Effect of hCG on experimental luteal hypoplasia in cows.
An early ovulation was induced in 4 adult cows of the luteal stage by ad-ministration of gonadotrophin releasing hormone analogue 16 hr (group I of two cows) or 32 hr (group II of two cows) after the treatment with a prostaglandin F2α analogue. Five hundreds were administered to them daily for 10 consecutive days from the day of induced ovulation. One cow of group I luteinization was functionally insufficient and estrus appeared 5 days after induced ovulation. A small corpus luteum was formed in the other cows of this group. Luteinization was inadequate in the two cows of group II. The blood plasma progesterone level exhibited a transitional increase in the cow with a small corpus luteum formed of group I six days after induced ovulation. It remained low in the other cows of both groups even after induced ovulation. In con-clusion, treatment with hCG had no luteotrophic effect. It was presumed that luteal hypoplasia have been caused by the poor response of a follicle to luteinizing hormone after ovulation.