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; Adisseo, Alpharetta, GA) fed with or without 2-hydroxy-4-(methylthio)-butanoic acid (HMB), and to determine whether Met supplementation will allow the feeding of reduced dietary crude protein (CP). Seventy cows were blocked by parity and days in milk 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 + 0.10% HMB, or 0.06% RPM alone; and 1 diet with 16.8% CP and no Met supplement (positive control). Assuming that 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 the 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 dry matter intake (mean ± SD, 25.0±0.3 kg/d), body weight gain (0.59±0.2 kg/d), or milk yield (41.7±0.6 kg/d). However, feeding HMBi increased yield of energy-corrected milk and milk content of protein and solids-not-fat. Moreover, trends were observed for increased milk fat content and yield of fat and true protein on all 3 diets containing supplemental Met. Apparent N efficiency (milk N/N intake) was highest on the RPM treatment. Feeding 16.8% CP without a Met source elevated milk urea N and urinary excretion of urea N and total N and reduced apparent N efficiency from 34.5 to 30.2%, without improving production. Overall results suggested that feeding HMBi or RPM would give similar improvements in milk production and N utilization.

Eighteen primiparous and 42 multiparous Holstein cows were blocked according to parity and expected calving date and assigned randomly to 1 of 3 dietary treatments: 1) a basal diet (negative control), 2) the basal diet plus 2-hydroxy-4-methylthio butanoic acid isopropyl ester (MetaSmart, Adisseo Inc., Antony, France), or 3) the basal diet plus rumen-protected Met (Smartamine M, Adisseo Inc., Alpharetta, GA). Treatments were initiated 21 d before expected calving and continued through 140 d postpartum. Diets were similar in ingredient and chemical composition, except for the content of Met in metabolizable protein. MetaSmart [0.35% prepartum and 0.54% postpartum in diet dry matter (DM)] and Smartamine M (0.06% prepartum and 0.10% postpartum in diet DM) were added to the basal diet in amounts needed to achieve a 3.0:1 ratio of Lys to Met in metabolizable protein. Prepartum DM intake (DMI; 13.5 kg/d), body weight (687 kg), body condition score (3.81), postpartum milk yield (42.0 kg/d), milk fat yield (1,549 g/d), milk fat content (3.66%), milk true protein yield (1,192 g/d), and milk urea N content (12.9 mg/dL) were not different among treatments. Postpartum DMI and body condition score were greater and the ratios of milk:DMI and milk N:feed N were less for cows fed the MetaSmart diet than for cows fed the control and Smartamine M diets. Milk protein content was greater for the Smartamine M (2.87%) and MetaSmart (2.81%) treatments than for the control treatment (2.72%). Concentrations of Met and Met + Cys in total plasma AA were different among treatments, with values for the Smartamine M treatment being the highest, followed by the MetaSmart and control treatments. The results indicated that both MetaSmart and Smartamine M are effective in providing metabolizable Met, but clarification of their relative contributions to metabolizable Met is still needed.

Interactions between supplementation with ruminally protected Met and Lys and the nature of protein or energy concentration of the diet were studied using 16 and 12 multiparous lactating dairy cows in two trials of 8 and 12 wk, respectively, commencing on approximately d 40 of lactation. In trial 1, cows received a semicomplete diet plus concentrates. The diet consisted of 62 to 63% corn silage, 2.2% corn gluten meal, .4% urea, 11% soybean meal (untreated or treated with formaldehyde), and 23 to 24% barley. In trial 2, cows received a complete diet with corn silage, untreated and formaldehyde-treated soybean meal, and barley in the ratio 78:12:9:0 or 49:13:4:33. All treatments were replicated in a 4 x 4 Latin square design. In both trials, Met plus Lys (10 g/d of intestinally available Met and 30 g/d of Lys) has no significant effect on DMI, milk yield, fat content, casein as a percentage of true protein, or urea content of the milk. Mean increase of milk protein yield was 46 g/d with Met plus Lys, and mean increase of true protein content was 1.1 g/kg of milk. The increase in content of milk true protein was greater for cows receiving the low energy diet. Protein source had no effect on milk yield or composition. Glucose, urea, NEFA, BHBA, and total free AA in plasma were unaffected by supplementation of ruminally protected Met plus Lys. However, concentrations of Met and Lys in blood were slightly, but not significantly, higher in supplemented cows.

There is increasing interest in how the raw material make-up of concentrates can influence the milk performance of dairy cows. Thus, over two consecutive winters, 54 dairy cows were used to investigate the effects on dry matter (DM) intake, milk yield and its composition of feeding concentrates of diverse energy source (LNDF — 131 g neutral-detergent fibre per kg DM, 492 g starch plus sugars per kg DM; HNDF — 244 g neutral-detergent fibre per kg DM, 293 g starch plus sugar per kg DM) at two formulated crude protein (CP) levels (157v.187 g/kg DM) and three levels of concentrate allowance (9, 11, 13 kg DM). The concentrates were formulated to be of equivalent metabolizable energy concentration (MJ/kg DM) and were offered with silagead libitumfor a 10-week period (weeks 4 to 13 of lactation).Silage intakes were variable but not significantly influenced by concentrate energy source or formulated CP level, except in the 1st year where animals consuming the high CP concentrate ate more silage. Silage DM intake decreased as concentrate allowance was increased with the substitution rate (kg silage DM per kg concentrate DM) increasing as concentrate allowance was increased.Increasing the concentrate allowance effected the expected increases in milk yield. Concentrate energy source did not influence milk yield but the higher CP levels effected a 2-kg increase in milk yield. Feeding of LNDF concentrates depressed milk fat concentration and its yield, the depression being accentuated with each increase in concentrate allowance. The depression in milk fat concentration was negatively correlated with the forage: concentrate ratio of the diet consumed. Furthermore, dietary NDF proportion was shown to account for greater than half of the variation in milk fat concentration. In contrast to the observations made for milk fat, feeding the LNDF concentrates effected an increase in milk protein concentration but only at the lower CP level of the concentrate.

Methionine and lysine have been shown to be the two amino acids most limiting for milk protein synthesis in lactating dairy cows. Many studies have shown positive effects of adding protected forms of methionine to cows on maize silage-based diets supplemented with soyabean meal. The aim of this study was to evaluate the effect on milk production and composition of adding protected methionine and lysine to cows fed a grass silage diet.24 Autumn-calved cows (2nd lactation or greater) were blocked into groups of 4 based on calving date and milk yield in the immediate pre-experimental week. Cows within each group were subjected to each of the following 4 treatments in a latin square design: (1) 7 kg of by-product concentrate per day (C), (2) C plus 4.8 g digestible methionine per day (3) C plus 4.8 g digestible methionine and 6.2 g digestible lysine per day (4) 7 kg of barley-soya concentrate + 7.7 g digestible methionine per day. Each period lasted 4 weeks and data from weeks 3 and 4 were used to compare treatment effects. The amino acids were supplied in a rumen protected form (SmartamineTM, RPAN Technology) and all figures relate to estimated intestinally digestible amino acids based on the French system of calculating digestible lysine and methionine. The cows received primary growth unwilted grass silage ad libitum (Oven Dry Matter 189 g/kg, in-vitro DMD 714 g/kg DM, Crude protein 160 g/kg DM, pH 3.9).