Methionine Hydroxy Analog or Sulfate Supplementation for High Producing Dairy Cows

Thirty-six Holstein cows were assigned to three rations. Control rations were supplemented with 25g/day methionine analog or 17.5g/day sodium sulfate. Assignment was by actual or estimated mature equivalent production of the previous lactation. Individual intakes and production were summarized for 18 wk during which rations consisted of 48% concentrate, 42% alfalfa hay cubes, and 10% alfalfa-grass silage. Full lactation records from Dairy Herd Improvement were compared. Average dry matter intake equaled 2.95% of body weight during the feeding-lactation trial. Production averaged 3896kg milk, 3.3% fat, or 4081kg adjusted to 3.5% fat, mature equivalent basis. Production for the full lactation averaged 7480kg milk, 3.3% fat, or 8047kg adjusted. No differences were significant among treatments for feed intake, adjusted production, or percent fat. High producers did not respond differently from lower producers. Analysis of medium and long chain fatty acids of the milk triglyceride fraction did not demonstrate treatment differences. However, there were changes in fatty acid composition between pre-peak samples and milk samples taken as lactation progressed.