The primary controller of weaned pig output is the successful breeding of enough females in the breeding week. The number of females available for breeding is dependent on the number of sows weaned sows and service-ready gilt availability. Primiparous (P1) sows often have longer wean-estrus intervals (WEI) and increased anestrus; ensuring sufficient gilts and sows are available may require control of estrus. Stimulating estrus requires appropriate boar contact or when this is not sufficient, administration of gonadotrophins. If gonadotrophins are used expect estrus 4 to 6 d later and it is usual to breed at the induced estrus. If there is a problem of non-response the most likely cause is the females had a missed estrus are in their luteal phase. This can be resolved by feeding altrenogest for 18 d; expect cyclic animals to return 5 to 8 d later. The estrus response can be improved by gonadotrophin treatment at the end of altrenogest feeding. Female fertility is optimized by ensuring sperm deposition in the period 0 to 24 h before ovulation. This degree of accuracy may require control of ovulation by treatment with human chorionic gonadotrophin (ovulation 40-44 h later) or gonadotrophin releasing hormone (ovulation 36-40 h later). Knowing time of ovulation will allow use of other breeding technologies such as use of lower sperm numbers per dose and single inseminations.
Kirkwood, Roy N. and Rensis, Fabio De
"Control of Estrus in Gilts and Primiparous Sows,"
The Thai Journal of Veterinary Medicine: Vol. 46:
1, Article 1.
Available at: https://digital.car.chula.ac.th/tjvm/vol46/iss1/1