Anovulation, Delayed Ovulation and Luteal Insufficiency

Ovulation in the cow occurs 10 to 12 hours after the end of behavioral estrus and 18 to 26 hours after the ovulatory LH peak. During estrus and after the endof estrus, several follicles undergo development but usually only one, it ovulates & the other follicles regress and become atretic. The consequences for fertility of an ovulatory defect are two-fold; either the oocyte is not liberated and hence cannot be fertilized, or it is liberated too late so that the spermatozoa are now incapable of fertilization, or the oocyte has aged and is not capable of normal development. Ovulatory defects occur due to endocrine deficiency or imbalance, failure of the development of hormone receptors at the target tissue or mechanical factors. If the quantity of pituitary hormone released is insufficient, or its timing is incorrect, then ovulation is delayed or fails to occur. In a minority of cases, because of extensive lesions involving adhesion of the ovarian bursa to the surface of the ovary, the physical process of ovulation is prevented.