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Lactational performance of dairy cows supplemented with N-acetyl-l-methionine.

S. E. Räisänen



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Lactational performance of dairy cows supplemented with N-acetyl-l-methionine.
S. E. Räisänen, X. Zhu, C. F. A. Lage, M. E. Fetter, H. A. Stefenoni, A. Melgar, D. E. Wasson, S. F. Welchez, J. S. Eun, J. Park, A. N. Hristov. The Pennsylvania State University University Park, PA, Institute of Subtropical Agriculture, Chinese Academy of Sciences Changsha, Hunan, China, 3University of Chinese Academy of Sciences Beijing, China, 4Institute of Biotechnology, CJ Blossom Park Suwon, Korea.

The objective of this experiment was to determine the effect of N-acetyl-l-methionine (NALM) on milk production and milk composition in lactating dairy cows fed a diet that meets or exceeds the requirements for energy and metabolizable protein (MP) but is deficient in digestible Met (dMet), according to NRC (2001). Eighteen multiparous Holstein cows [60 � 1.5 d in milk, 638 � 15 kg BW, 52.8 � 2.98 kg milk yield (MY)] were used in a replicated 3 � 3 Latin square design experiment with three 28-d periods, balanced for residual effects. Treatments were (1) basal diet supplying 1.66% digestible (d)Met (CON), (2) basal diet supplemented with 32 g/d NALM (NLow), (3) basal diet supplemented with 56 g/d NALM (NHigh). The NALM treatments supplied estimated 16.7 and 29 g/d dMet, respectively. The NALM was top-dressed on the basal diet at morning feeding. Dry matter intake (DMI) and MY were recorded daily, and milk sampling was performed on the last week of each experimental period from 4 consecutive milkings (2, AM and 2, PM). Data were analyzed using PROC MIXED of SAS with treatment and period in the model. Square and cow within square were random effects. Linear effects of NALM dose were tested. Dry matter intake was similar (P = 0.76) among treatments (averaging 24.7 kg/d; SEM = 0.72). Milk yield was also not affected (P = 0.64) by treatment (averaging 50.7 kg/d; SEM = 1.56), whereas ECM was decreased linearly (P = 0.03) by NALM (48.1, 45.1 and 45.0 kg/d, respectively) as a result of a linear decrease (P = 0.004) in milk fat concentration (3.77, 3.47, 3.33%, CON, NLow, and NHigh, respectively). Similarly, there was a linear decrease (P = 0.007) in milk fat yield with increasing NALM dose: 1.92, 1.74, and 1.69 kg/d for CON, NLow, and NHigh, respectively. The concentration and yield of both lactose and milk true protein were not affected by treatment (P > 0.10). In the conditions of this experiment, supplementing NALM to an MP-adequate diet supplying dMet at 1.66% of MP caused a decrease in milk fat and ECM yield and did not affect milk or milk true protein yields in mid-lactation dairy cows.

Keywords: N-acetyl-l-methionine, milk production, dairy cattle.