Influence of dietary protein levels on metabolism of nitrogen, phosphorus, and calcium in a Chinese indigenous sheep (Ovis aries).

Protein balance in ruminants' dietary regimens is crucial since it influences not just the production, fertility, and health of these animals, but also reduces worldwide environmental concerns regarding methane emissions. The current experiment explored the influence of dietary protein levels on nitrogen, calcium, and phosphorus metabolism and their environmental excretion using the Yunnan semi-fine wool sheep (YSFW) as the animal model. For this, 25 YSFW sheep (male, 10-month-old, averaging live body weight 38.5 ± 1.5 kg) were randomly divided into five groups (n = 5 rams/group) using a completely randomized design. The groups were assigned to one of five dietary treatments with protein concentrations of 8.3, 10.4, 12.4, 14.9, and 19.2% on a dry matter basis. The study period included a 14-day dietary adaptation, 30-day feeding, and 15-day digestibility tests. The intakes of nitrogen and phosphorus were increased (P < 0.05) with the increasing dietary protein levels. Similarly, nitrogen digestibility was improved (P < 0.05) by feeding a higher level of dietary protein. The fecal phosphorus and urinary nitrogen contents were higher (P < 0.05) for the 19.2% dietary protein-fed group than those fed on the rest protein levels. The calcium contents in urine were greater (P < 0.05) in the 8.3% dietary protein-fed group than in other groups. However, urinary phosphorus excretion was the highest (P < 0.05) for the 14.9% dietary protein-fed sheep across the treatments. The total excretion (feces plus urine) of nitrogen and phosphorus contents was increased (P < 0.05) by feeding the higher protein-containing diets. The deposition of nitrogen, calcium, and phosphorus was improved (P < 0.05) by feeding higher dietary protein levels. According to these findings, feeding dietary protein levels ranging from 8.3 to 10.4% can enhance nitrogen deposition rates in sheep by increasing nitrogen and phosphorus utilization efficiency, and thus, reducing environmental pollution.