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. Effect of supplementing rumen-protected methionine at two levels of dietary crude protein in lactating dairy cows [abstract]. Journal of Dairy Science. 88 (suppl. 1):319. Interpretive Summary:
Technical Abstract: Leonardi et al. (J. Dairy Sci. 86:4033, 2003) reported that supplementing rumen-protected Met (RPM) increased milk protein concentration at both 16.1 and 18.8% crude protein (CP), with no interaction. This would be unexpected if Met were the first-limiting metabolizable AA. Cows in their study were calculated to be in positive energy balance. A 4x4 Latin square lactation trial was conducted with a 2x2 arrangement of diets: 17.3 or 16.1% CP, with or without supplementation of about 15 g/d of RPM (as Mepron®). Diets were fed as TMR and 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. Dietary CP was lowered by replacing solvent soybean meal with high moisture shelled corn. Thirty-two multiparous Holstein cows averaging 604 kg BW were blocked by DIM into 8 groups and randomly assigned to the 4x4 Latin square sequences. Periods were 4-wk long and production data were collected from the last 2-wk. The statistical model included square, period, cow(square), CP, RPM, and CP*RPM; least square means are reported. All treatments were calculated to be in negative energy balance due to lower than expected DMI. There were no effects of RPM supplementation on any production trait. However, higher CP increased (P Š 0.03) yield of milk, protein, and SNF by 1.0, 0.04, and 0.11 kg/d; there were trends (P Š 0.09) for increased DM intake and lactose yield at higher CP. A trend (P = 0.08) for an interaction suggested that protein yield increased when RPM was fed at higher CP but decreased when RPM was fed at lower CP. However, apparent N efficiency (milk N/N-intake) was greater (P < 0.01), and MUN lower (P < 0.01), on lower CP diets and both were unaffected by RPM feeding. Under the conditions of this trial, reducing dietary CP from 17.3 to 16.1% reduced yield of milk, protein and SNF and this reduction was not reversed by supplementing with RPM.