Effect of sugarcane genotype and maturity stage at harvest on feed intake and ruminal parameters of growing steers

This experiment was conducted to evaluate the effect of altering fibre digestibility by genotype and maturity stage of sugarcane silage on intake, ruminal fermentation, ruminal kinetics, and rumen bacteria populations. Two genotypes with high or low NDF digestibility (NDFD) harvested for silage at early or late maturity were used in a 2 x 2 factorial arrangement of treatments: two genotypes and two maturity stages. Eight ruminally cannulated Nellore steers were used in a duplicated 4 x 4 Latin square design. Experimental diets were formulated with 40% sugarcane silage on DM basis. The DMI was greater when the animals were fed early-maturity sugarcane silage, but only with low-NDFD genotype. Intake of aNDFom was greater for early-maturity sugarcane diets than late-maturity sugarcane diets. Rumen pool of DM, aNDFom and iNDF were greater when diets with the low-NDFD genotype were fed. Turnover of aNDFom and daNDFom (digestible aNDFom), and aNDFom passage rate were greater when animals were fed high-NDFD sugarcane silage. Passage rate of aNDFom was greater when early-maturity sugarcane silage was provided. Ruminal pH was greater when early-maturity silages were fed, but only with high-NDFD genotype. Total SCFA concentration in the rumen was greater when early-maturity silages were fed, but only with low-NDFD genotype. Proportion of propionate was greater in the rumen of animals fed high-NDFD sugarcane genotype compared to animals fed low-NDFD sugarcane genotype. Megasphaera elsdenii population was greater when diets with late-maturity sugarcane silages were fed. There was a tendency for greater relative populations of Fibrobacter succinogenes and Ruminococcus albus when animals were fed low-NDFD sugarcane silage. In conclusion, feeding growing steers with high-NDFD sugarcane silage can positively affect rumen pool through faster passage rate and turnover of fibre that might benefit intake when metabolic pathways are not driving satiety. (AU)