Influence of long-term feeding of limited amounts of phosphorus on dry matter intake, milk production, and body weight of dairy cows

For almost two lactations, 24 high-yielding, multiparous dairy cows were fed a basal diet and concentrate mixtures with three different P concentrations. The basal diet consisted of grass (silage or artificially dried), corn silage, wet beet pulp, straw, and concentrates. The concentrate mixtures differed only in P content by varying the amount of monosodium phosphate. The number of cows and the amount of dietary P, expressed as a percentage of current recommendations in the Netherlands were: 6 cows, 100% (P100); 9 cows, 80% (P80); and 9 cows, 67% (P67). This resulted in dietary P concentrations of 3.3, 2.8, and 2.4 g/kg of dietary DM for the P100, P80, and P67 treatments, respectively. The trial lasted for 21 mo, including two lactations and two dry periods. Feed intake of the P67 group was reduced significantly during the first dry period. Dry matter intake, milk yield, and body weight were all reduced with the low P treatment during the second lactation. Phosphorus had no effect on reproductive performance. Between P100 and P80, no effect on any of the variables in this trial was observed. Results suggests that the diet with 2.8 g of P/kg of dietary DM proved to be sufficient to meet the P requirement of dairy cows producing approximately 9000 kg of milk per lactation.