Acute thermoregulatory responses of ewes to winter shearing at mid-gestation

Abstract

Winter shearing is commonly performed on pregnant wool ewes raised in pastoral systems, as it enhances lamb birth weight and survival. However, little is known about ewes' thermoregulatory responses. The aim of this study was to determine the acute thermoregulatory responses of pregnant ewes subjected to winter shearing. The experiment was conducted at the Campo Experimental Nº 1, Facultad de Veterinaria, Udelar, Canelones, Uruguay, with 23 multiparous Merino ewes (3 to 4 years). On day 67 of gestation, ewes were randomly assigned to two groups homogeneous in body weight and body condition score (BCS) (47.8 ± 5.5 kg and a BCS between 2.5 and 3.5 on a scale of 1 to 5). The day after, 11 ewes were sheared (Sh group), and 12 remained unshorn (Con group). Shearing was performed using the Tally-Hi procedure, starting at 2:00 PM, and lasted approximately 5 minutes per animal. The following day, between 9:00 and 11:00, rectal and tympanic temperatures were measured with thermometers, and a heat loss index (HLI) was calculated [HLI = (surface temperature-environmental temperature)/(RT-environmental temperature)]. Additionally, β-hydroxybutyrate levels were determined using a portable analyzer. The groups were compared using the Mann-Whitney test (for non-normal data) or Student's t-test (for normal data). Rectal temperature was lower (38.18±0.16ºC vs 39.1±0.07ºC; P<0.01) and the HLI tended to be approximately 3.16% greater (0.95±0.01 vs 0.92±0.003; P=0.058) in Sh than Con ewes. No differences were observed in tympanic temperature or circulating β-hydroxybutyrate levels. In conclusion, winter shearing elicited thermoregulatory responses and underscored the ability of pregnant ewes to modulate these responses during mid-gestation, including a strong decrease in the central temperature that the acute vasoconstriction could not compensate. This result contributes to a better understanding of the impact of this practice on the physiology and welfare of pregnant ewes.