Effect Of Estrogen and Progesterone on Feed Intake and Hydroxyproline Excretion Following Induced Hypocalcemia in Dairy Cows

The effect of the {emale sex hormones, estrogen and progesterone, and feed (calcium) intake on the ability of cows to replace blood calcium after induced hypocalcemia was investigated ha two experiments.Intravenous infusion of the disodium salt of ethylenediaminetetraacetic acid (EDTA) was used to induce hypocalcemia.Percent hacrease in urinary hydroxyproline excretion was the index of bone resorption.Neither estrogen injected at parturient levels nor progesterone at mid-pregnancy levels interfered with bone resorption, as thus indicated.Estrogen reduced feed dry matter intake, and thus calcium intake, whereas progesterone partially counteracted the effect of estrogen on dry matter intake.In both experiments multiple linear regression of the drop in serum calcium (mg/100 ml) due to EDTA infiasion, on (X1) calcium intake (g Ca/100 kg body wt/day) and (Xz) percent increase ha hydroxyproline excretion accounted for a significant portion of the variation.This demonstrated that the amount of calcium mobilized during hypocaleemia was dependent both on the quantity of calcium available for absorption from the gut and bone resorption, l~atios of the standard partial regression coefficients for calcium intake divided by percent increase in hydroxyproline excretion (1.35 and .78for Experiments 1 and 2) indicated that intestinal absorption of calcium and bone resorption, as indicated by hydroxyproline excretion, were of