Effects of Saccharomyces cerevisiae and rumen bypass-fat supplementation on growth, nutrient utilisation, rumen fermentation and carcass traits of lambs

Forty-eight weaned (3 months of age) lambs were randomly distributed in a 2 x 2 factorial design to assess the effect of rumen bypass-fat (RBF) feeding (with and without) and probiotic (Saccharomyces cerevisiae) supplementation (with and without) on growth, nutrient utilisation, rumen metabolic profile and carcass traits during the post-weaning phase (3-6 months of age) of life. The four experimental groups, each having 12 lambs (six male and six female), were thus designated as control (C, basic diet without RBF and probiotic), basic diet without RBF but with probiotic (C + P), basic diet with RBF but without probiotic (C + RBF) and basic diet with RBF and probiotic (C + P + RBF). The basic diet consisted of ad libitum concentrates and dry pala (Zizyphus nummularia) leaves. Additionally, each lamb received 500 g of green ardu (Ailanthus excelsa) leaves. The RBF was calcium salt of fatty acids (source: rice bran oil) and fed at 40 g per kg of concentrate and the probiotic was fed at 9.0 x 10(7) colony-forming units (CFU) per kg bodyweight. Weekly bodyweights were recorded to assess the growth performance of lambs and revealed significantly (P=0.026) higher gain in weight and average daily gain in RBF-supplemented groups independent of probiotic supplementation. The intake of concentrate was higher (P = 0.025) in RBF-fed groups and lead to increased (P = 0.028) total daily dry-matter intake and higher (P < 0.05) plane of nutrition (more metabolisable energy and a higher digestible crude protein intake) irrespective of probiotic supplementation. The feed conversion ratio (FCR) was narrower (P < 0.05) in RBF- and probiotic-supplemented animals. Digestibility of organic matter, ether extract and acid detergent fibre increased and higher nitrogen balance was observed in lambs fed with RBF. Probiotic supplementation showed a positive effect (P < 0.05) on digestibility of acid detergent fibre. Ruminal metabolic profile was assessed at the end of the experimental feeding and it showed higher pH and ciliate protozoa population with RBF, independent of probiotic supplementation. Urinary purine derivatives were measured during the metabolic trial at the end of the experiment, which showed higher allantoin excretion leading to increased microbial nitrogen flow with RBF supplementation. Pre-slaughter weight, loin eye area and lean percentage were higher with a lower bone percentage and cooking loss, showing positive carcass attributes in RBF-fed groups, and the effect of probiotic was non-significant. It is concluded that RBF supplementation enhanced higher intake and utilisation of nutrients that supported improved weight gain, FCR and carcass traits, while Saccharomyces cerevisiae feeding had a positive effect on fibre digestibility and FCR, possibly by modifying the gut environment.