Thermoregulatory responses of ewes to winter shearing in mid- or late-pregnancy

Shearing ewes during mid or late gestation can improve lamb birth weight and vigor. The aim was to compare the thermoregulation and metabolic responses of ewes shorn in mid versus late gestation during winter. Sixty-seven Merino ewes were allocated to four experimental groups according to the stage of gestation in which they were shorn (Day 87 or Day 117) and whether ewes were shorn or not (shorn or non-shorn ewes; Sh or NSh). Rectal (RT), tympanic (TT), and maximum corneal temperature were recorded, and blood triiodothyronine and β-hydroxybutyrate concentrations were determined. Heat loss indexes were calculated using TT and MCT temperatures. RT was higher in NSh than Sh ewes (P < 0.0001). After shearing, RT remained stable in NSh ewes but decreased in Sh ewes (P < 0.001). The TT heat loss index was higher in NSh ewes (P < 0.0001), and declined post shearing in Sh ewes (P < 0.0001), indicating increased peripheral vasoconstriction. Shearing triggered acute thermogenesis as indicated by increased blood triiodothyronine and β-hydroxybutyrate concentrations in Sh than NSh ewes (P = 0.001 and P = 0.03, respectively). Shearing pregnant ewes during winter triggered significant thermoregulatory responses that were insufficient to maintain core body temperature. The responses were energetically demanding, as indicated by increased β-hydroxybutyrate and triiodothyronine concentrations.