Fibrolytic enzyme supplementation through ruminal bolus on eating behavior, nutrient digestibility and ruminal fermentation in Jersey heifers fed either corn silage- or sugarcane silage-based diets

Sugarcane is relatively affordable in subtropical regions and can be used as a forage source for cattle; however, its low fiber degradation in the rumen may impair diet digestibility and animal performance. The objective of this study was to evaluate the influence of a fibrolytic enzyme product in dairy heifers fed either corn silage or sugarcane silage-based diets on nutrient intake and digestibility, eating behavior, energy and N utilization, ruminal fermentation, microbial protein synthesis, and blood metabolites. Twelve Jersey heifers [8±2.5 mo age and 160±15kg of live weight (LW), mean±SD] were assigned to a Latin square design with 2×2 factorial treatment arrangement. Experimental periods had 14days for treatment adaptation, 6days for sampling, followed by 5days of wash out. Treatment sequences consisted of: 1) diet with 549g/kg DM sugarcane silage as forage source (SS); 2) diet with 653g/kg DM corn silage as forage source (CS); 3) sugarcane silage and enzyme product (SSE; Fibrozyme™, Alltech, Nicholasville, KY), SS diet providing heifers with 20g/d enzyme product through ruminal bolus; and 4) corn silage and enzyme product (CSE), CS diet providing heifers with 20g/d enzyme product through ruminal bolus. Enzyme product was supplied once a day before the morning feeding. Heifers fed SS showed lower (P=0.001) nutrient intake than those fed CS. Enzyme product had no effect on feed intake, but it increased (P≤0.048) DM digestibility in heifers. An effect of the interaction between forage and enzyme was observed (P=0.006) on NDF digestibility, in which enzyme supply increased NDF digestibility in 126g/kg DM for heifers fed sugarcane silage. Moreover, enzyme supply increased (P=0.030) the time spent eating of heifers, but it decreased (P=0.012) the efficiency of cud chewing – DM (g/h). No interaction effect was noticed between forage and enzyme on eating behavior measures. Enzyme supply decreased (P=0.012)N absorbed by heifers. An interaction between forage and enzyme was detected on urinary N, in which SSE treatment showed the lowest value of N in urine. Except for the higher (P=0.012) ruminal propionate molar proportion in cows fed CS than those fed SS, no effects (P≥0.212) of forage, enzyme, or forage and enzyme interaction were described on ruminal fermentation measures. Heifers fed sugarcane silage had lower (P=0.008) microbial protein synthesis estimation than those fed corn silage. Enzyme provision increased (P=0.045) urinary urea concentration and excretion (mg/kg LW), and decreased (P≤0.012) daily urea clearance in heifers. In addition, no effect of the interaction between forage and enzyme (P≥0.226) was described on N renal metabolism of heifers. Although the enzyme provision had no effect on NDF digestibility in heifers fed corn silage, it increased NDF digestibility in heifers fed sugarcane silage. The enzyme supply increased the time animals spent eating, but had no effect on ruminal fermentation of heifers.