Long-term effects of feeding diets without mineral phosphorus supplementation on the performance and phosphorus excretion in high-yielding dairy cows

Abstract

The objective of this study was to assess the long-term effects of feeding a diet with no mineral phosphorus (P) supplementation on performance and P excretion in high-yielding dairy cows. In exp. 1, 24 primiparous (PP) and 40 multiparous (MP) Holstein cows were allocated to one of two treatments at calving: (1) regular corn silage and alfalfa haylage based milking cow total mixed ration (TMR; 0.42% P diet) or (2) milking cow total mixed ration (TMR) without supplemental mineral P (0.35% P diet) in a completely randomized design. The trial lasted until after two lactations were completed or the cow was culled. In exp. 2, eight MP Holstein cows (108 ± 8.0 d in milk) were used to determine P digestibility and retention in a completely randomized block design. In exp. 1, the 0.35% P diet cows had lower body weight, body condition score and milk urea nitrogen and higher faecal P than the 0.42% P cows. The dry matter intake (DMI) of PP cows on the 0.35% P diet was lower than that of PP cows on the 0.42% P diet. There was no difference in the DMI of MP cows. The P intake of 0.35% P diet PP cows was 30% lower than that of 0.42% P diet PP cows. The P intake of 0.35% P diet MP cows was 20% lower than that of 0.42% P diet MP. The digestibility coefficient of P for the 0.35% P diet was higher than that for the 0.42% P diet. These results suggest that the forages used in the present study contained adequate amounts of P to sustain milk production in high-yielding MP cows. However, for PP cows some mineral P supplementation is recommended especially during early lactation. Key words: Phosphorus, environmental pollution, intensive dairy operations