A high-calcium/low-phosphorus diet appears to help cows utilize dietary calcium more efficiently.
In an experiment reported in this month's Journal of Dairy Science, researchers from the Louisiana State University Ag Center compared the effects of high-calcium/low-phosphorus diets with other combinations. The researchers did not see any differences in overall health or milk production between the treatments. Yet, calcium absorption was highest when cows were fed the high-calcium/low phosphorus diet. (The high calcium/low phosphorus diet contained 0.65 percent calcium on a dry-matter basis and 0.37 percent phosphorus.)
The take-home message, according to lead researcher Vinny Moreira, is that multiparous cows can use dietary calcium and phosphorus more efficiently if dietary phosphorus is kept within NRC (2001) recommendations. Prolonged bone mobilization observed in cows fed higher levels — approximately 0.47 percent phosphorus, on a dry-matter basis — meant that those cows were wasting dietary calcium when cows in the other treatments had already decreased mobilization back to basal levels observed at calving, he says. Cows fed higher levels of phosphorus could, theoretically, have weaker bones on a temporary basis than their counterparts fed phosphorus according to NRC (2001) recommendations.