Some Practical Considerations for Improving the Pregnancy Rate of Tropical Merinos

The strategic use of natural shade and iodine supplementation at the time of joining led to an improved fertility of tropical Merino ewes. This was most pronounced when ambient heat stress was greatest (p <O.Ol). A higher incidence of oestrus and a higher pregnancy rate in mated animals both contributed to the improved fertility. Heat' stress conditions experienced during summer in a tropical semi-arid environment were sufficient to cause a suppression of oestrous activity. Temporary relief from these conditions brought about by a cool change and an associated storm led to a marked synchronization of oestrus. The aberrent oestrus cycle-lengths of "synchronized" ewes were not specifically associated with a reduction in pregnancy rate.