The post partum mare

Abstract

Because of the long gestation period, a mare should conceive soon after foaling in order to foal every year. Although lactation is high and uterine involution incomplete, the mare is able to conceive during the first post partum (p.p.) oestrus. Normal delivery causes little damage to the uterine epithelium. The numerous microcaruncles disappear rapidly by degeneration and resorption. A tremendous decrease in uterine size takes place after foaling, particularly during the first week after foaling. By 3 weeks p.p. the uterus has returned to the pregravid size. For several days following parturition the uterus is extremely firm upon transrectal palpation, probably because of the extensive p.p. oedema. Intrauterine fluid collections are largest 1 to 2 d p.p. and decrease gradually between days 4 and 7; no fluid is normally detected after day 16. The process of bacterial elimination is not completed in all mares during the foal heat, but the incidence of positive cultures is much lower than shortly after foaling. Neutrophils are a common finding in uterine swabs <6 d p.p., and some mares show low numbers of neutrophils still during the foal heat. The uterine environment changes markedly even after the first p.p. ovulation. After day 16, protein and enzyme levels in uterine lavage fluid of p.p. mares had decreased to normal levels, showing that the secretory function had been restored to the pregravid state. Trypsin inhibitor capacity, lysozyme levels and neutrophil numbers in uterine lavage fluid during foal heat tended to be higher in mares from which no embryos were recovered, suggesting that a persisting inflammation at the end of foal heat may be the best explanation for lowered pregnancy rates. The presence of ultrasonically detectable intrauterine fluid has also been show to decrease foal heat pregnancy rates.