Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 7/25/2005
Publication Date: 7/25/2005
Citation: Broderick, G.A., Stevenson, M.J., Patton, R.A., Lobos, N.E., Olmos, J.J. 2005. Supplementing rumen-protected methionine to reduce dietary crude protein in dairy cows [abstract]. Journal of Dairy Science. 88 (suppl 1):89. Interpretive Summary:
Technical Abstract: Over-feeding of crude protein (CP) adds expense and can cause environmental pollution from excess N excretion. Met has been reported to be the amino acid limiting milk and protein yield in dairy cows. Supplementing rumen-protected Met (RPM) may allow feeding less CP without loss of production but with reduced urinary N excretion. A lactation trial was conducted in which dietary CP was reduced in steps of 1.3 percentage units by replacing soybean meal with high moisture shelled corn; RPM (as Mepron®) was increased with each reduction in CP. Twenty-four multiparous Holstein cows averaging 598 kg BW were blocked by DIM into 6 groups and randomly assigned to 4x4 Latin square sequences and fed TMR containing (DM basis): 18.6% CP, 0% Mepron; 17.3% CP, 0.035% Mepron; 16.1% CP, 0.07% Mepron; 14.8% CP, 0.105% Mepron. All diets contained (DM basis) 21% alfalfa silage, 28% corn silage, 4.5% roasted soybeans, 5.8% soyhulls, 0.6% sodium bicarbonate, 0.5% vitamins and minerals, and 27% NDF. Periods were 4-wk long; production data were summarized from the last 2-wk. The statistical model included square, period, cow(square), diet, and diet*period. Probability was set at 0.10; least square means are reported. There were no effects of diet on intake, gain, and yield of protein, lactose and SNF. However, there were significant effects (P Š 0.08) on milk/DM intake and on yield of milk, 3.5% FCM and fat. Production was greater at 17.3% CP plus 8.2 g/d of RPM and 16.1% CP plus 16.6 g/d of RPM, than on the other 2 diets. Apparent N efficiency (milk N/N-intake) was greatest (P < 0.01) on lowest CP diet containing the most RPM. Typical large reductions (P < 0.01) in MUN and estimated urinary N excretion were observed with reduced dietary CP. Under the conditions of this trial, feeding lower CP diets supplemented with RPM resulted in improved N-efficiency and reduced urinary N excretion.