Effects of Ten Types of Diets on Nitrogen Balance and Excretion of Purine Derivatives in Hu Sheep

This experiment aimed to investigate the effects of ten concentrate feedstuffs on nitrogen balance and urinary purine derivative (PD) excretion in Hu sheep. Fifteen healthy 5-month-old Hu sheep (average body weight:25.31±2.24 kg) were randomly divided into 3 groups (5 sheep per group). The experiment consisted of 4 phases, with 3 treatments per phase and 5 replicates per treatment. A single-factor design was adopted, and the experimental diets comprised 10 total mixed rations (TMR). Each diet was fed for 20 days, including a 15-day adaptation period followed by a 5-day formal trial period, during which total feces and urine were collected and stored at −20°C. Results showed that nitrogen intake and total nitrogen excretion in sheep fed soybean meal, rapeseed meal, walnut meal, flaxseed meal, cottonseed meal, and rice distillers’ grains diets were significantly higher than those fed oat-,wheat-, corn-, and wheat bran-based diets ( P <0.05). Urinary nitrogen excretion in the walnut meal and soybean meal groups was significantly higher than in the other eight diets ( P <0.05). Absorbed nitrogen and nitrogen retention in the soybean meal and rapeseed meal groups were significantly higher than in the other eight diets ( P <0.05). Urinary uric acid excretion ranged from 0.14 to 0.40 mmol/d,with allantoin accounting for 85.63%–89.26% of total PD excretion. The proportion of uric acid in total PD excretion (0.81%–2.14%) was significantly lower in the rapeseed meal diet than in the other nine diets ( P < 0.05). Xanthine and hypoxanthine collectively represented 9.73%–12.92% of total PD excretion. The purine nitrogen index (PNI) of the four energy-supplemented diets was significantly higher than that of the five protein-supplemented diets (excluding rice distillers’ grains) ( P <0.05). These findings indicate that dietary composition and concentrate type significantly influence nitrogen excretion patterns in Hu sheep. Under the experimental conditions,sheep fed low-protein diets excreted nitrogen via both fecal and urinary pathways,whereas high-protein diets shifted nitrogen excretion predominantly to urine,with urinary nitrogen surpassing fecal nitrogen. Urinary PD excretion increased proportionally with elevated dietary nitrogen levels. This study provides critical insights into optimizing feed formulations to enhance nitrogen utilization efficiency and mitigate environmental pollution in ruminant production systems.