Feed intake and nitrogen utilisation by growing goats fed by-product based diets of different protein and energy levels

Nine local (Guyana, South America) cross-bred, intact, growing, male goats (6 months old with mean (+/- SD) initial BW of 19.9 +/- 2.8 kg) were used in two metabolism trials. They were fed diets formulated to be iso-caloric with protein levels of 51, 76, 91, 108 and 127 g CP kg(-1) DM (Trial 1). Trial 2 goats were fed diets formulated to be iso-nitrogenous with energy density values of 7, 11, 12, and 14 MJ DE kg(-1) DM, Diets contained ground untreated sugarcane bagasse as the sole roughage source ranging from 253 to 540 g kg(-1) DM. Each diet was pelleted to minimise differences in physical-form and to prevent sorting and selection. The overall mean DMI values (+/-SD) for Trials 1 and 2 were 25.0 +/- 1.4 and 29.8 +/- 4.1 g kg(-1) BW, respectively. Trial 1 DMI showed a (P < 0.001) linear increase with N intake which accounted for 56% of the variation of DMI and an increase of 33.1 g per unit increase of N, Both OM and DE intake increased (P < 0.05) with increasing dietary protein levels. However, when diets of varying energy levels (Trial 2) were fed only DE intake increased (P < 0.05), DMI increased to 11 MJ DE kg(-1) DM but fell when dietary energy was increased to 14 MJ DE kg(-1) DM. Digestibility of DM, OM and N showed (P < 0.001) differences, Urine N output and N retained increased (P < 0.01) with increasing dietary CP levels. This trend was not noted with increasing dietary energy levels. Urine N output decreased (P < 0.01) with increasing dietary energy levels. Diets with the lowest dietary energy level had less (P < 0.05) N retention. It was concluded that growing local goats can be fed a complete pelleted by-product based diet under confinement, and obtain adequate levels of DMI and nutrient utilisation.