The impact of dietary phosphorus levels on growth, slaughter, and digestive metabolism in growing sheep

Phosphorus (P) pollution from livestock farming poses significant environmental challenges, necessitating efficient P utilization. This study systematically investigated the effects of varying dietary P levels on growth, slaughter performance, nutrient digestion, and metabolism in <i>Yunnan Semi-fine Wool Sheep</i> during the growth phase. Forty-five sheep (30.33 ± 0.56 kg) were randomly assigned to five dietary P levels (0.40, 0.51, 0.68, 0.82, and 0.97%) over a 44-day trial, including a 14-day pre-feeding and 30-day formal trial period. Digestibility trials were conducted on days 22-27, and selected sheep were slaughtered for detailed analysis. Results showed no significant effects of dietary P on daily weight gain, feed-to-gain ratio, or organ indices (<i>p</i> > 0.05). However, dry matter intake, liver, and lung weights decreased linearly with increasing P levels (<i>p</i> < 0.05). Carcass traits such as left half carcass rate and net rib rate varied significantly (<i>p</i> < 0.05), showing quadratic trends. P levels also affected P, calcium, protein, and energy metabolism, as well as apparent digestibility of acid detergent fiber (<i>p</i> < 0.05). Using endogenous loss and comparative slaughter methods, the P maintenance requirement was determined as: Retained <i>p</i> = 0.5436 × Intake P - 0.0614 (<i>R</i> ² = 0.83, <i>p</i> < 0.01). P requirements for growth were modeled as: P (g/kg EBW) = 30.95772 × EBW - 0.5031. The recommended dietary P level was 0.40%, with maintenance and growth requirements of 0.06 g/EBW and 5.34-6.19 g/kg EBW, respectively, providing a foundation for P reduction strategies.