Submitted to: Small Ruminant Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2004
Publication Date: 7/1/2004
Citation: Nsahlai, I.V., Goetsch, A.L., Luo, J., Johnson, Z.B., Moore, J.E., Sahlu, T., Ferrell, C.L., Galyean, M.L., Owens, F.N. 2004. Metabolizable energy requirements of lactating goats. Small Ruminant Research. 53:253-273.
Interpretive Summary: With no-intercept regressions and employing metabolizable energy for maintenance (MEm) proposed by AFRC, dietary metabolizable energy (ME) required for milk production was 4937 and 4598 kJ/kg fat corrected milk (FCM) without and after correcting for energy loss in excretion of excess nitrogenous compounds in urine (MEExN), respectively. With the MEm determined from estimates from previous studies, dietary ME required for milk production was 5224 and 4882 kJ/kg FCM without and after correcting for MEExN, respectively. Prediction accuracy was similar between methods and improved slightly by correction for average daily gain. These estimates yielded predictions closely matching observed responses in milk yield and energy with an evaluation data subset and, thus, should have value for describing energy requirements of lactating goats, particularly considering the large size of the database used in this study. However, for proper employment of these requirement expressions, the same approaches for partitioning dietary ME for milk secretion and FCM from the diet is necessary.
Technical 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 (MEE x N), as 62.21 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 and activity in pen or stall settings (MEm; by two methods), ME secreted in milk and ME gained as BW. For Method 1, MEm = 1.1 x 315 kJ/kg BW0.75/km, with km or efficiency of ME use for maintenance = 0.503 + (0.019 x ME,MJ/kg DM). For Method 2, estimates of MEm in a companion study for dairy (501.3 kJ/kg BW0.75) and other goat biotypes (422.7 kJ/kg BW0.75) were used. When BW increased, ME intake was adjusted for tissue accretion (efficiency= 0.75) to derive dietary ME used in milk secretion (MEl-d). Milk yield was corrected to 4% fat [4% FCM;MJ/kg = 1.4694 + (0.4025 x % milk fat)]. For does decreasing in BW, FCM from the diet (FCMd) 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 (MEl-d against FCMd) 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 MEExN, 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 MEExN, 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.