STATISTICAL RESEARCH ON FATE OF DIETARY MINERAL ELEMENTS IN DRY AND LACTATING COWS .3. PHOSPHORUS

Statistical analyses were carried out on the data obtained under very strict conditions in metabolism stalls with 41 different rations fed to 127 adult non-pregnant dry cows and with 14 other different rations fed to 35 adult non-pregnant lactating cows that had calved 2-6 months earlier and whose daily milk production ranged from 11 to 20 kg. The correlations between faecal and urinary phosphorus losses, phosphorus in milk, digestible phosphorus and phosphorus balance and the other nutritive factors of the 55 above-mentioned experimental diets have been calculated. In dry and lactating cows, with very variable intakes of phosphorus, phosphorus faecal and urinary losses show very wide variations and may be important. They are not influenced by phosphorus intake, and are related, among the many other nutritional factors we analysed only to ingested water and to a lesser extent to the nitrogen of the diet. The phosphorus balance is thus also very much variable and not really related to the composition of the ration. This low influence of the diet on the apparent fate of phosphorus can be explained by the interference of unpredictable but certainly quite variable endogenous phosphorus excretion, which is also probably responsible for the effect we found of individual factors and of the previous nutritional status. In the lactating cows, the phosphorus requirements for milk production influence the utilization of phosphorus since a significant correlation exists between phosphorus secreted in the milk and urinary phosphorus. In our experimental conditions, the Ca: P ratio does not seem to influence the fate of dietary calcium and phosphorus. © 1969, Cambridge University Press. All rights reserved.