Diurnal vaginal temperature cycles of Senepol and crossbred beef heifers with different hair coat types and colors under tropical conditions

Abstract

This study evaluated the influence of hair coat type and color on vaginal temperature (VT) regulation of beef heifers. The VT was recorded in five slick-haired, red colored Senepol (SENEPOL); six slick-haired, light-colored crossbred (SLICK); and four wild-type long-haired, light colored crossbred (REGULAR) heifers, every five minutes for four days. Crossbred heifers were obtained from Charbray x Senepol x Charolais crosses. Air temperature and relative humidity were recorded in synchrony with VT for thermal humidity index (THI) calculation. Heifers were kept in a large paddock with access to natural shade. Data were analyzed by the GLIMMIX and CORR procedures (SAS). Hair type-color interacted with the time of day to affect VT; REGULAR heifers registered greater VT than SLICK and SENEPOL from 2200 to 2400 h (39.33±0.03, 38.84±0.01, and 38.74±0.02 °C, respectively). The highest positive correlations between THI and VT were obtained when using the THI value from seven hours earlier in SENEPOL (r=0.25) and SLICK (r=0.30), and from eight hours earlier in REGULAR (r=0.32) heifers. Regardless of color, the short-haired phenotype conferred superior thermoregulatory capacity. We suggest introducing genes for the slick phenotype of the Senepol into other Puerto Rican beef breeds as a means of reducing the negative impact of heat stress.