Anise and capsicum as alternatives to monensin to modify rumen fermentation in beef heifers fed a high concentrate diet

Four Holstein heifers (229 ± 24 kg BW) fitted with ruminal trocars were used in a 4 × 4 Latin square design experiment to evaluate effects of monensin (MON), anise extract (ANI) and capsicum (CAP) on rumen microbial fermentation. Heifers were fed a 100:900 forage:concentrate diet (157 g CP/kg and 223 g NDF/kg on a dry matter (DM) basis). Treatments were: no extract (CTR), 238 mg/d of MON, 500 mg/d of ANI or 500 mg/d of CAP. Each period consisted of 15 d of adaptation and 9 d of sampling. From d 16 to 21 of each period, DM intake was measured while, from d 22 to 24, ruminal contents were sampled 0, 4, 8 and 12 h after feeding to determine ruminal pH, volatile fatty acids (VFA) concentration, large peptide (LPep), small peptide plus amino acid (SPep + AA), and ammonia N. Statistical differences were declared if P<0.05. Monensin reduced VFA from 112.6 to 108.8 mM, acetate proportion from 55.3 to 54.4 mol/100 mol, acetate to propionate ratio from 2.03 to 1.92 mol/100 mol, branch-chained VFA (BCVFA) from 2.5 to 2.1 mM, NH3 N from 15.3 to 13.4 mg/100 ml, protozoa counts from 5.69 to 5.46 log10 counts/ml, and increased propionate proportion from 25.2 to 27.5 mol/100 mol, SPep + AA N from 15.3 to 18.1 mg/100 ml and LPep N from 11.2 to 14.3 mg/100 ml versus control. Capsicum increased DM intake from 6.57 to 7.42 kg/d and butyrate proportion from 13.0 to 14.1 mol/100 mol, and reduced acetate proportion from 55.3 to 54.0 mol/100 mol versus control. Anis reduced VFA from 112.6 to 110.8 mM, BCVFA from 2.5 to 2.1 mM and NH3 N from 15.3 to 13.6 mg/100 ml, acetate proportion from 55.3 to 53.5 mol/100 mol, acetate to propionate from 2.03 to 1.90, protozoa counts from 5.69 to 5.56 log10 counts/ml, and increased propionate proportion from 25.2 to 26.9 mol/100 mol and SPep + AA N from 15.3 to 18.0 mg/100 ml versus control. Capsicum may be useful in stimulating appetite, and ANI and MON had similar effects on rumen fermentation except for changes in molar proportion of butyrate, which suggests that they have a different mode of action.