Effect of dietary glycine and benzoate level on benzoate metabolism in mink (Mustela vison), blue fox (Alopex lagopus), and racoon dog (Nyctereutes procyonoides)

Three 2 x 4 factorial experiments were carried out from August to September with 30 juvenile male mink, 24 raccoon dogs, and 24 blue foxes to investigate the effect of dietary glycine supply (low or high) on the efficiency of these species to excrete hippuric acid with incremental benzoate intake (0, 1, 2, or 4 mmol/kg BW). For mink, two additional treatments with 1 or 2 mmol/kg BW of ethyl benzoate were included. A basal low-glycine diet was formulated to meet the minimum protein requirements of fur animals (30% of ME). This diet was supplemented with 0 or 3 g/kg of glycine, or with 0, 1.0, 2.07, or 4.15 g/kg of sodium benzoate for mink and blue foxes, and with 0 or 4.5 g/kg of glycine and 0, 1.58, 3.17, or 6.34 g/kg of sodium benzoate for raccoon dogs, respectively. Two additional diets with .76 or 1.53 g/kg of ethyl benzoate were made for mink. Fecal and urinary benzoic and hippuric acid excretion were measured for 3 d. The 24-h recovery of [(14)C]benzoic acid injected intraperitoneally was measured from urine, the liver, and the kidneys. All animals appeared healthy and no clinical signs of benzoate overdose were observed. Dietary benzoate level did not affect ADFI or ADG in any species. Glycine supplementation lowered ADFI in mink. The majority of ingested benzoates were absorbed from the gut (over 95%), except in blue foxes, which excreted 6 to 15% of ingested benzoates in feces with incremental increases in benzoate intake. Urinary free benzoic acid excretion accounted for 10% of the ingested benzoates in blue foxes but less than 5% in mink and raccoon dogs. When benzoate intake was 1 mmol/kg BW, mink, blue foxes, and raccoon dogs excreted 71, 77, and 34% of ingested benzoates as hippuric acid in urine, respectively. With higher benzoate intakes, urinary hippuric acid excretion decreased quadratically with mink to 20%, and linearly with blue foxes and raccoon dogs to 45 and 16%, respectively. The hippuric acid pathway appears to be the principal route of benzoate elimination in the mink and blue fox, whereas, in the raccoon dog, other pathways appear to be more important. In mink, the elimination of ethyl benzoate did not differ from that of sodium benzoate. Because glycine conjugation is the primary route of benzoate elimination, it is recommended that benzoate content in fur animal feeds should not exceed 1 g/kg feed on as-fed basis.