Effect of shade use during gestation and lactation: thermoregulatory responses of ewes and lambs

Abstract

Exposure to sunlight during gestation and lactation may cause heat stress in ewes and their lambs, compromising their thermoregulatory efficiency. This study evaluated the effects of the presence or absence of shade on the physiological responses of these animals. The experiment occurred at the FAZU teaching farm in Uberaba, MG, Brazil. Twenty-three ewes in their final third of gestation (55 ± 5 kg, 36 ± 6 months old, body condition score 3-3.5) were randomly assigned to two treatments: SET (paddocks without shade; N=11) and SAT (paddocks with 70% shade cloth; N=12). At birth, 31 lambs (15 males and 16 females; SET: 7 M and 9 F; SAT: 8 M and 7 F) were identified and kept with their mothers. Respiratory rate (RR; movements min⁻¹), rectal temperature (RT; °C), auricular temperature (AT; °C), and sweating rate (SR; g m⁻² h⁻¹) were measured for each participant. In ewes, seven weekly samplings were conducted from 30 d before lambing until the end of lactation, and in lambs, two samplings were performed between 30 d of age and weaning. Collections were performed weekly during periods of the greatest temperature variation (08:00 AM, 11:00 AM, 02:00 PM, and 05:00 PM). Data were analyzed using a completely randomized design and subjected to the Shapiro–Wilk test for normality. Parametric variables were evaluated by ANOVA using the GLM procedure and Tukey’s multiple comparison test (5% significance level), considering the effects of treatment, time, and their interactions using RStudio software. The animals in the SET group showed higher RR, RT, AT, and SR values (P < 0.05) than those in the SAT group, indicating lower thermoregulatory efficiency under direct sun exposure. These results reinforce that the use of shading is an effective strategy for reducing heat stress in pregnant and lactating ewes and their lambs in tropical systems.