Nutrient requirements of goats: Developed equations, other considerations and future research to improve them

A database of treatment mean observations from goat feeding/nutrition studies was constructed and used to develop expressions to describe nutrient requirements of goats. The ME requirement for maintenance (ME_m) was 485, 489, 580, 489 and 462 kJ/kg BW^0.75, and the ME requirement for gain (ME_g) was 13.4, 23.1, 23.1, 19.8 and 28.5 kJ/g ADG for preweaning, growing meat (≥Boer), growing dairy, growing indigenous and mature goats (indigenous and dairy), respectively. The ME_m of mature Angora goats from multiple regression analysis (at 0 tissue gain and clean fiber growth) was 473 kJ/kg BW^0.75; ME requirements for tissue gain and clean fiber growth were 37.2 and 157 kJ/g, respectively. A factorial approach with linear regression was used to determine the dietary ME requirement for lactation of 5224 kJ/kg 4% fat-corrected milk, corresponding to an efficiency of ME use for lactation of 0.59. Metabolizable protein (MP) required for maintenance (MP_m) by mature meat, dairy and indigenous goats was determined as the sum of metabolic fecal (0.0267 g/g DM intake for diets not containing appreciable browse), endogenous urinary (1.031 g/kg BW ^0.75) and scurf CP losses (0.2 g/kg BW^0.6), with an assumed efficiency of MP use for maintenance protein of 1.0. Based on linear regression of MP intake against ADG, for growing goats MP_m was 3.07 g/kg BW^0.75; MP required for ADG (MP_g) was 0.290 g/g ADG for dairy and indigenous goats and 0.404 g/g ADG for meat goats. The MP requirement for lactation was 1.45 g/g milk protein, equivalent to a milk protein efficiency of 0.69. The MP_m of growing and mature Angora goats from multiple regression analysis (at 0 tissue gain and clean fiber growth) was 3.35 g/kg BW^0.75, and MP requirements for tissue gain and clean fiber growth were 0.281 and 1.65 g/g, respectively. Identified areas of research that would yield knowledge allowing development of more accurate estimates of nutrient requirements include composition of accreted and mobilized tissue, effects of stage of maturity and nutritional plane on maintenance energy requirements, energy expenditure due to grazing activity, conditions influencing ruminally undegraded protein and efficiencies of MP utilization.