EFFECT OF TEMPERATURE ON EARLY EMBRYO SURVIVAL IN GILTS.

Abstract

Two trials were conducted with 66 cross-bred gilts during the late summer in 1960 and 1961, followed by a third trial with 35 gilts and 10 boars during the fall and winter of 1962–63 to study the effect of temperature on ovulation rate and early embryo survival to 25 days postbreeding. During each of the first two trials one group was maintained with natural shade on pasture, a second group was cooled at 60° F. and a third was kept in a heated room at 90° F. beginning 10 days postestrus until 25 days after breeding at the second estrus. One-half of the gilts were switched between the two temperatures at 3 days postbreeding. The average ovulation rate at second estrus for gilts on pasture, 90° F. and 60° F. temperatures was 15.1, 14.9 and 15.5, respectively. Differences were not significant. Conception rate was not different at these temperatures, although some gilts at 90° F. ovulated without showing estrus. Differences in number of live embryos due to all temperature treatments were not significant, although gilts maintained continuously at 90° F. averaged 10.9 embryos compared to 13.5 embryos for gilts at 60° F. Temperature up to 3 days postbreeding had no effect on number of embryos, whereas, gilts maintained at 90° F. from 3 days postbreeding had only 11.3 embryos compared to 13.6 for gilts at 60° F. (P<.05). Gilts in trial 3 maintained at 60° F. had 14.6 corpora lutea compared to 13.6 corpora lutea for those at 90° F. The average number of live embryos at 25 days was 11.7 at 60° F. and 10.4 at 90° F. in gilts bred to boars kept at the two temperatures. There were 0.9 more embryos in gilts bred to boars at 90° F. compared to gilts bred to boars at 60° F., indicating the high temperature did not reduce fertility of the boar. For all three trials there were 1.9 more embryos at 25 days postbreeding in gilts maintained continuously at 60° F. compared to gilts at 90° F. Cooling sows during periods of high temperature, especially soon after breeding, may increase embryo survival and subsequent litter size. It appears that an environmental temperature of 90° F. has less detrimental effect on fertility and embryo survival in gilts than in ewes.