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.