Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract only
Publication Acceptance Date: 4/23/2010
Publication Date: 7/12/2010
Citation: Broderick, G.A., Patton, R.A., Heimbeck, W., Parys, C. 2010. Effect of feeding varied levels of crude protein and absorbable methionine on milk yield in lactating dairy cows. Journal of Dairy Science. 93(E-Supplement 1):444. Interpretive Summary:
Technical Abstract: Supplementing with limiting AA should allow less CP to be fed; reducing dietary CP will decrease urinary N and ameliorate the environmental impact of dairying. Rumen-protected Met (RPM), fed as Mepron to provide 9 g/d of absorbable Met, allowed similar milk yield at 15.8% CP as at 17.1% CP without RPM (Broderick et al., J. Dairy Sci. 92:2719, 2009). A lactation trial was conducted to assess response to RPM at different CP levels. TMR were prepared from alfalfa and corn silages, dry- and high-moisture corn, and solvent and expeller soybean meals. Diets were formulated to 28% NDF and 12, 14, 16 or 18% CP (DM basis); at each level of CP, RPM provided 0, 4.5, 9.0 and 13.5 g/d of absorbable Met, assuming 25 kg/d of DMI and 0.6 g absorbed Met/g of Mepron (total = 16 diets). Sixty-four cows were blocked by DIM into 16 squares and randomly assigned to balanced 4x4 Latin squares. The 4 levels of RPM were fed at each CP level for four 4-wk periods. Data from the last 2 wk of each period were analyzed for linearity of response to dietary CP and RPM using the mixed model of SAS; LS means were reported. Analysis of TMR extracts with the Met-nitroprusside reaction confirmed that RPM was fed in desired amounts, but CP was higher than formulated. Dietary CP increased DMI, BW gain, and yield of milk, 3.5% FCM, fat and protein, but did not affect milk/DMI. Production was not increased when diets contained 15.8% or more CP. Although the NRC model indicated that diets had Lys/Met ratios ranging from 3.3 to 3.7, and observed milk yield was more than MP-allowable milk on 12.9 and 15.8% CP, more absorbable Met had no effect on production in this trial.