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Multiparous Holstein cows at six universities were utilized to examine effects of ruminally protected methionine and lysine on lactational performance. Three hundred and four cows began the study; 259 cows were included in the production analysis. Following a 21-d standardization period, cows received a basal diet of corn silage and ground corn supplemented with one of five dietary treatments, which were supplements of soybean meal or corn gluten meal, the latter with zero and three combinations of protected methionine and lysine (methionine; methionine and lysine; methionine and double (2x) lysine). Treatment effects were evaluated during early, mid, late, and total lactation (22 to 112, 113 to 224, 225 to 280, and 22 to 280 d postpartum, respectively). On a DM basis, ratios of forage to concentrate (50:50, 60:40, and 70:30) increased, and dietary CP (16.0, 14.5, and 13.0%) decreased during the three periods of lactation. Amount of amino acid supplementation also decreased (15, 12, and 9 g/d methionine; 20, 16, and 12 g/d lysine; and 40, 32, and 24 g/d 2x lysine) with period of lactation. Actual and least squares means for milk, FCM, and milk protein yields were greater for soybean than for corn gluten meal during early, mid, and total lactation. In addition, these variables responded linearly to lysine in early lactation. Response to lysine was quadratic during mid and total lactation for these variables. Differences in nutrient intake explained production responses to protein sources but not to lysine. Serum amino acid responses primarily reflected differences in dietary protein source and rumen-protected amino acid.

In two trials, 47 and 54 Holstein cows were fed diets containing ensiled forages, ensiled and dry forages, or diets of different moisture contents. In trial 1, diets were fed during a preliminary dry period, early lactation, late lactation, a second dry period, and a second early lactation. In trial 2, four diets identical except for moisture content (78, 64, 52, and 40% dry matter) were fed for the first 200 days of lactation. Substitution of dry hay for alfalfa silage increased dry matter intake during the first early lactation, whereas partial substitution of corn silage with straw did not affect intake during dry periods. Dry matter intake increased linearly as dry matter content of diet increased in trial 2. Neither milk production nor body weight were affected by treatment in either trial. Percentage total solids increased linearly as dry matter content of diet decreased in trial 2. Volatile fatty acids differed slightly, but no trends were consistent. No differences of daily chewing time were observed. From these trials, diets of less than 60 to 65% dry matter may reduce intake by lactating dairy cows.

Forty-six Holstein cows (30 primiparous) were assigned to one of four dietary treatments arranged as a 2 x 2 factorial experiment during wk 4 to 17 of lactation. Main effects were corn versus dried sugar beet pulp and soybean meal versus animal by-product meal (mixture of meat and bone meal, feather meal, and blood meal). Beet pulp replaced half of the corn at 15% of dietary DM. Diet DM (mean of four treatments) contained 18% alfalfa pellets, 17.4% alfalfa hay, 17.2% corn silage, and 47.1% concentrate. Milk yield did not differ among treatments (mean 32.0 kg/d). Dry matter intake, milk CP percentage, and milk CP yield decreased 5.6, 3.7 and 5.2%, respectively, but milk fat percentage increased 4.7% when beet pulp replaced corn. Animal by-products did not affect DMI or milk fat, but milk CP percentage decreased 3.0%. The same diets were evaluated in a continuous culture system. Fungal extract (Aspergillus oryzae), added as the third treatment, had little effect on fermentation. Digestion of DM, OM, NDF, and ADF were not affected by dietary treatments. Molar proportion of acetate was greater when corn was replaced by beet pulp. Although flow of NAN from fermenters increased by 3.2% with beet pulp and 3.1% with animal by-products, milk CP percentages decreased.

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