Abstract: 【Objective】 The aim of this experiment was to evaluate the effects of α-ketoglutaric acid (AKG) on rumen fermentation, nutrient digestion and metabolism, and blood biochemical parameters in sheep, to provide a reference for AKG as a regulator of rumen fermentation in ruminants.【Method】 Five healthy small-tailed Han rams with permanent rumen fistulas were used in a 5×5 Latin square design, with each animal receiving a basal diet (the ratio of concentrate to roughage was 55:45) supplemented with AKG at doses of 0, 25, 50, 100 and 200 mmol per day, respectively;The experimental consisted of 5 phases, each experimental phase lasted for 24 days, including a 14-day adaptation period, a 7-day digestion and metabolism test period, and a 3-day ruminal fluid sampling period.Jugular venous blood was collected 1.5 h after morning feeding on the first day of the ruminal fluid sampling period.All feces and urine were collected during the digestion and metabolism test period to determine apparent digestibility of nutrients and nitrogen, calcium, and phosphorus metabolism.Rumen fluid was used to determine fermentation parameters and protozoan counts, and blood was used to determine physiological and biochemical parameters.【Result】 AKG had no significant effect on NH₃-N, valerate, and isovalerate levels in rumen fluid (P>0.05).The rumen fluid pH decreased linearly with the increase of AKG addition (P<0.05).The number of protozoa and the ratio of acetate to propionate showed a quadratic effect with an increasing and then decreasing (P<0.05), and acetate, propionate, and total volatile fatty acids showed a quadratic effect with a decreasing and then increasing with the increased dose of AKG supplementation (P<0.05).The addition of AKG had no significant effect on the apparent digestibility of dry matter, organic matter, crude protein, crude fat, calcium, phosphorus, neutral detergent fiber, and acid detergent fiber, and the metabolism of nitrogen, calcium, and phosphorus (P>0.05).AKG had no significant effect on blood albumin and urea nitrogen concentrations, and the activities of aspartate aminotransferase and alanine aminotransferase (P>0.05).With the increased of AKG addition, the total protein concentration in blood showed a quadratic effect with increasing and then decreasing (P<0.05).【Conclusion】 The addition of AKG to sheep diets acted mainly in the rumen, lowering the pH of the rumen fluid, 50 mmol/d AKG reduced the production of propionate and total volatile fatty acids, improved the ratio of acetate to propionate, and increased the concentration of total protein in the blood.

Key words: α-ketoglutaric acid; sheep; rumen fermentation; digestion and metabolism; blood biochemical indicators