Abstract
Empty body and carcass chemical composition were determined in 67 Nellore bulls from Selection Nellore (NeS) and Control Nellore (NeC) herds of an animal breeding program for growth, slaughtered at 570 days of average age, after 100 days of feedlot. Selection Nellore animals had, respectively, 360 and 430 kg of initial and slaughter body weight, and NeC animals had 318 and 373 kg for the same traits. Animals were slaughtered and empty body composition was determined by chemical analysis of the components blood, hide, head and feet, viscera and carcass. Tissue deposition rates and gain chemical composition were also determined based on gains estimated by comparative slaughter technique. Significant differences were detected between NeS and NeC animals for slaughter body weight, empty body weight, empty body gain rate, and contents of water, protein, ash and retained energy in empty body, showing that selected animals had greater body sizes and growth rates. There were no significant differences in fat contents in empty body and carcass, suggesting that selected animals had higher growth rates as compared with the control, and were slaughtered with good body and carcass fat contents in the same feedlot time. Control Nellore animals showed a 10% higher gain in fat percentage than NeS in the period. This shows that the growth of bone and muscle ceased earlier and NeC group accumulated more fat. Animals selected for growth have heavier carcasses and greater tissue deposition rates with proportional composition similar to unselected animals.
Highlights
Modern animal husbandry is aimed at maximizing productivity and the generation of profits
Residual feed intake (RFI) was calculated as the difference between observed individual dry matter intake and predicted intake using regression equations developed as a function of mean metabolic body weight and average daily gain: estimated DMI = –1.301015+2.3 00828*ADG+0.091755*BW0.75 (r2 = 0.89) for 2007, and estimated DMI = –0.95165+2.5576*ADG + 0.081*BW0.75 (r2 = 0.89) for 2008, in which DMI is dry matter intake, BW0.75 is the mean metabolic body weight and ADG is the average daily weight gain observed throughout the experiment
The differences observed between the NeS and NeC herds are a consequence of the selection for growth to which the herds were subjected, since both herds originated from the same base population
Summary
Modern animal husbandry is aimed at maximizing productivity and the generation of profits. Bonilha et al (2007), studying animals of the same origin, found no differences in relative water, ether extract or protein amounts between the NeS and NeC groups.
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