Effects of high temperature stress during gestation on certain aspects of reproduction in the ewe.

Abstract

In this paper are summarized a series of studies dealing with the effect of heat stress during late gestation on reproduction in the ewe. Ewes were stressed in a heat chamber maintained at either 32° C.±1 or 40.5° C.±1 for either 12 or 24 hr. Control ewes were maintained in a similar facility where temperatures did not exceed 24°C.±1. As in earlier studies, fetal dwarfing was observed as an effect of temperature stress during gestation. However, in this study, a significant reduction in the number of lambs born was also observed. In a further study of the mechanism of fetal dwarfing, ewes heat stressed for 12 hr. were essentially intermediate in birth weight and survival between nonstressed ewes and those stressed for 24 hr. These data seem to indicate that the phenomenon is quantitative in nature. Attempts were made to improve birth weight and survival of lambs by improving the nutrition of the ewe. The control rations used approximated the N.R.C. recommendations for protein, and 75% of the N.R.C. recommendations for TDN. Increases above this level did not significantly improve birth weight and lamb survival. Such differences as were observed tended to favor the lower level of feed intake. This tendency for an adverse effect was especially marked with high protein under heat stressed conditions. Data are also presented to indicate a significant reduction in gestation length among heat stressed ewes.