Effects of α-ketoglutarate and its calcium salt on growth performance, health, rumen fermentation and microbiota in fattening Hu lambs

Rumen microbes govern energy supply and nitrogen use in sheep. α-Ketoglutarate (AKG) links carbon and nitrogen metabolism and may support microbial synthesis, yet its in vivo effects on fermentation, digestibility, and antioxidant status in fattening lambs remain unclear. This study investigated the effects of AKG and its calcium salt (Ca-AKG) on growth performance, antioxidant capacity, nutrient digestibility, rumen fermentation, and rumen microbiota in fattening Hu lambs. Eighteen 3-month-old male Hu lambs (22.2 ± 1.08 kg) were randomly assigned into three groups (n = 6): (1) control group, fed a basal diet; (2) AKG group, fed the basal diet + 0.5% AKG (DM basis); and (3) Ca-AKG group, fed the basal diet + 0.5% Ca-AKG (DM basis). The experimental period lasted 9 weeks, including a 2-week adaptation phase followed by a 7-week measurement period. No treatment × week interaction was observed for growth performance, rumen fermentation, or blood biochemical parameters (P > 0.05). AKG tended to increase average daily gain (ADG) and gain-to-feed ratio (G: F) in fattening Hu lambs (0.05 < P < 0.10), but did not affect final BW (P > 0.10). In contrast, Ca-AKG improved DM intake, ADG, G: F, and final BW (P < 0.05). AKG increased rumen butyrate concentration and apparent digestibility of NDF, ADF, and ether extract, while Ca-AKG elevated butyrate, total volatile fatty acid (VFA) concentration, and ether extract digestibility (P < 0.05). Neither treatment affected organic matter digestibility nor rumen pH (P > 0.05). Both AKG and Ca-AKG reduced plasma bicarbonate and glucose but increased triglycerides (P < 0.05). Significant treatment × week interactions were observed for plasma superoxide dismutase and catalase (P < 0.05). AKG reduced superoxide dismutase activity at week 4 (P < 0.05), but not at week 7 (P > 0.05). Ca-AKG decreased superoxide dismutase activity (P < 0.05) at week 4 without affecting catalase activity (P > 0.05); however, it enhanced both enzymes at week 7 (P < 0.05). Neither treatment altered alpha or beta diversity of rumen bacteria (P > 0.05). However, Ca-AKG increased Bacteroidetes and decreased Firmicutes at the phylum level (P < 0.05), elevated Prevotella and Prevotellaceae-UCG-003, and reduced Quinella, Christensenellaceae-R-7 group, and Aeromonas at the genus level. In summary, Ca-AKG more effectively promotes VFA synthesis, enhances plasma antioxidant capacity, and improves growth performance than AKG in fattening Hu lambs.