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 protein requirements of lactating goats. Small Ruminant Research. 53:327-337.
Interpretive Summary: A database of treatment mean observations was constructed from available goat feeding and nutrition research publications. Metabolizable protein for lactation (MPl) was determined by applying assumptions of crude protein degradability properties and energy from ruminal fermentation of dietary ingredients and partitioning of protein used for maintenance functions and lost or gained as body weight. Regression of MPl against milk protein yield (MkP) indicated 1.45 g of MPl required per 1 g of MkP, or a milk protein efficiency of 0.69. Because of the appreciable size of the database used to derive these estimates, they should be of value in describing MPl needs of goats as well as predicting performance.
Technical Abstract: Data from 30 studies with 173 treatment mean observations of lactating goats were used to determine metabolizable protein (MP) requirements for lactation (MPl). Milk protein yield (MkP) was calculated from milk yield and protein concentration. MP was estimated from dietary ingredient composition and a feedstuff database of CP degradability properties and ruminal fermentable energy concentration. MPl was estimated with a factorial method by subtracting MP used for maintenance, which was the sum of scurf (0.2 g/kg BW0.6), endogenous urinary (1.03 g/kg BW0.75) and metabolic fecal CP losses (2.67% DM intake) divided by an efficiency of use of MP for maintenance of 1.0. Also, MP was adjusted for BW change (14.3% protein), assuming an efficiency of MP use for protein accretion of 0.59 and that mobilized tissue protein was used for lactation with the same efficiency as MP from the diet or microbial cells. The equation for the regression of MPl (g/day) against MkP (g/day) was: MPl = 15.2 (S.E. = 7.77) + 1.30 (S.E. = 0.090) x MkP (n = 163, adjusted-R2 = 0.56); the intercept was not different from zero (P > 0.05). The slope of a no-intercept equation (regression line forced through the origin) was 1.45 (S.E. = 0.033). In conclusion, these results suggest a MPl requirement for goats of 1.45 g/g of MkP or a milk protein efficiency of 0.69. Because of the approach employed, application of this MPl requirement should not include provision of additional MP as a safety factor. With the large number of observations in this database, this requirement estimate should be of value in expressing protein needs and predicting performance of lactating goats, although future research to refine assumptions may improve accuracy.