Author(s): Mullins CR, Weber D, Block E, Smith JF, Brouk MJ,
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Abstract Primiparous (n=33) and multiparous (n=63) lactating Holstein cows (186±51 d in milk) were used to evaluate the effects of supplementing metabolizable amino acids using lysine in a matrix of Ca salts of fatty acids (Megamine-L, Arm & Hammer Animal Nutrition, Princeton, NJ) and the isopropyl ester of 2-hydroxy-4-(methylthio) butanoic acid (MetaSmart, Adisseo Inc., Antony, France) in diets containing >26\% wet corn gluten feed (dry matter basis). Cows were blocked by production level, parity, and pregnancy status, then randomly assigned to 1 of 8 pens and allowed a 7-d adaption period before receiving dietary treatments for 28 d. Pens were assigned randomly to either of 2 diets formulated to differ by metabolizable amino acid supply. Dry matter intake and production were monitored daily and milk components analyzed 3d/wk. Data were analyzed using mixed models with repeated measures. The original design of the study consisted of a control diet predicted to be deficient in lysine and methionine; however, after ingredient nutrients were analyzed and modeled with animal requirements at dry matter intake [26.6±0.35 kg/d (mean ± SEM)] and milk production levels achieved during the study (40.1±0.46 kg/d), only marginal deficiencies were predicted for the control (-8.1g/d for lysine; -1g/d for methionine) according to the National Research Council method, whereas the Cornell Net Carbohydrate and Protein System 5.0 and 6.1 models indicated positive balances for these amino acids (25.9 and 21.8 g/d for lysine, 14.7 and 18.9 g/d for methionine, respectively). Supplementing 30 g/d of metabolizable lysine in a Ca soap matrix and 2.4 g/d of metabolizable methionine as 2-hydroxy-4-(methylthio) butanoic acid led to positive predicted lysine and methionine balances by all 3 models, and predicted metabolizable lysine-to-methionine ratios ranging from 2.9 to 3.1. No treatment effects were observed for dry matter intake, milk yield, milk component concentrations or yields, or energy-corrected milk yield. Despite the negative lysine balance and low lysine-to-methionine ratio predicted by the National Research Council model, results provided no evidence of a lysine deficiency in the control diet. Copyright © 2013 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.
This article was published in J Dairy Sci
and referenced in Journal of Osteoporosis and Physical Activity