Effects of High Grain Diets on Calcium Metabolism in Sheep

Abstract

The effect of dietary contents of grain on calcium (Ca) metabolism was evaluated in adult sheep. They were fed 60 to 90% grain diets with increasing ground barley at the level of 10% every 5 days period, then a 100% hay diet was fed for eight days. Blood pH values tended to be decreased and urinary net acid excretion (NAE) was gradually increased as higher grain diets were offered. Although plasma total Ca concentrations were linearly decreased and urinary Ca excretion was increased with the elevation of dietary grain contents, plasma ionized Ca concentrations were little decreased in sheep fed the high grain diets. A decrease in fractional renal tubule reabsorption rates of Ca was responsible for the increase in urinary Ca excretion in part. Circulating immunoreactive parathyroid hormone (iPTH) levels were elevated in sheep fed the high grain diets, while plasma ionized Ca concentrations were little changed. There was no significant relationship between plasma ionized Ca concentrations and NAE (r=-0.18, p>0.23), but a. significant correlation between plasma total Ca concentrations and NAE (r=-0.56, p<0.001). Also, there was a positive correlation between plasma iPTH levels and NAE (r=0.40, p<0.01).