Mineral accretion in the fetus and adnexa during late gestation in Holstein cows

Multiparous Holstein cows (n = 18) were bred artificially to the same Holstein bull and then slaughtered at times ranging from 190 to 270 postmating to assess mineral accretion by the conceptus. Fresh weight, DM, and concentrations of Ca, P, Mg, K, Na, Fe, Zn, Cu, and Mn were obtained for the fetus, fetal fluids, fetal membranes, cotyledons, caruncles, and uterine tissues. Rates of accumulation of individual minerals in different components of the conceptus during late gestation were described by either linear or exponential relationships. Estimated Ca accretion rate in the conceptus increased from 2.3 g/d at 190 d of gestation to 10.3 g/d at 280 d of pregnancy; corresponding P accretions were 1.9 and 5.4 g/d. Rates of accretion of Mg, K, and Na in the conceptus in late pregnancy were about .2, 1.0, and 1.4 g/d, respectively, and Fe, Zn, Cu, and Mn accumulated in the conceptus at rates of 18.0, 11.7, 1.6, and .3 mg/d, respectively. These daily rates represent net mineral requirements for conceptus growth during late pregnancy in mature Holstein cows. In general, our values are consistent with current dietary recommendations for minerals during the dry period.