The influence of postnatal nutrition on reproductive tract and endometrial gland development in dairy calves.

Uterine gland development occurs after birth in cattle and other mammals. The timeline of gland development has been described in various species, but little is known about how postnatal diet influences uterine gland development. This is especially concerning in dairy heifers, where a variety of milk replacer and whole milk nutrition options exist. Little work also exists in cattle to describe how early exposure to steroids influences reproductive tract and uterine gland development. The objective of this work was to determine the effects of early postnatal plane of nutrition and estrogen supplementation on uterine gland development in calves. In both studies, Holstein heifer calves were assigned to restricted milk replacer (R-MR) or enhanced milk replacer (EH-MR) diets. In study 1, calves (R-MR, n = 6; EH-MR, n = 5) were euthanized at 8 wk. In study 2, calves were weaned at 8 wk and administered estradiol (R-MR, n = 6; EH-MR, n = 6) or placebo (R-MR, n = 6; EH-MR, n = 5) for an additional 14 d before euthanasia. Average daily gain and final body weight was greater in both studies in heifers fed the enhanced diet. At 8 wk, EH-MR calves had a greater number of glands and a smaller average gland size, but total gland area was not different from the R-MR group. At 10 wk, uterine gland number and size were not affected by diet or estrogen. Expression profiles of several paracrine mediators of gland development were examined. Increases in transcript abundance for IGF1 and IGFBP3 and a decrease in abundance of WNT7A were detected in calves fed the enhanced diet at 8 wk of age. Plane of nutrition did not affect transcript profiles at 10 wk of age, but estradiol supplementation decreased MET and WNT7A transcript abundance. To conclude, heifer calves on a restricted diet exhibited a uterine morphology and transcript profile suggestive of delayed uterine gland development. These changes appear to be corrected by wk 10 of life. Also, this work provides evidence supporting the contention that early estradiol exposure has detrimental effects on uterine gene expression.