Metabolizable protein requirements of lactating goats

I. V. Nsahlai^1,2, A. L. Goetsch¹, J. Luo¹, and T. Sahlu¹

¹E (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK 73050
²Department of Animal and Poultry Science, University of Natal, Scottsville, R. South Africa

Data from 31 studies with 174 treatment mean observations from goats in different stages of lactation were used to determine the metabolizable protein (MP) requirement for lactation (MP_l). Milk protein yield (MkP) was calculated from milk yield and protein concentration. The MP supply, the sum of digestible ruminally undegraded dietary and microbial true protein, was estimated from ingredient composition and a database of CP degradability properties and ruminal fermentable energy concentration derived from literature values when not provided in the original publication. MP_l was estimated from MP by subtracting MP used for maintenance functions (scurf (g CP), 0.2 x kg BW^0.6; endogenous urinary (g CP), 1.031 x kg BW^0.75; metabolic fecal (CP), 2.67% DM intake; 67% efficiency of use) and adjusting for BW change (14.3% protein). MP_l was regressed against MkP, and after removing observations with residuals greater than 1.5 times the residual SD, the refitted equation was: MP_l = 10.2 (SE = 8.13) + 1.18 (SE = 0.095) x MkP (n = 149, adjusted R² = 0.51); the intercept was not different from zero (P > 0.05). Based on a no-intercept equation, 1.30 (SE = 0.034) g of MP_l were required for 1 g of MkP, corresponding to milk protein efficiency of 0.77. In conclusion, these results suggest an MP_l requirement for goats of 1.30 g/g of MkP. Although this approach and estimate of the MP_l requirement should have utility in expressing needs for protein and(or) predicting milk production by lactating goats, improvements in accuracy from refined assumptions are desirable and will likely occur with future research. Supported by USDA project No. 9803092.