Metabolizable protein requirements of lactating goats
I. V. Nsahlai, I. V., A. L. Goetsch, J. Luo, J. E. Moore, Z. B. Johnson, T. Sahlu, C. L. Ferrell, M. L. Galyean, and F. N. OwensSmall Ruminant Research 53:327-328. 2004.
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 (MPl). Milk protein yield (MkP) was calculated from milk yield and protein concentration. MP 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. MPl was estimated from MP by subtracting MP used for maintenance functions (scurf, endogenous urinary and metabolic fecal) and adjusting for BW change. MPl was regressed against MkP, and after removing observations with residuals greater than 1.5 SE, the equation was: MPl = 10.2 (SE = 8.13) + 1.18 (SE = 0.095) × 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 MPl was required for 1 g MkP, corresponding to milk protein efficiency of 0.78. A regression of observed values against ones predicted from the no-intercept equation had an intercept and slope not different from zero and one, respectively (P > 0.05). In conclusion, even with an appreciable number of assumptions from literature other than original publications to estimate MPl, there appears potential to reasonably well predict MPl requirements of lactating goats. These results suggest an MPl requirement of 1.30 g/g MkP. Although this approach and estimate of the MPl requirement should have utility in expressing protein needs of or predicting milk production by lactating goats, improvements in accuracy with future research to refine assumptions are desirable and expected.
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