Metabolizable energy requirements of lactating goats

Abstract

Data from 44 studies with 243 treatment mean observations, representing 2476 goats in various stages of lactation, were used to estimate the requirement and efficiency of use of ME for milk production. Development and evaluation data subsets comprised, respectively, 68 and 32% of observations. ME intake was also adjusted for energy lost in excretion of excess nitrogenous compounds in urine (ME ExN), as 62.21 kJ/g of N intake above endogenous urinary N (0.165 g/kg BW 0.75). Adjusted ME intake was partitioned into that used for maintenance and activity in pen or stall settings (ME m; by two methods), ME secreted in milk and ME gained as BW. For Method 1, ME m = 1.1×315 kJ/kg BW 0.75/ k m, with k m or efficiency of ME use for maintenance = 0.503 + (0.019×ME,MJ/kg DM). For Method 2, estimates of ME m in a companion study for dairy (501.3 kJ/kg BW 0.75) and other goat biotypes (422.7 kJ/kg BW 0.75) were used. When BW increased, ME intake was adjusted for tissue accretion (efficiency = 0.75) to derive dietary ME used in milk secretion (ME l-d). Milk yield was corrected to 4% fat [4% FCM;MJ/kg = 1.4694 + (0.4025 × % milk fat)]. For does decreasing in BW, FCM from the diet (FCM d) was estimated by adjusting for use of mobilized tissue energy (23.9 kJ/g; efficiency = 0.84). No particular equations explained considerably more variability in observed FCM or NE for lactation than other equations. Based on no-intercept regressions (ME l-d against FCM d) with Method 1, the dietary ME requirement for lactation was 4598 (S.E. = 106.6) and 4937 (S.E. = 106.5) kJ/kg FCM with and without adjustment for ME ExN, respectively. With Method 2 and no-intercept equations, the dietary ME requirement for lactation was 4882 (S.E. = 105.2) and 5224 (S.E. = 105.8) kJ/kg FCM with and without adjustment for ME ExN, respectively. Prediction accuracy was similar between methods and improved slightly by correction for ADG. In conclusion, with the large amount of data employed in this study, these estimates and this factorial approach seem useful to predict energy requirements of lactating goats, with potential for future enhancements based on research of the factorial approach assumptions.