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Reproductive Performance of Gilts following Heat Stress Prior to Breeding and in Early Gestation¹

Oklahoma Agriculture Experiment Station, Stillwater

Abstract

Three trials were conducted to study the influence of high ambient temperatures prior to breeding and in early gestation on the reproductive performance of gilts. Two environmental chambers were used with one maintained at 23.4° C. continuously and the other elevated to 38.9° C. for 17 hr. daily and lowered to 32.2° C. the remaining 7 hr.

When gilts were exposed to high temperatures the cycle before breeding, the onset of estrus was delayed by over 2 days. However, differences in ovulation rates, number of embryos or embryo size were not significant when compared to gilts maintained in the cool chamber. When gilts were subjected to the environmental chambers 3 to 5 days prior to breeding, no significant differences were found in the cycle lengths, number of corpora lutea, number of normal embryos or embryo size.

Heat stress during the first 15 days post-breeding was more detrimental to productivity than when applied 15 to 30 days postbreeding. Gilts maintained in the hot chamber the first 15 days after breeding tended to have lower conception rates, fewer (P<.01) viable embryos and lower (P<.01) survival rates than either those maintained in the cool chamber or in outside pasture lots. Embryos from gilts stress 1 to IS postbreeding tended to be smaller when examined at 30 days postbreeding but differences were not significant.

Based on these results, heat stress during early gestation is more critical than heat stress prior to breeding. Gilts were more susceptible to high ambient temperatures the first few days after breeding than after implantation had occurred.

¹ Approved as Journal Manuscript No.1697 of the Oklahoma Agricultural Experiment Station. Project 808 in cooperation with Regional Swine Breeding Laboratory, U.S.D.A., A.R.S., A.H.R.D.

² Institute of Animal Sciences and Industry.

³ U.S.D.A., A.R.S., A.H.R.D., Fort Reno Experiment Station.

⁴ Agricultural Engineering Department.

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