Effects of Calcium to Phosphorus Ratio in the Diet of Dairy Cows on Incidence of Parturient Paresis

Nineteen Jersey and three Ayrshire cows (26 parturitions, second lactation and beyond) were allotted to two groups according to lactation number, milk production, and previous incidence of parturient paresis. Twelve cows were fed (for periods up to 12 mo before parturition) a complete feed of corn silage and concentrate with a calcium-to-phosphorus ratio of 1.1:1. The other cows were fed similarly except that calcium carbonate was added to increase the calcium-to-phosphorus ratio to 2.3:1. In 7 of the 14 parturitions of cows fed the 1.1:1 diet and in 9 of the 12 fed the 2.3:1 diet, treatment for parturient paresis was required. The length of time the diets were fed before parturition had no obvious effect on incidence of parturient paresis. Plasma calcium and inorganic phosphorus were lower from 48h prepartum to 48h postpartum in paretic than in nonparetic cows. Nonparetic cows fed the 2.3:1 diet had a higher plasma calcium concentration from 48h to 4 wk postpartum than did nonparetic cows fed the 1.1:1 diet. There were no other significant dietary effects on plasma calcium, magnesium, or phosphorus.