The effects of genetic group and nutritional level on relative size of internal organs were studied. Sixty-three bulls, 16 Gyr, 16 Guzera, 15 Nellore and 16 Mocho de Tabapuã, averaging twenty four months of age, and initial live weight of 376.4, 357.6, 362.0, and 368.6 kg, respectively were used. The animals from each breed were randomly assigned to five groups. One group was immediately slaughtered (AB), three groups were full fed, in individual free stall, a diet containing 50% of concentrate on dry matter basis (group1, 2 and 3), and one group was fed with a restricted amount of the same diet to supply the levels of protein and energy 15% above maintenance (AR). The animals of groups 1, 2 and 3 were slaughtered when they reached the individual live weights of 405, 450 and 500 kg, respectively. At slaughter, the empty body weight (EBW) was determined and the weight of internal organs and viscera were recorded. There were no differences among breed regarding to weight of liver, spleen, small and large intestines, reticulo-rumen, omasum, stomach and gastrointestinal tract (GIT), per 100 kg of EBW. The feed restriction did not affect the weights of heart and lungs, but reduced the weight of liver and GIT components
nutritional level; internal organs; relative size; gastrointestinal tract; zebu cattle
