Long-Term Calcium-Phosphorus Studies in Confined Dairy Cows

Abstract

Calcium balance can be kept near even or positive in early lactation if calcium and phosphorus intakes and vitamin D consumption are adequate. Adequate calcium consumption promotes more rapid uterine involution and earlier ovulation. Phosphorus consumption must be adequate from day to day. There is no phosphorus-sensitive mechanism to elicit phosphorus resorption from bone. That mechanism is only calcium-sensitive. Inadequate phosphorus intake depresses appetite as well as preventing bone accretion. Phosphorus balance, with adequate phosphorus intake, largely depends on calcium adequacy since the calcium-tophosphorus ratio in bone is constant.

Our study comparing monosodium phosphate with calcium phosphate as supplements for an alfalfa hay and sorghum grain ration may have shown a chlorine deficiency. Salt was omitted from the grain but was available ad libitum. Very little salt consumption was the unique characteristic associated with the sodium phosphate treatment. Elevated chine, slab-sidedness, and tucking up in the flank were noted in the cows which ate little salt. Salt appetite appears to be sodium-sensitive.