Supplementation of Zebu cattle grazing Sahelian pasture. II. Development of body mass and empty body composition

The growth of body mass and changes in empty body composition of three groups of 15 male Zebu cattle (Bos indicus) grazing natural pasture were studied in the Sahelian zone of Mali from 1990 to 1992. The control group (C) grazed natural pasture only, whereas the moderately supplemented group (M) received 0.8-1.5 kg OM/day of crop by-products during the dry season and the first month of the rainy season. Group H (high) was supplemented at 1.2-2.7 kg OM/day in the dry season and at 0.8-1.2 kg OM/day in the rainy season. Applying the deuterium dilution technique, empty body composition was measured at the beginning and end of the rainy season and in mid-dry season, using seasonal factors to correct for fill of the gastrointestinal tract (GIT). Energy retention was calculated from the contents of empty body protein and fat. During the 2 years of study, body mass gains were 143 kg (S.E. 4.9) for group C, 196 kg (S.E. 5.8) for group M and 251 kg (S.E. 6.0) for group H. Total GIT fresh matter content accounted for 166 g (S.E. 4.6) per kg of fasted body mass (FBM) in the dry season and increased to 228 g/kg FBM (S.E. 2.9) at the beginning of the rainy season (P less than or equal to 0.001). Throughout the period of study, the proportion of protein in the empty body varied between average values of 156 g/kg and 179 g/kg, and the proportion of empty body fat ranged from 124-257 g/kg. For all body components, the effect of supplement treatment over time was significantly different between unsupplemented and supplemented animals (P less than or equal to 0.001). From linear regressions between metabolizable energy intake and energy retention the maintenance requirement of grazing cattle was determined at 732 kJ ME/kg(0.75)/day for the dry season and at 522 kJ ME/kg(0.75)/day for the rainy season. It is concluded that the methodological approach yields useful results on empty body composition and energy requirement of Zebu cattle in extensive management systems.