A gilt’s response to early boar exposure has been shown to be a viable option for estimating her lifetime productivity as a sow. Unfortunately, providing adequate boar exposure at young ages poses several practical and biosecurity issues for many multiplication farms. Boar exposure stimulates the brain to produce gonadotropins which, in turn, stimulate follicles on the ovary to grow and produce estrogen. As estrogen increases the vulva becomes red and swollen and the female will eventually exhibit the standing reflex. The purpose of this study was to determine whether reddening and swelling of the vulva in response to low levels of gonadotropins given to gilts at an early age could be used as a screening tool to estimate her potential longevity. Results from the present study demonstrated that 140 day-old gilts that exhibited any degree of reddening and swelling of the vulva in response to 200 IU of PG600 exhibited retention rates similar to a contemporary group of gilts that exhibited estrus in response to boar exposure. By the end of the third lactation, 62% of the females that entered the farm as replacement gilts were rebred after weaning their third litter in both groups. There was also no difference in farrowing rates or number of pigs born alive between those given low levels of PG600 and their counterparts given boar exposure at 140 days of age. Use of low levels of PG600 and subsequent monitoring of gilts for about 1 week appears to have good potential as a prospective physiological test for sow longevity. In some multiplication systems may be more practical and safer from a biosecurity perspective than providing direct contact with a boar.
Key Findings:
• Sixty-five percent of the gilts that exhibited reddening and swelling of the vulva with 7 days after the low dose of PG600 administered at 140 days of age were still in production after 3 parities.
• This was similar to the 68% of gilts that exhibited estrus within 28 days of boar exposure when it began at the same age (early responders).
• Farrowing rates and number of pigs born alive were similar between gilts responding to low doses of PG600 and early boar exposure.
• Reddening and swelling of the vulva in response to low doses of PG600 administered as early as 140 days of age is an accurate predictor of sow longevity regardless of the neonatal litter size in which they were raised.
