The ratio of milk energy yield to metabolizable energy (ME) intake, i.e. the efficiency of energy utilization for milk synthesis (EMES), is an important measure in lactating goats and is influenced by factors affecting feed intake, digestion, and milk yield and composition. The objective was to investigate relationships between dietary characteristics and level of feed intake, milk composition, and the efficiency of energy utilization for milk synthesis by goats under various production conditions. The dataset that was used in deriving the NRC 2007 requirements for goats was used in this study. Regressions were weighted by the number of individual observations contributing to treatment means. In a regression of dry matter intake in % BW against dietary concentrations of neutral detergent fiber (NDF) and crude protein (CP), including the NDF*CP interaction (p = 0.078) increased the R2 (0.28 vs. 0.25) and decreased the RMSE (root mean square error) slightly (2.08 vs. 2.10). The equation for milk fat yield with the highest R2 (0.45) included BW, concentrations of ME and NDF, and the ME*NDF interaction. In accordance, the equation with the highest R2 (0.43) for milk energy/ME intake was 0.927 + (0.0203*kg BW0.75) – (0.116*ME) – (0.0288*NDF) + (0.00313*ME*NDF). Inclusion in regression equations of interactions between different dietary constituents, particularly NDF, reflects value of considering multiple constituents rather than only single fractions or quality descriptors. The findings suggest potential for improved diet formulation with knowledge of ruminal degradation characteristics of fiber and nitrogenous compounds in individual feedstuffs as well as total mixed diets.
Goetsch et al. (Tue,) studied this question.