Effect of feeding methionine supplements with different rumen escape values on performance of high producing dairy cows in early lactation

A study was undertaken to compare a liquid form of methionine hydroxy analog (MHA; Novus Intl., Atlanta, GA, USA) and D,L-methionine, two methionine supplements with different rumen degradation escape values, on early lactational and reproductive performance by high producing dairy cows. Forty pregnant Holstein cows housed in a free-stall barn, were blocked by parity, date of calving, and previous 305-day mature equivalent milk production, and at calving were assigned randomly to one of two total mixed rations (TMR) containing MHA, or D,L-methionine, and group-fed for ad libitum intake. Cows spent 33 +/- 15.0 days in the fresh group, after which they were moved to the high producing group where they stayed up to 8-week postpartum. The TMR were formulated to meet approximately 100% of required methionine, lysine, and other essential amino acids. An adequate amount Of D,L-methionine was fed in order to provide a similar amount of methionine postruminally as provided by MHA, assuming a rumen degradation escape value of 40% for MHA and 22% for D,L-methionine. The TMR had forage to concentrate ratio of 40 to 60% for fresh group cows and 42 to 58% for high group cows. There were no differences between treatments in milk yield, content of milk fat, CP and true protein, linear somatic cell count, change in body condition score, and days to first service. In conclusion, D,L-methionine performed as well as MHA in promoting milk yield and contents of milk fat and protein when fed at levels aimed at supplying similar amounts of methionine postruminally as would be supplied by MHA fed at the recommended level. (C) 2003 Elsevier Science B.V. All rights reserved.