Premature regression of the corpora lutea in superovulated cows

Morphological and functional regression of the CL was shown by $\text{15}\text{55}$ (27%) superovulated dairy cows at slaughter on D 14. Neither the routine injection of a PMSG-antiserum at the induced superovulatory oestrus, nor intrauterine infections proved to be responsible. Animals with regressed CL however had significantly lower progesterone levels in the peripheral blood at the time PMSG (D 10, P = 0,05) and prostaglandin (D 12, P = 0,02) were injected, as compared to superovulated animals with normal CL. At the induced superovulatory heat, the differences between the 2 groups disappeared. From D 4 after superovulation the differences in progesterone concentration between the 2 groups became significant again (P = 0,02 – 0,05). It is not yet clear whether the observed luteal dysfunction is due to an inadequate luteotrophic stimulus or to a premature luteolysis. The luteal regression could be caused either by a genuine luteal insufficiency of the midcyle CL or by poor heat detection.