The effect of avoparcin on the ileal and faecal digestibility of nitrogen and amino acids in the milk-fed calf

Abstract

ABSTRACTThe study aimed to determine the effect of the growth promotant avoparcin on the digestion and absorption of nitrogen and amino acids from pre-ruminant milk-fed calves. Eighteen male Friesian calves, 45 kg live weight, were allocated to three diets: a commercial high-quality milk replacer compound (control); control with 100 mg zinc bacitracin per kg (positive control) and control with 40 mg avoparcin per kg. The diets were given once-daily at a set rate of intake during a 14-day metabolic study. On the 15th day the calves were fed at 2-h intervals and ileal digesta were sampled (8 h after the start of feeding) from the euthanazed animal. Estimates of apparent ileal digestibility were determined by reference to an indigestible marker, with the comparable faecal estimates determined following the total collection of faeces.There was no significant effect of avoparcin or zinc bacitracin addition on faecal apparent digestibility of dry matter, nitrogen, gross energy and amino acids or on ileal apparent digestibility of nitrogen and amino acids. Neither was there a significant effect of either additive on nitrogen retention, daily urinary urea and total nitrogen excretions or portal and peripheral plasma urea concentrations. Ileal apparent digestibility coefficients determined on the control diet ranged from 0-82 for glycine to 0-96 for phenylalanine, tyrosine and methionine. The ileal measures of apparent digestibility were more variable than the comparable values determined over the entire digestive tract. Measurements on the faeces compared with measurements on digesta at the terminal ileum gave higher values (P< 0·05) of apparent digestibility for nitrogen and 10 of the 16 amino acids.