Prolonged Gestation

History. You are called to examine a purebred Holstein cow that is 12 days overdue compared with the herd gestation average of 280 days. She was artificially inseminated, was diagnosed pregnant 35 days later, and has not been observed in estrus since insemination.

Clinical Examination. The cow has a greatly enlarged abdomen. On palpation of the uterus per rectum, you find the presence of a large calf. The cow certainly appears to be term as far as the size of the calf. You are puzzled, however, by the lack of colostrum in the udder.

Comment. The history and physical examination findings are compatible with an animal that has a fetus that is defective in terms of the initiation of parturition. A normal fetal hypothalamic-pituitary-adrenocortical system is essential for the production of cortisol, which initiates the delivery process. In the cow, this can begin 3 to 4 weeks prepartum, with fetal cortisol directing the increased production of estrogen; this in turn eventually initiates PGF_2n synthesis and release. The deficit could be caused by a malformed adrenal gland, pitui­tary, or hypothalamus. In one syndrome described for Holsteins, the critical defect was a lack of corticotropin-pro­ducing cells in the pituitary, which led to inadequate stim­ulation of the adrenal cortex and inadequate fetal cortisol production. The lack of lactogenesis reflects that the endo­crine changes beginning 3 to 4 weeks prepartum as a prelude to delivery are also important for lactogenesis, and in their absence, Colostral formation is delayed.

Treatment. The animal can respond to glucocorticoids, with delivery usually occurring 2 to 3 days later. The placenta is normal in this situation, and the systemic administration of glucocorticoids substitutes for fetal cortisol in initiating the endocrine events that lead to parturition. Lactogenesis is usually initiated by glucocorticoid treatment, although the process is usually less advanced than that expected at normal delivery. Because the calf continues to grow in utero in this syndrome, it is often too large to be delivered per vαginαm, and a cesarean section may have to be performed 2 to 3 days after treatment in concert with dilation of the cervix.

You need to tell the owner that the calf will likely not survive because of inadequate adrenal secretion. If the calf were an extremely valuable bull prospect, one could admin­ister both glucocorticoids and mineralocorticoids for a num­ber of months with the hope the animal would eventually be able to take over its own adrenal support (this actually occurred in one case at the University of California-Davis). It would be questionable, however, to initiate treatment of the calf on the basis that the disease is an autosomal recessive inherited condition.