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Effect Of Estrogen and Progesterone on Feed Intake and Hydroxyproline Excretion Following Induced Hypocalcemia in Dairy Cows¹

Department of Dairy Science, Ohio Agricultural Research and Development Center, Wooster 44691

ABSTRACT

The effect of the female sex hormones, estrogen and progesterone, and feed (calcium) intake on the ability of cows to replace blood calcium after induced hypocalcemia was investigated in two experiments. Intravenous infusion of the di-sodium salt of ethylenediaminetetraacetic acid (EDTA) was used to induce hypocalcemia. Percent increase 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 infusion, on (X₁) calcium intake (g Ca/100 kg body wt/day) and (X₂) percent increase in hydroxyproline excretion accounted for a significant portion of the variation. This demonstrated that the amount of calcium mobilized during hypocalcemia was dependent both on the quantity of calcium available for absorption from the gut and bone resorption. Ratios of the standard partial regression coefficients for calcium intake divided by percent increase in hydroxyproline excretion (1.35 and .78 for Experiments 1 and 2) indicated that intestinal absorption of calcium and bone resorption, as indicated by hydroxyproline excretion, were of about equal importance in preventing the decline in serum calcium induced by EDTA infusion.

These results indicate that the major involvement of high blood estrogen at parturition in parturient paresis is not through inhibition of bone resorption but rather through decreased absorption of intestinal calcium caused by estrogen induced inappetence.

¹ Journal Article 104-71, Ohio Agricultural Research and Development Center, Wooster 44691.

² Present Address: Merck & Co., Inc., Rahway, New Jersey.

³ Data in this paper were presented to the Graduate Faculty of The Ohio State University in partial fulfillment of the requirements for the degree Doctor of Philosophy.