Higher cortisol and testosterone levels in sheep with larger litter sizes

Maternal resources mediate fetal growth and development. This study analyzes the association between maternal cortisol and testosterone levels in late pregnancy and litter size in sheep. Concentrations of cortisol and testosterone in the plasma and wool were determined by enzyme-linked immunosorbent assay (ELISA) kits in Afec-Assaf ewes with one to four fetuses. Concentrations of cortisol in the plasma at 130 days of gestation, and in wool grown in the last 2 months of gestation were greater (P < 0.05) in ewes lambing two or more lambs, compared to ewes producing a single lamb. Whereas there was no association between litter size and plasma concentration of testosterone at 130 days of gestation (P > 0.05), testosterone concentration in the wool was significantly associated with litter size (P < 0.05). We suggest that elevated cortisol and testosterone levels in ewes with multiple fetuses may serve as a mechanism to lower fetal weight, thereby decreasing fetus-related metabolic load in prolific sheep.