Metabolizable energy requirements of lactating goats

Data from 44 studies with 243 treatment mean observations, representing 2476 goats in various stages of lactation, were used to estimate the requirement for and efficiency of use of ME for milk production. Development and evaluation data subsets comprised, respectively, 68 and 32% of observations. Intake of ME was adjusted for level of feed intake, as 1 - [0.018 × (L - 1)], with L = multiple of the ME requirement for maintenance. ME intake was also adjusted for energy lost in excretion of excess nitrogenous compounds in urine (ExUN), as 33.01 kJ/g of N intake above endogenous urinary N (0.165 g/kg BW0.75). Adjusted ME intake was partitioned into that used for maintenance plus activity [1.1 × 315 kJ/(kg BW0.75 km), with km or efficiency of ME use for maintenance = 0.503 + (0.019 × ME, MJ/kg DM)], ME secreted in milk and ME gained as BW. When BW increased, ME intake was adjusted for tissue accretion (efficiency = 0.75) to derive dietary ME used in milk secretion. Milk yield was corrected to 4% fat [4%FCM; MJ/kg = 1.4694 + (0.4025 × % milk fat)]. For does decreasing in BW, FCM and milk energy from the diet were obtained by adjusting for use of mobilized tissue energy (23.9 kJ/kg; efficiency = 0.84). Based on no-intercept regressions, the dietary ME requirement for lactation was 5017 (SE = 105.3) and 5195 (SE = 94.4) kJ/kg FCM and efficiency of dietary ME utilization for lactation (ME regressed against milk energy) was 0.61 and 0.59 with and without correction for ExUN, respectively. Scatter plots of residuals with the development data subset, and intercepts and slopes that were not different from 0 and 1, respectively, from regressions with the evaluation data subset of observed against predicted FCM and milk energy from the diet, indicated acceptable accuracy and no obvious bias. Therefore, these estimates and this factorial approach seem useful to predict energy requirements of lactating goats, with potential for future enhancements based on research concerning assumptions used in deriving these values.