Protected Methionine Supplementation with Extruded Blend of Soybeans and Soybean Meal for Dairy Cows

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Abstract
Methionine may be the first amino acid limiting milk production in early lactation cows. To evaluate this further, 23 high producing Holstein cows (9 multiparous and 14 primiparous) were fed an extruded blend of soybeans and soybean meal (40:60) without or with 15 g of added DL-methionine as 50 g of ruminally protected methionine product during wk 4 to 16 postpartum. Cows were fed a 15.8% crude protein total mixed ration consisting of 30% (dry basis) corn silage, 15% alfalfa hay, and 55% concentrate mix. Covariant-adjusted yields of milk (35.3 and 33.9 kg/d) and solids-corrected milk (29.3 and 28.2 kg/d) were lower for cows fed ruminally protected methionine, whereas yields of 4% fat-corrected milk (28.2 and 27.4 kg/d) were similar. Percentages of fat (2.68 and 2.69) and solids-not-fat (8.82 and 8.83) were similar, and percentages of protein (2.86 and 2.90) were higher from cows fed supplemental methionine. Dry matter intakes (20.5 and 21.6 kg/d) were higher for cows fed ruminally protected methionine. Methionine concentrations in arterial and venous serum were elevated slightly by feeding supplemental methionine. Although methionine was still the first-limiting amino acid as calculated by two different methods, supplementation of this diet with ruminally protected methionine did not increase production of early lactation cows.