Swine Reproduction Papers
PG600 contains a combination of two hormones that have been approved worldwide for use in swine for inducing estrus. Each single dose contains standardized biological activity of PMSG and hCG. The injection stimulates follicles on the ovary to grow, and to produce estrogen, which induces the female to express estrus (standing response) in the presence of a boar. These follicles will eventually ovulate and release eggs during late estrus. For the drug combination to work effectively, gilts must be near the age and weight of natural puberty, but should not have reached puberty. Generally between 50-60% of gilts are induced to express estrus after an intramuscular injection. But success can often vary from as low as 20% to as high as 100%. For those prepubertal gilts that express estrus, most (>90%) show estrus within 4-6 days after the injection. However, if gilts are already cycling and are given PG600, there is a 70% chance that they will grow and ovulate follicles, but will fail to express estrus. Do not immediately give a second injection if gilts fail to respond to the 1st injection. Some gilts actually ovulate after the 1st injection but fail to show estrus and therefore a 2nd injection would only induce new ovulations and result in a greater delay to next estrus. However, for females that are anestrus 3 weeks after the 1st shot, a 2nd shot can be effective at inducing 50% of these gilts into estrus within a week. Administering higher doses is not recommended, since excess hormone can increase the incidence of cystic ovaries. Do not breed gilts at induced estrus due to the occurrence of very low and very high ovulation rates, and frequent failure to maintain pregnancy. For greatest success rates from PG600, know the average or expected age of puberty and treat females approximately 2-3 weeks before the expected onset of pubertal estrus, provide 10 minute boar exposure once daily after administering the hormone to allow accurate detection of estrus, and breed at 2nd or 3rd estrus.
PG600 administered to sows at weaning improves the percent of sows that return to estrus by 20% and reduces the time interval from weaning to estrus by ~1 day. However, generally speaking, farrowing rates and litter sizes are often not improved, even though some reports indicate that greater numbers of pigs are produced when compared to untreated sows. These conflicting reports and the expense of the drug leads us to the conclusion that further research is needed to investigate why greater numbers of sows express estrus, are mated, but then fail to farrow, before PG600 can be recommended for routine use in the sow herd.
PG600 Research at the University of Illinois:
1. PG600 given to sows at weaning induces an earlier return to estrus and delays time of ovulation relative to the onset of estrus. Therefore, slight alterations in the breeding times may be needed to remedy farrowing rate and litter size concerns.
2. In prepubertal gilts, evidence suggests that the subcutaneous PG600 improves estrus and ovulatory responses compared to intramuscular administration. However, in the USA, this is considered extra-label use, and a veterinarian should be consulted.
3. Real-time ultrasound visualization of the female ovaries has the potential to allow more precision in the use of PG600. The rapid assessment of the ovarian status could improve the use and reduce the incidence of misuse of the drug.
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