Nutrient requirements of energy and protein for Holstein × Zebu bulls finished in feedlot

Abstract

The objective of this study was to estimate the nutritional requirements of energy and protein in crossbred (Holstein × Zebu) bulls. An experiment of comparative slaughter was conducted with 44 (24 months old) crossbred bulls of 338 ± 39 kg. Bulls were randomly separated as follows: four bulls to the control group, four bulls to the maintenance level group and 36 bulls were fed ad libitum. Corn silage (CS) and sugar cane in natura (SC) at 60 or 40% of dry matter (DM) of total diets were utilized in the diets. The bulls of the last group were randomly assigned to one of six different diets: 1) 60CS:40C(84 days); 2) 60CS:40C (42 days) and 40CS:60C (42 days); 3) 40CS:60C (84 days); 4) 60SC:40C (84 days); 5) 60SC:40C (42 days), and 40SC:60C (42 days), and 6) 40SC:60C (84 days). At the end of the experiment, bulls were slaughtered at Universidade Federal de Viçosa for estimation of the empty body weight. One sample located between the 9th and the 11th ribs of each bull was taken and completely dissected for estimation of the empty body composition using equations developed by BR-CORTE 2010. The data were analyzed as nonlinear models built by means of command NLIN of SAS (version 9.2), adjusted by the method of Gauss-Newton. For all the tests, 0.05 was utilized as critical level for probability of type I error. The net (NEm) and metabolizable (MEm) energy requirements for maintenance were 78.7 and 114.2 kcal/EBW0.75/day, respectively. The equations obtained for NEg and NPg were: NEg (Mcal/day) = 0.0493 × EBW0.75 × EBWG1.0013 and NPg (g/day) = 279.19 × EBWG- 22.8691 × RE, respectively. The model obtained for the percentage of retained energy as protein (%REp) was %REp = 1.7202 × (RE/EBWG)-1.351.