Effects of Concentrate Level and Combined Use of Virginiamycin and Salinomycin on Nutrient Intake and Digestibility of Nellore Steers

Abstract Text: Eight ruminally cannulated Nellore steers (434 ± 35 kg initial BW) were allotted to a 4x4 replicated Latin square design (21-d periods) to evaluate the effects of concentrate and virginiamycin levels in diets containing salinomycin on nutrient intake and digestibility. Treatments were arranged as a 2x2 factorial, with 2 concentrate levels (70C and 90C diets had 70 and 90% concentrate, respectively) and 2 virginiamycin levels (0 and 15 ppm) in the diet DM. Steers were fed once daily at 0800 and salinomycin was included in all diets (13 ppm). The 70C diet contained 33% starch, 16% CP, and 31% NDF, whereas the 90C diet contained 47% starch, 16% CP, and 19% NDF on DM basis. Dry matter, CP, NDF, and starch intakes were calculated as the difference between the amount of nutrient offered and refused. Apparent digestibilities of nutrients were determined by total fecal collection for 3 d on each experimental period. Statistical analyses were performed using the MIXED procedure of SAS. No interactions between concentrate and virginiamycin levels were observed for any analyzed variable. Steers receiving the 90C diet showed greater (P ≤ 0.01) DM (7.73 and 8.23 ± 0.19 kg/d for 70C and 90C, respectively), CP (1.24 and 1.32 ± 0.03 kg/d for 70C and 90C, respectively), and starch intakes (2.58 and 3.78 ± 0.13 kg/d for 70C and 90C, respectively), whereas NDF intake was greater (P ≤ 0.01) for steers fed the 70C diet (2.28 and 1.57 ± 0.07 kg/d for 70C and 90C, respectively). Intake variables were not affected by virginiamycin inclusion. Animals receiving the 90C diet showed greater (P < 0.01) apparent digestibilities of DM (66.21 and 73.70 ± 0.94 % for 70C and 90C, respectively) and CP (71.23 and 77.35 ± 0.83 % for 70C and 90C, respectively), whereas NDF and starch digestibilities did not differ between concentrate levels. Steers fed only salinomycin showed greater (P = 0.05) starch digestibility in comparison with those receiving both additives (90.90 and 88.98 ± 0.78 % for 0 and 15 ppm virginiamycin, respectively). There were no effects of virginiamycin inclusion on DM, CP, and NDF digestibilities. In conclusion, nutrient intake and apparent digestibility of Nellore steers are affected by dietary concentrate levels, whereas the effects of the combined use of virginiamycin and salinomycin on these variables are less pronounced.

Keywords: antibiotic; ionophore; Zebu cattle