Heat stress response in slick vs normal-haired Criollo Limonero heifers in a tropical environment

To assess the effect of hair type on the heat stress response, 20 Criollo Limonero heifers with slick ( n = 11) or normal hair ( n = 9) were studied. Under a high temperature-humidity index (THI) environment, heat stress response was assessed through physiological variables that included respiration rate (RR), heart rate (HR), ruminal frequency (RMF), rectal temperature (RT), saliva pH (SPH), and lymphocyte count (LC) in the morning (5:00 AM, 27.4 °C, 64% relative humidity, THI = 77) and afternoon (1:00 PM, 34.5 °C, 70% relative humidity, THI = 88). A case–control study using a split plot design was used. Data were analyzed using ANOVA (PROC MIXED SAS 2010 ) and a statistical model comprising the fixed effects of hair length, sampling hour, interaction of hair length by sampling hour, and the random effect of animal nested within hair type on physiological variables associated with heat stress response. Sampling hour influenced ( P