We evaluated the influence on milk production of feeding early lactation cows a diet that included 14.5% crude protein (CP) and that did not meet methionine (Met) requirements or that met them by supplying rumen‐protected Met (RPMet). Thirty‐nine multiparous Holstein cows were allocated into two groups. For 15 weeks after calving, each group was fed one of the two total mixed rations, Control ( n = 20) or Treatment ( n = 19). The Treatment group received added RPMet at 0.034% (8 g/day) of the Control diet on dry matter basis. The adequacies of Met for the Control and Treatment groups were 96% and 106%, respectively, and for other amino acids, >110%. The CP level (14.5%) was 1 percentage point lower than that recommended by the Japanese Feeding Standard (2006). No between‐group differences were found in milk yield (40 kg/day), milk composition, plasma profile, rumen fermentation, nitrogen balance, or cow health. Met intake and the amount of rumen‐undegradable feed Met were higher in the Treatment group ( p < 0.05). Microbial Met and total metabolizable Met did not differ between groups. Supplying RPMet in a 14.5% CP diet during early lactation did not dramatically affect milk production, because the amount of total metabolizable Met was unchanged.

Table 1.Ingredient and nutrient composition of Low by-product (LB), Medium by-product (MB), High by-product (HB) diets 1) Trace minerals (contained 0.44% Fe, 0.35% Cu, 0.46% Zn, 0.33% Mn, 0.005% Co, 0.13% Mg, 0.04% I) and vitamin A, D, E (contained 2,816IU/g vitamin A, 264 mixture.2) NFC=100-(CP+EE+NDF+Ash). Levels of rolled maize, soybean meal and wheat bran in early lactating dairy cows diets were partially replaced by tofu cake, brewers grain and full-fat rice bran, and their effects were studied. Sixty-eight multiparous Holstein cows were used in an experiment in a randomized block design to investigate the effects of the diets on ruminal fermentation characteristics, digestion, plasma composition and milk production. Three diets LB (low), MB (medium) and HB (high) were prepared using different levels of by-products. The cows were divided into three groups, A (n=24), B (22) and C (22), and each group was fed one of three treatment diets as total mixed rations for 15 weeks after calving.Results showed that the by-products level did not affect the dry matter intake of cows. Increasing by-products level in diet increased gross energy content but decreased total tract apparent energy digestibility of the diet. Therefore, by-products level did not affect the digestible energy intake. Milk yield was lower (P<0.05) for HB than LB diet (36.6 vs 40.8kg/d).Milk fat % was higher (P<0.05) for HB or MB than LB diet. However, production of 4% fat-corrected milk tended (P<0.10) to be higher for LB than HB diet (38.0 vs 35.5kg/d). These results suggested that replacement of rolled maize, soybean meal and wheat bran with tofu cake, brewers grain and full-fat rice bran should be kept less than 10% of the total diet.

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