Effects of Dietary Rumen-Undegradable Protein and Protein Levels on Growth Performance, Fermentation Parameters, Slaughter Performance, and Meat Quality on Fattening Hu Sheep

Optimizing protein nutrition in ruminants is vital for enhancing growth performance, meat quality, and overall production efficiency. However, the precise protein requirement for ruminants remains unclear. Two experimental trials were conducted to investigate the impact of varying levels of rumen-undegradable protein (RUP) on in situ feed degradability, growth performance, meat quality, and rumen fermentation parameters in fattening Hu sheep. In EXP 1, six Hu sheep were fitted with rumen fistulas to measure rumen degradation characteristics of diets varying levels of crude protein (CP) (13%, 14%, 15%, and 16% X RUP: CP 40%, 45%, 50%). The results showed that the ruminal DM and GE degradation had no difference between the experimental diets (p > 0.05). However, the CP degradation rate gradually decreased as the dietary RUP proportion increased (p < 0.05). In EXP 2, a double factorial experiment was conducted using 720 male Hu sheep, divided into twelve dietary treatments with varying levels of crude protein (CP) (13%, 14%, 15%, and 16%) and RUP (40%, 45%, and 50%). Key performance indicators such as body weight gain (BWG), average daily gain (ADG), average daily feed intake (ADFI), and feed conversion ratio (FCR) were measured at the beginning and end of the trial. Post-slaughter, meat quality attributes, including drip loss and initial pH of the longissimus dorsi muscle, were assessed after 40 days of the trial. Rumen fluid samples were analyzed for volatile fatty acid (VFA) profiles to evaluate rumen fermentation efficiency. The results demonstrated that increasing RUP levels significantly improved BWG and ADG (p < 0.05) without affecting ADFI and FCR. Although dietary protein levels had minimal impact, higher RUP levels were associated with a trend toward increased final body weight (p = 0.09). Dietary protein levels and the RUP: CP ratio had no significant effect on meat quality (p > 0.05). Ruminal acetate, valerate, and iso-valerate concentrations were reduced as RUP: CP increased (p < 0.05), and propionate concentration showed a similar trend (p = 0.062). In conclusion, optimizing RUP levels in the diets of fattening Hu sheep significantly enhances growth performance without compromising feed efficiency or the overall rumen fermentation process. These findings provide a foundation for developing feeding strategies that maximize production efficiency in sheep farming.