RESUMO
Forty-eight bulls with an initial body weight (BW) of 408.4⯱â¯22.2â¯kg (ageâ¯=â¯21⯱â¯2â¯months) were used in a randomized complete block design arranged in a 2â¯×â¯2 factorial design. The treatments were diets without virginiamycin (VM-) or with virginiamycin, at 25â¯mg/kg of dry matter (DM, VM+), and diets without crude glycerin (CG-) or with crude glycerin, at 100â¯g/kg DM (CG+). The cold carcass weight and cold carcass dressing (Pâ¯≤â¯0.05) was greater in bulls fed crude glycerin diets. Total unsaturated fatty acids (UFA) were 6.08% higher, and cooking weight loss was 10% lower in bulls fed CG+ diets, compared to bulls fed CG- diets (Pâ¯=â¯0.0081). Crude glycerin at 100â¯g/kg DM could be a suitable replacement for VM, as it led to a slight increase in UFA deposition in meat. However, simultaneous administration of VM and CG did not positively affect performance and carcass traits of feedlot Nellore cattle.
Assuntos
Dieta/veterinária , Glicerol/administração & dosagem , Carne Vermelha/análise , Virginiamicina/administração & dosagem , Ração Animal/análise , Animais , Antibacterianos/administração & dosagem , Composição Corporal , Bovinos , Culinária , Ácidos Graxos/análise , MasculinoRESUMO
The objective of this study was to evaluate the effect of a fresh sugarcane-based diet and different roughage-to-concentrate ratios (70:30, 60:40, 40:60 and 20:80) on the rumen microbiota associated with rumen fermentation parameters and the intake and apparent digestibility of nutrients in Nellore steers. Eight rumen-cannulated Nellore steers (331 ± 8 kg BW) were distributed in a double 4 × 4 Latin square design balanced for the control of the residual effect. The ruminal pH decreased (p < 0.01) and the concentrations of N-NH3, isovaleric and valeric acids increased linearly (p < 0.05) with an increase dietary concentrate level. Furthermore, an increased concentrate proportion reduced the population of Fibrobacter succinogenes and Ruminococus flavefaciens (p < 0.01) and increased the population of Selenomonas ruminantium and Megasphaera elsdenii (p < 0.01). The protozoa count revealed a predominance of the genus Entodinium. The synthesis of microbial N [g/d] and the efficiency of microbial synthesis [g of microbial N/kg of organic matter apparently digested in the rumen] increased as the proportion of concentrate was increased (p < 0.05). Therefore, it can be concluded that an increasing proportion of concentrate in sugarcane-containing diets enhances the synthesis of microbial protein and does not alter the fibre digestibility, although the population of fibre fermenting bacteria was reduced.