Abstract
The aim of this study was to predict the body and carcase composition of Nellore heifers and their crosses with Angus and Simmental bulls. Sixty heifers from three genetic groups were used, 20 Nellore, 20 Nellore x Angus and 20 Nellore x Simmental; of these, 12 (four from each genetic group) were slaughtered at the beginning of the experiment (reference group). The heifers were randomly divided into nine treatments (completely randomised design), in a 3 x 3 factorial scheme of three genetic groups and three diets (30 and 50% of the dry matter of the concentrate feed, in addition to the maintenance group) in feedlot. Twelve heifers (four from each genetic group) were fed at maintenance level (1.1% of body weight in dry matter) with a diet containing 30% concentrate, and 36 heifers (12 animals from each genetic group) were fed ad libitum, with 30% (six from each group) or 50% (six from each group) of the dry matter (DM) from the concentrate feed. After slaughtering, the right-side half-carcase was completely dissected, and the 9 th, 10 th and 11 th ribs removed, from the left-side half-carcase, were cut. The 9 th, 10 th and 11 th rib cut satisfactorily estimated the fat and bone content; however, the muscle content was underestimated by 5.32%. The 9 th, 10 th and 11 th rib cut also satisfactorily estimated the chemical composition of the body and carcase, but not the physical composition of the carcase of Nellore heifers or their crosses with Angus and Simmental. The chemical constituents of the empty body and carcase are adequately estimated from the 9 th, 10 th and 11 th rib cut when the equations proposed by Valadares Filho, Paulino and Magalhaes (2006) are used. The percentage of macrominerals can be estimated from the rib cut, however, the levels of calcium, phosphorus and magnesium are the most accurate.
Highlights
The main body components of cattle are the muscles, fats, bones, organs and viscera, and all of these are composed of varying amounts of proteins, lipids, water and minerals
Obtaining the composition of carcase tissue results in high experimental costs (COSTA et al, 2014; CUNHA et al, 2008; FERNANDES et al, 2008; FERNANDES et al, 2010), besides being an extremely laborious process, as directly obtaining carcase and/ or empty body composition requires the complete dissection of at least half of the carcase (BONILHA et al, 2011; COSTA; SILVA et al, 2013; CUNHA et al, 2008; MAIA et al, 2014; MITCHELL, 2007)
The heifers were randomly divided into nine treatments, in a 3 x 3 factorial scheme of three genetic groups and three diets, with six replications per treatment for the animals kept ad libitum and four for those kept at maintenance level
Summary
The main body components of cattle are the muscles, fats, bones, organs and viscera, and all of these are composed of varying amounts of proteins, lipids, water and minerals. Determining body composition is fundamental for identifying changes in growth composition, and this is influenced by various factors such as race, age, sex and diet composition. In addition to identifying changes during the growth of the animals, characterising body composition is the first step in determining the nutritional requirements of cattle. Knowledge of tissue growth patterns and nutritional requirements makes it possible to balance feed and supplement for specific levels of performance, as well as to estimate performance from balanced diets based on requirements. The use of indirect methods that might predict body and carcase composition is extremely useful (MORAIS et al, 2016), making it possible to evaluate the effect of any type of treatment the animals may have undergone, and to verify the impact on the carcase and empty body
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