus to ovulation and the duration of estrus compared to controls. The OvuGel-E treatment had little effect (Figure 2.)
OvuGel-96 treatment did not improve the fertility of sows that failed to show estrus in the seven days following weaning. Therefore, AI based on OvuGel-96 treatment did not improve farrowing rates or litter size (11.2) compared to controls (10.0). However, for sows that received the treatment but did show estrus, farrowing rates were similar to controls (Figure 3).
In the second experiment, 503 sows in a 6,000-sow commercial herd were assigned to the same treatments used in Experiment 1. In this experiment, estrus within seven days was lower (66%) than in the first experiment. Yet similar to the first experiment, duration of estrus was reduced by 10 hours with OvuGel-96.
Farrowing rates were lower when mating occurred based on OvuGel-96 treatment (58%), compared to farrowing rates of controls mated at estrus (83%). However, similar to the first experiment, for the sows that expressed estrus, the farrowing rates of the OvuGel-96-treated sows were not different from controls (73%).
In fertile sows that showed estrus within the week after weaning and were mated, the lower farrowing rate of the OvuGel-96 treated sows was attributed to the interval from last insemination to ovulation being less than optimal (-28 hours) compared to controls (-24 hours). This would suggest that the timing of the OvuGel treatment or time of insemination might need to be adjusted.
The results of these two studies indicate that when OvuGel is given to fertile sows, estrus and ovulation intervals are shortened and farrowing rates and litter sizes are similar to AI based on estrus. However, the time for both OvuGel administration after weaning and time of AI should be optimized. This methodology could be used to develop “fixed time” AI protocols and eliminate the need for breeding based on estrus detection.
However, before this OvuGel technology can be applied, this methodology needs to be combined with methods that improve the percentage of fertile sows receiving the treatment. This novel hormone delivery system is beneficial for animal welfare in that there is no needle and no stress on the sow or the handler when the hormone is administered.
Researchers: R. Knox, K. Willenburg, S. Rodriguez-Zas, University of Illinois; and D. Gregor and M. Swanson, EIEICo, Radnor PA.
