Effects of dietary crude proteins on constituents of plasma and uterine secretions were examined at various stages of the estrous cycle of high producing Holstein cows. Eighteen cows were assigned randomly to isocaloric diets (74% total digestible nutrients) containing either 12 or 23% crude protein (dry matter) on day 40 postpartum. Uterine secretion and coccygeal blood samples were collected at estrus, days 5 and 15 of the first estrous cycle after day 50 postpartum, and at the subsequent estrus. The 23% crude protein diet resulted in higher concentrations of ammonia in blood, urea in blood plasma and uterine secretion, and phosphorus and potassium in plasma. Zinc increased during the estrous cycle in plasma of cows fed 23% crude protein and decreased in cows fed 12% crude protein. Magnesium concentrations in uterine secretions were lower in cows on 23% crude protein. Potassium and phosphorus also were lower in uterine secretions of cows fed 23% crude protein but only during the luteal phase of the estrous cycle. Zinc concentrations in uterine secretions decreased faster during the estrous cycle in cows fed 12% crude protein than in cows fed 23% crude protein. Thus, the crude protein content of the diet altered concentrations in blood of ammonia and concentrations in plasma of urea, phosphorus, potassium, and zinc. Crude protein content of the diet altered concentrations in uterine secretion of urea, magnesium, potassium, phosphorus, and zinc.

No abstract

No abstract

No abstract

Summary Major progress on the endocrinology of the pregnant mare has been possible thanks to the catheterised equine fetal preparation developed by Marian Silver. In particular, these preparations led to the identification of the source of progestagens within the feto‐placental unit and provided the impetus for further work on their biosynthesis and biological activities. The biosynthesis of the progestagens involves close interaction between the fetus, the endometrium and the placenta, and gives rise to some fundamental biochemical questions. The biological role of the progestagens is also discussed: these compounds may have progestagenic activities but may also play a role in the onset of parturition.