Individual differences in the phosphorus metabolism of fattening bulls--testing effects of crude fibre and calcium chloride in the diet.

Urolithiasis due to struvite concrements occurs in fattening cattle, but only in 1-5% of a herd, in spite of identical nutrient supply. Developing dietetic measures for these cattle was the primary aim of this study. The feeding experiments were focused on the general effects of varying the crude fibre supply and adding CaCl2 as a urine acidifier, especially concerning individual reactions to the different diets. Five standard balance trials were performed with three fattening bulls. The crude fibre content in the ration varied between 14.8% and 24.0% DM. In two trials, coated CaCl2 was fed (per day 20 g/100 kg BW). Influences on the macro mineral metabolism and the acid-base-balance were investigated. Unexpectedly, the crude fibre content had no significant effect on the renal P excretion, but individual differences occurred concerning digestibility, renal excretion and serum concentration of P: one bull constantly showed significantly higher values. Adding CaCl2 resulted in reduced renal P excretion and pH values of the urine (< 6.5). Thus, using CaCl2 might be a beneficial dietetic measure for preventing struvite. The huge individual differences in the P metabolism could be linked to genetically-based variations, as known for sheep.