Effects of diet crude protein level on the production performance, nutrient digestion, and serum parameters of finishing Hu sheep

The objective of the present study was to evaluate the effects of diet crude protein level on the production performance, nutrient digestion, and serum parameters of finishing Hu sheep. A total of 54, four-month-old male Hu sheep (32.25 ± 2.5 kg) were randomly divided into three treatments, with sheep in each treatment being of similar ages and weights, and each treatment containing 18 sheep. The three dietary crude protein (CP) levels used were 11.5%, 14.0%, and 16.5%. The pre-test period was seven days, while the formal test period was 63 days. The results showed that: 1) The average final body weight of Hu sheep was significantly lower in the 11.5% CP group than in the 14.0% and 16.5% CP groups (P < 0.05), and the feed efficiency of the 11.5% CP group was significantly higher than the 16.5% CP group (P < 0.05). Furthermore, there were no significant differences in dry matter intake among groups (P > 0.05), and average daily gain tended to be greater (0.05 < P < 0.1) in the 14.0% and 16.5% CP groups compared to the 11.5% CP group. 2) Dry matter, organic matter, neutral detergent fiber, and acid detergent fiber contents were all significantly higher in the 16.5% CP group than in the 11.5% CP group (P < 0.05). 3) Nitrogen intake was significantly higher in the 14.0% and 16.5% CP groups than in the 11.5% CP group. There were significant differences in urine nitrogen emissions among groups (P < 0.05) and the apparent digestibility of nitrogen was significantly higher in the 16.5% CP group than in the 11.5% and 14.0% CP groups (P < 0.05). 4) The serum albumin, albumin/globulin ratio of the 16.5% CP group was significantly lower than the 11.5% and 14.0% CP groups (P < 0.05), but globulin content was significantly higher than in the other groups (P < 0.05). The alanine aminotransferase content was significantly higher in the 11.5% CP group than in the other groups (P < 0.05). Triglyceride and total cholesterol were significantly lower in the 16.5% CP group than in the 11.5% CP group (P < 0.05). Serum urea nitrogen content differed significantly among groups (P < 0.05), but there were no significant differences in other serum indicators. In summary, the 14.0% and 16.5% CP groups significantly increased fattening effects in the Hu sheep but reduced the nitrogen use efficiency.