Extent of methionine limitation in peak-, early-, and mid-lactation dairy cows.
Five multiparous, ruminally and duodenally cannulated Holstein cows were assigned to 5 x 5 Latin squares at wk 2 (experiment 1), wk 11 to 13 (experiment 2), and wk 17 to 19 postpartum (experiment 3) to determine extent of Met limitation. Treatments were duodenally infused and consisted of 10 g/d of l-Lys plus 0, 3.5, 7.0, 10.5, or 16.0 g/d of dl-Met in experiments 1 and 2 and 8 g/d of l-Lys plus 0, 5, 10, 15, or 20 g/d of dl-Met in experiment 3. Calculated Lys contributions to total AA (TAA) in duodenal digesta for control treatments were 8.6, 7.5, and 9.0% for experiments 1, 2, and 3, respectively. Methionine contributions to TAA for the 5 infusion treatments were 1.9, 2.1, 2.2, 2.4, and 2.7% for experiment 1; 2.1, 2.3, 2.4, 2.5, and 2.7% for experiment 2; and 1.8, 2.0, 2.2, 2.4, and 2.5% for experiment 3, respectively. Milk protein yield increased linearly in experiments 1 and 2, indicating that Met contribution to TAA in duodenal digesta for maximal milk protein synthesis exceeded 2.7 for early-lactation cows. In experiment 2, a quadratic relationship was found between level of infused Met and milk protein content, with the response reaching a plateau when 12.2 g of Met was infused, corresponding with a Met contribution to TAA in duodenal digesta of 2.4%. In experiment 3, milk protein content increased quadratically, but milk yield declined linearly with increasing levels of infused Met; hence, milk protein yield was unaffected by treatment. The calculated plateau point of the milk protein content response curve was determined to be 12.4 g of infused Met, which corresponds to a Met contribution to TAA in duodenal digesta of 2.3%. Experiment 3 results indicate that the required level of Met in duodenal digesta for maximizing milk protein yield is lower than that required for maximizing milk protein content.
Socha
M T
MT
Zinpro Corporation, Eden Prairie, MN 55374, USA. msocha@zinpro.com
Schwab
C G
CG
Putnam
D E
DE
Whitehouse
N L
NL
Garthwaite
B D
BD
Ducharme
G A
GA
D000596:Amino Acids / Q000032:analysis; D000821:Animal Feed / Q000032:analysis; D000818:Animals; D001806:Blood Urea Nitrogen; D002417:Cattle / Q000502:physiology*; D004032:Diet; D004063:Digestion; D004386:Duodenum / Q000737:chemistry; D004435:Eating / Q000502:physiology; D005223:Fats / Q000032:analysis; D005260:Female; D006863:Hydrogen-Ion Concentration; D007774:Lactation / Q000502:physiology*; D008715:Methionine / Q000008:administration & dosage* / Q000032:analysis / Q000172:deficiency; D008892:Milk / Q000737:chemistry; D008894:Milk Proteins / Q000032:analysis; D009751:Nutritional Requirements; D012417:Rumen / Q000737:chemistry
D000596:Amino Acids; D005223:Fats; D008894:Milk Proteins; D008715:Methionine