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Metabolizable protein requirements for maintenance, gain, and mohair fiber growth by Angora goats

J. Luo, A. L. Goetsch, and T. Sahlu

E (Kika) de la Garza American Institute for Goat Research, Langston University, Langston, OK

A database of treatment mean observations from the literature was constructed for Angora goats to estimate metabolizable protein (MP) requirements for maintenance, gain, and mohair fiber growth. Observations were categorized as preweaning, growing, mature (not lactating or pregnant), lactating, and pregnant goats; however, due to limited numbers of observations, data for preweaning, lactating, and pregnant goats were removed. Intake of MP (MPI) was estimated from feed intake, diet composition, and protein degradability properties with methods similar to those of AFRC. Data set 1 (n = 124) was used to determine MP requirements for maintenance and whole body gain (i.e., ADG; tissue and fiber) by simple linear regression; data set 2 (n = 88) was employed to estimate MP requirements for maintenance, tissue gain, and mohair fiber growth by multiple regression. Variables, scaled by kg BW0.75, were MPI (g/d), ADG (g), non-fiber, tissue gain (TG, g/d), and clean fleece growth rate (CFGR, g/d). Because there were no differences (P > 0.05) between growing and mature goats in intercepts or regression coefficients of equations derived from data sets 1 or 2, observations were pooled. Data set 1 was then split into subsets for equation development (n = 73) and evaluation (n = 51). The initial equation for the regression with the development subset was MPI = 4.52 (SE = 0.349) + (0.336 (SE = 0.0568) × ADG) [n = 73; R2 = 0.33]; the final equation after removing five observations with residuals greater than 1.5 times the residual SD was MPI = 4.30 (SE = 0.286) + (0.318 (SE = 0.0471) × ADG) [n = 68; R2 = 0.41]. Regressing observed against predicted values with the evaluation subset resulted in an intercept and slope not different (P > 0.05) from 0 and 1, respectively. The equation with data set 2 was MPI = 3.63 (SE = 0.475) + (0.292 (SE = 0.0538) × TG) + (1.49 (SE = 0.430) × CFGR) [n = 88; R2 = 0.41]. Similarly, after removing observations with residuals greater than 1.5 residual SD, the final equation was MPI = 3.35 (SE = 0.440) + (0.281 (SE = 0.0486) × TG) + (1.65 (SE = 0.394) × CFGR) [n = 83; R2 = 0.46]. In conclusion, the predicted MP requirement for maintenance of Angora goats was 4.30 and 3.35 g/kg BW0.75 with 0 ADG and ) TG and CFGR, respectively, and MP requirements for ADG, TG, and CFGR were 0.318, 0.281, and 1.65 g/g, respectively.


 

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