Effects of feed intake-regulated nutritional compensation strategies on growth performance, blood indices, and rumen microbiota of Gangba sheep.

Feed intake-regulated nutritional compensation improves feed efficiency in sheep; however, its relevance and underlying mechanisms in high-altitude indigenous breeds such as Gangba sheep remain unclear. Ninety-six four-month-old healthy male Gangba sheep (16.20 ± 0.61 kg) were randomly assigned to four groups (six replicates per group, four sheep per replicate): ad libitum feeding (ALF) and low-, medium-, and high-restriction feeding groups (LRF, MRF, and HRF), receiving 85%, 70%, and 55% of ALF intake, respectively, for 30 d, followed by 60 d of compensatory refeeding. During the restriction period, increasing restriction intensity decreased body weight at d 30, average daily feed intake, and average daily gain (P < 0.05) and increased the feed-to-gain ratio (P < 0.001). Medium and high restriction also decreased total antioxidant capacity (P = 0.010), immunoglobulin A (P < 0.001), immunoglobulin M (P = 0.045), neutral detergent fiber digestibility (P = 0.004), ruminal papilla height (P = 0.006), and ruminal butyric acid concentration (P = 0.013). Over the whole experimental period, feed intake-regulated nutritional compensation significantly reduced average daily feed intake compared with ALF (P < 0.001). The feed-to-gain ratio was lower in the LRF group than in the ALF group (P = 0.004), indicating improved feed efficiency under low restriction feeding. Restriction feeding also induced adaptive changes in gastrointestinal development and rumen microbial diversity, with microbial α diversity recovering after refeeding while community structure remained differentiated among treatments. Overall, low feed restriction (85% of ALF) enhanced feed utilization while maintaining physiological homeostasis in Gangba sheep under forage-limited high-altitude conditions.