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

Abstract

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 induring the growth phase. Forty-five sheep (30.33&#x202f;&#xb1;&#x202f;0.56&#x202f;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 (&#x202f;>&#x202f;0.05). However, dry matter intake, liver, and lung weights decreased linearly with increasing P levels (&#x202f;<&#x202f;0.05). Carcass traits such as left half carcass rate and net rib rate varied significantly (&#x202f;<&#x202f;0.05), showing quadratic trends. P levels also affected P, calcium, protein, and energy metabolism, as well as apparent digestibility of acid detergent fiber (&#x202f;<&#x202f;0.05). Using endogenous loss and comparative slaughter methods, the P maintenance requirement was determined as: Retained&#x202f;=&#x202f;0.5436&#x202f;&#xd7;&#x202f;Intake P - 0.0614 (&#x202f;=&#x202f;0.83,&#x202f;<&#x202f;0.01). P requirements for growth were modeled as: P (g/kg EBW)&#x202f;=&#x202f;30.95772&#x202f;&#xd7;&#x202f;EBW - 0.5031. The recommended dietary P level was 0.40%, with maintenance and growth requirements of 0.06&#x202f;g/EBW and 5.34-6.19&#x202f;g/kg EBW, respectively, providing a foundation for P reduction strategies.