THE EFFECTS OF CALCIUM CARBONATE ON THE APPARENT DIGESTIBILITY, SERUM CONCENTRATION AND APPARENT RETENTION OF DIETARY MINERALS IN DAIRY CATTLE

Abstract

CaCO3 was added to a hay-grain ration already adequate in nutrients to determine the effect of doubling the Ca content of the ration on apparent digestibilities and serum levels of 11 minerals. Sixteen dairy cattle of two breeds (Holstein and Ayrshire) were randomly assigned to the control (0.7% Ca) or Ca-treatment (1.5% Ca) based on calving order. Each animal was fed to appetite for 80 days postpartum with no difference (P > 0.05) occurring between treatments in intake when expressed as a percentage of body weight. Five animals from each treatment were exposed to a 5-day digestibility trial. No change in organic matter apparent digestibility occurred but there were higher (P < 0.05) levels of Ca and Fe, increased (P < 0.01) levels of Cu, and lower (P < 0.05) Zn and Mo apparent digestibilities for animals on the Ca-treatment. Fecal pH was higher (P < 0.05) in the Ca-treated cows indicating a buffering action of the added CaCO3. In the serum, Ca and Zn concentrations were higher (P < 0.01), Cu increased (P < 0.05), and P was lower (P < 0.01) than the levels for the control animals. Breed effects were discernible as both P and Cu were higher (P < 0.01) in the serum of Ayrshires than of Holsteins. No change (P < 0.05) was evident in the secretion of minerals into the milk but urinary P concentration was higher (P < 0.05) in the control group. CaCO3 supplementation of the diet allowed the animals to go from a negative to a positive Ca balance (P < 0.01) and increased (P < 0.05) the amount of P apparent retention. In all, six essential minerals had altered apparent digestibilities and/or serum concentrations with possible long-term effects on animal metabolism. Key words: Calcium, mineral balance, digestibility, serum, dairy cattle