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Effect of Short-Term Elevated Dry-Bulb and Dew-Point Temperature on the Cycling Gilt^1,2,3,

Ohio Agricultural Research and Development Center, Wooster

Abstract

THE environmental conditions required for optimum reproductive performance, and the physiological mechanisms which are affected when the reproducing animal undergoes heat stress, have not been well defined. Warnick et al. (1965) reported that gilts exposed to a dry-bulb temperature of 32.2 C showed abnormal estrual behavior. Teague, Roller and Grifo (1968) found the number of corpora lutea in gilts reduced following exposure to heat stress for one estrous cycle prior to breeding and also reported that normal estrual behavior was affected. Edwards et al. (1968) reported a delay in onset of estrus but no significant effect on ovulation rate of gilts exposed to high ambient temperature.

In the present study gilts were used to investigate the effect of exposure to high ambient temperature and humidity for different lengths of time prior to estrus on the number of corpora lutea formed and on certain physiological measurements.

Experimental Procedure

A single dry-bulb temperature, 33.3 C was maintained in the four compartments of the Animal Environment Laboratory. Dew-point temperature was maintained at a level of 28.9 C in two compartments and at 15.6 C in the remaining two. Such a controlled environment was imposed on Duroc gilts for different lengths of time prior to estrus according to the following scheme: entry into the chambers on day of estrus (0—day), or on days 4, 8, 12 and 16 of the estrous cycle. Two days after first observed estrus during confinement gilts were slaughtered and the entire reproductive tract recovered for examination. Eight animals were assigned to each interval of exposure at each of the two dew-point temperatures and, except for a few minutes at time of bleeding, stayed in the chambers throughout the experimental period.

¹ Approved for publication as Journal Article No. 72–69 by the Associate Director of the Ohio Agricultural Research and Development Center.

² The assistance of C. R. Weaver in the analysis of data is gratefully acknowledged.

³ Data are from a thesis submitted to the Graduate School of The Ohio State University by the senior author in partial fulfillment of the requirements for the M.S. degree.

⁴ Present address: Escola "Luiz de Queiroz," Piracicaba, S. P., Brazil.