Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/16/2010
Publication Date: 4/1/2011
Publication URL: naldc.nal.usda.gov/catalog/53904
Citation: Chen, Z.H., Broderick, G.A., Luchini, N.D., Sloan, B.K., Devillard, E. 2011. Effect of feeding different sources of rumen-protected methionine on milk production and N-utilization in lactating dairy cows. Journal of Dairy Science. 94:1978-1988. Interpretive Summary: Dietary protein supplies lactating cows with amino acids, the building blocks required by the cow to make the protein in milk and body tissues. About half of the amino acids in protein are essential, meaning that they are not made in the body, but must be absorbed from the intestine. Feeding too much protein to dairy cows results in excessive nitrogen excretion in the urine; this form of excretory nitrogen is the most polluting. Supplementation with the limiting essential amino acid is commonly done in non-ruminant nutrition to allow the feeding of lower protein diets that result in reduced urinary nitrogen excretion. This strategy can now be used in dairy cattle because methionine, an essential amino acid that is often limiting on typical rations fed in North America, is commercially available in rumen-protected forms (coated with materials that physically protect the methionine from breakdown by the microbes living in the rumen, thus allowing the amino acid to be absorbed at the intestine when the material is fed in the diet). A new, cheaper form of protected methionine has just become commercially available. We conducted a study to compare the two forms of methionine in lactating dairy cows. Results with either methionine source were similar, indicating that the less expensive chemically protected form is as effective as the physically protected form of methionine. This research indicates that wastage of dietary protein on U.S. dairy farms can be reduced by an inexpensive supplement of rumen-protected methionine. Moreover, this strategy is even more effective for supporting higher yields of protein and fat than feeding more protein. These results mean that U.S. dairy farmers could supplement with rumen-protected methionine to reduce nitrogen pollution of the environment while improving profits.
Technical Abstract: Objectives of this study were to quantify production responses of lactating dairy cows to supplying absorbable Met as isopropyl-2-hydroxy-4-(methylthio)-butanoic acid (HMBi), or rumen-protected Met (RPM, Smartamine® M) fed with or without 2-hydroxy-4-(methylthio)-butanoic acid (HMB), and to determine whether Met supplementation will allow the feeding of reduced dietary CP. Seventy cows were blocked by parity and DIM into 14 blocks and randomly assigned within blocks to 1 of the 5 dietary treatments based on alfalfa and corn silages plus high moisture corn: 1 diet with 15.6% CP and no Met source (negative control); 3 diets with 15.6 % CP plus 0.17% HMBi, 0.06% RPM (as Smartamine® M) + 0.10% HMB, or 0.06% RPM alone; and 1 diet with 16.8% CP and no Met supplement (positive control). Assuming 50% of ingested HMBi was absorbed from the gastrointestinal tract and 80% of the Met in RPM was absorbed at intestine, the HMBi and RPM supplements increased metabolizable Met supply by 9 g/d and improved Lys: Met ratio from 3.6 to 3.0. After a 2-wk covariate period during which all cows received the same diet, cows were fed test diets continuously for 12 wk. Diet did not affect (P = 0.43) DM intake (mean ± SD 25.0 ±0.3 kg/d), BW gain (0.59 ± 0.2 kg/d) or milk yield (41.7 ± 0.6 kg/d). However, feeding HMBi increased (P = 0.02) yield of energy corrected milk (ECM) and milk content of protein and SNF. Moreover, there were trends for increased milk fat content and yield of fat and true protein on all 3 diets containing supplemental Met. Feeding 16.8% CP without a Met source elevated MUN, urinary excretion of urea-N and total-N, and reduced apparent N efficiency (Milk N/N intake) from 34.5 to 30.2%, without improving production. Results with the different Met sources were similar, indicating that feeding HMBi will improve milk production and N utilization to the same extent as RPM.