Endocrine and metabolic responses to winter shearing in pregnant and non-pregnant Merino ewes

Winter shearing may challenge ewe thermal balance, particularly during gestation when metabolic demands increase. This study evaluated the main and interactive effects of pregnancy and winter shearing on endocrine and metabolic responses in Merino ewes using a factorial design (pregnancy × shearing). Thirty ewes (14 pregnant -single bearing, 16 non-pregnant) were allocated to dry unshorn, dry shorn, pregnant unshorn, and pregnant shorn groups. Shearing was performed on day 103 post-timed artificial insemination. Blood was sampled from day -3 to 15 relative to shearing to measure concentrations of triiodothyronine (T3), thyroxine (T4), cortisol, insulin, insulin-like growth factor 1 (IGF-1), glucose, non-esterified fatty acids (NEFA), and beta-hydroxybutyrate (BHB). Body weight (BW) and body condition score (BCS) were recorded, and meteorological data were used to calculate the chill index. Pregnancy affected T3, IGF-1, glucose, NEFA, and BHB (P < 0.05), whereas shearing had no significant effects (P > 0.05). Pregnant ewes showed lower T3 and glucose and higher IGF-1, NEFA, and BHB (P < 0.05). A tendency for a pregnancy × shearing interaction was observed for glucose (P = 0.065). All variables changed over time (P < 0.05). Periods of higher Chill Index coincided with increases in T3 and T4 and decreases in NEFA. Body weight and BCS were unaffected (P > 0.05). In conclusion, pregnancy was the primary driver of endocrine and metabolic responses during the 15-day post-shearing period, whereas winter shearing did not induce sustained endocrine or metabolic alterations under the environmental conditions of the present study.