LAUSR

Abstract Three doses (5, 15 and 30 mg/l in experiment 1; and 100, 250 and 500 mg/d in experiment 2) and three proportions of anise oil (A) and capsicum oleoresin (C; 1A:3C, 2A:2C and 3A:1C) were used to evaluate their effects on rumen microbial fermentation. In experiment 1, a completely randomized block in vitro batch fermentations were conducted in triplicate and in two periods. A 100 ml of a 1:9 ruminal fluid-to-buffer solution were introduced into polypropylene tubes supplied with 0.8 g of DM of a 1:9 forage:concentrate diet (160 g/kg CP, 220 g/kg aNDFom) and incubated for 48 h at 39 °C. Samples were collected to determine fermentation fluid pH and the concentration of volatile fatty acids (VFA) and ammonia N (NH3N). In experiment 2, twelve Holstein heifers (229 ± 24 kg body weight) fitted with ruminal trocars were used in three 4 × 4 Latin squares design. Heifers were fed the same diet as in Experiment 1. Each Latin square was assigned to one of the three doses and animals within square to the different mixes of A and C. Each period consisted of 15 d for adaptation and 9 d for sampling. On d 16–21, dry matter intake was measured. On d 22–24 ruminal content was sampled at 0, 4, 8 and 12 h after feeding to determine ruminal pH and the concentrations of VFA, large peptide (LPep), small peptides plus amino acid (SPep + AA) and NH3 N. Statistical differences were declared at P