Effect of Ractopamine hydrochloride and dietary protein content on performance and carcass traits of Nellore bulls
The objective of this research was to evaluate the effects of ractopamine hydrochloride (RH) and dietary crude protein (CP) on performance and carcass traits of Nellore young bulls. Forty eight Nellore bulls were grouped by BW, and randomly assigned to treatments in a 2x2 factorial arrangement of treatments. The factors were two levels of dietary CP (100 and 120% of MP requirement), and two levels of RH (0 and 300 mg/animal/d). Treated animal received RH for the final 35d before slaughter. Dry matter intake was measured and adjusted daily. The animals were weighed at intervals of 21 d, at the beginning of supplementation, after 18 d of supplementation and before slaughter. Feed efficiency was calculated from ADG and DMI. On d 113 hot carcass weights were recorded at slaughter. After 24 h of chilling, longissimus muscle area (LMA), and fat thickness were measured at the left half-carcass. The statistical analyses were conducted using SAS, version 9.1.2 for Windows. There was no effect of RH supplementation on final BW (P = 0.26). However, animals supplemented with RH had 19% greater ADG than control animals (1.51 vs. 1.27 kg/d, P = 0.03), this effect was not dependent on the level of CP in the diet (P = 0.43). Increasing dietary CP content above requirements had no effect on final BW, ADG or G:F ratio (P > 0.05). For DM intake, the RH x CP interaction was significant (P = 0.01), where RH supplementation had no effect on DMI at CP100 (P = 0.12) yet it reduced DMI at CP120 (1.95 vs. 1.81 % BW for RH0 and RH300, respectively; P = 0.03). Addition of RH to the diet considerably improved G:F ratio, independently of the CP concentration of the diet (0.15 vs. 0.13, P = 0.02). Treatments had no effect on HCW or dressing percentage of the carcass (P > 0.10). There was a tendency (P = 0.07) for RH supplementation to increase LMA, independently of dietary CP levels (83.2 vs. 87.9 cm2). Ractopamine did not alter fat thickness (P = 0.29); however, increasing dietary CP above requirements (CP120) decreased fat thickness (5.1 vs. 4.3 mm for CP100 and CP120, respectively). In conclusion, ractopamine supplementation increased gain, improved feed efficiency, and increased LMA even in intact Nellore young bulls.
Keywords: Beta-agonist, Cattle, Muscle growth