Influence of direct-fed fibrolytic enzymes on diet digestibility and ruminal activity in sheep fed a grass hay based diet

¹ Departamento de Producción Animal. Universidad de León 24071 León, Spain; Universidad Nacional de Colombia, Sede Medellín, Facultad de Ciencias Agropecuarias, Colombia
² Departamento de Producción Animal. Universidad de León 24071 León, Spain

^* To whom correspondence should be addressed. E-mail: mdcart{at}unileon.es.

	Abstract

Six rumen-fistulated Merino sheep were used in a crossover design experiment to evaluate the effects of an exogenous fibrolytic enzyme preparation (12 g/d; ENZ), delivered directly into the rumen, on diet digestibility, ruminal fermentation and microbial protein synthesis. The enzyme presented endoglucanase and xylanase activities. Sheep were fed a mixed grass hay:concentrate (70:30; DM basis) diet at a daily rate of 50 g/kg BW^0.75. Samples of grass hay were incubated in situ in the rumen of each sheep to measure DM and NDF degradation. The supplementation with ENZ did not affect diet digestibility (P = 0.30 to 0.66), urinary excretion of purine derivatives (P = 0.34), ruminal pH (P = 0.46), or concentrations of NH₃-N (P = 0.69) and total VFA (P = 0.97). In contrast, molar proportion of propionate was greater (P = 0.001) and acetate:propionate ratio was lower (P < 0.001) in ENZ-supplemented sheep. In addition, ENZ supplementation tended to increase (P = 0.06) numbers of cellulolytic bacteria at 4 h after feeding. Both the ruminally insoluble potentially degradable fraction of grass hay DM and its fractional rate of degradation were increased (P = 0.002 and 0.05, respectively) by ENZ treatment. Supplementation with ENZ also increased (P = 0.01 to 0.02) effective and potential degradability of grass hay DM and NDF. Ruminal fluid endoglucanase and xylanase activities were greater (P < 0.001 and 0.03, respectively) in ENZ-supplemented sheep than in control animals. ENZ supplementation did not affect either exoglucanase (P = 0.12) or amylase (P = 0.83 activity. The results indicate that supplementing ENZ directly into the rumen increased the fibrolytic activity and stimulated the growth of cellulolytic bacteria without a pre-feeding feed-enzyme interaction.

Key Words: enzymatic activity, fibrolytic enzymes, microbial protein synthesis, ruminal fermentation