Nutritional requirements of finishing beef cattle: II. Energy requirements for maintenance and weight gain

Pires, C. -Cassol; Fontes, C. -Augusto-De-Alencar; Galvao, J. -Geraldo; Queiroz, A. , C.; Pereira, J. , C.; Paulino, M. -Fonseca

This work was carried out in the Animal Science Department of the Universidade Federal de Vicosa to determine energy requirements for maintenance and weight gain of noncastrated bovines from three genetic groups. Of the 66 bovines used, 22 were Nelore (NE), 22 F1 Nelore times Marchidiana (NM) and 22 F1 Nelore times Limousin (NL) with initial live weights of 252.0, 329.5 and 338,9 kg, respectively. The average age was 20 months. Two animals from each genetic group were lodged in metabolism cages to determine the apparent digestibility of ration energy throughout the experiment. To determine the amount of energy retained in the body, the technique of comparative slaughter was used. Four animals, representative of each genetic group, were slaughtered at the begining of the study. The remaining 16 animals of each genetic group were maintained in single pens and were divided into four sub-groups. The feed of one sub-group was restricted to supply nutrient levels 20% higher than maintenance requirements. The other three sub-groups were full-fed to reach individual slaugther weights corresponding to 90, 100 and 110% of the mature weight of the cows from the corresponding genetic groups. The ration used contained a concentrate to roughage ratio of 50:50. The energy content of the body was estimated by the regression of the logarithm of energy content in empty body weight (EBW) in relation to the logarithm of empty body weight (ARC, 1980). Net energy requirements for maintenance for each breed group were determined using the Lofgreen and Garret method (1968). The net energy requirements for gain were obtained by the deviation of the respective equations for energy content in the body. The NE animals had a lower (P lt 0.01) energy requirement for maintenance (34.17 kcal/EBW-0.75) than the NL (60.03 kdal/EBW-0.75) and NM (67.92 kcal/EBW-0.75) animals, and a higher net energy requirement (P lt 0.01) for weight gain than NL and NM animals.