Substitution effects of Acacia mearnsii leaf-meal for Triticum aestivum bran on nutrient digestibility, rumen fermentation and nitrogen retention in lambs

The study evaluated the effects of substituting increasing levels of Acacia mearnsii leaf-meal (AMLM) for Triticum aestivum bran as the main fibre source in lamb finishing diets on nutrient digestibility, rumen fermentation and nitrogen retention. Twenty-five, three-months-old ram lambs with an average live weight of 25.2 ± 1.41 kg were allocated to one of the five dietary inclusion levels of AMLM (0, 50, 100, 150 and 200 g/kg DM; n = 5) in a completely randomised design for 28 days. Intake and digestibility of dry matter (DM), organic matter and crude protein, main individual and total volatile fatty acids, purine derivatives, supply of microbial nitrogen, and nitrogen intake, retention and utilisation efficiency exhibited quadratic (P ≤ 0.05) responses to AMLM reaching a maximum at 100 g/kg DM inclusion level. Ammonia-nitrogen linearly increased (P ≤ 0.05) with dietary addition of AMLM. Intake and digestibility of neutral detergent fibre (aNDFom) exhibited a positive linear trend (P ≤ 0.05) with graded levels of AMLM in the diet while that of ether extract showed a negative trend. In conclusion, replacement of T. aestivum bran with up to 100 g/kg DM of AMLM in lamb finisher diets can improve digestibility of nutrient, rumen fermentation and retention of nitrogen. •Acacia mearnsii leaf-meal (AMLM) up to 100 g/kg DM improved rumen fermentation.•Digestibility of DM and CP increased quadratically with AMLM addition peaking at 100 g/kg DM.•Dietary AMLM showed a quadratic response to major and total volatile fatty acids.•Nitrogen retention exhibited quadratic trends to AMLM inclusion.•Dietary addition of AMLM linearly increased faecal nitrogen contents.