Plasma thyroid hormones concentrations in donkey stallions (Equus caballus)

Thyroid function was studied in normal libido (reaction time <5 min; n=6) a nd low libido donkey stallions (reaction time >30 min; n=6) at 15 days inte rval during breeding (July and August) and nonbreeding seasons (December an d January). Significantly (P<0.01) elevated profiles of plasma T-3 and T-4 were recorded in normal libido stallions compared to low libido donkey stal lions during breeding and nonbreeding seasons. Thyroid hormones registered significant (P<0.01) decrease during nonbreeding season in both normal and low libido donkey stallions. However, variations in thyroid activity were n onsignificant between months during breeding and nonbreeding seasons in the 2 groups of stallions.