Using the Plasma Dose Response Method to Determine the Bioavailability of Two Commercially Available Rumen-Protected Methionine Products In Lactating Holsteins

Amino acids are fundamental molecules required for protein synthesis, metabolic function, and productivity of dairy cows. Methionine, an essential amino acid that must be provided through the diet, has many biochemical roles relating to cellular metabolism, antioxidation, lactation, and acting as precursors to other compounds. Due to the high demands placed on milk production in the dairy industry and the extensive nutritional requirements involved, rumen-protected methionine supplements have emerged as a strategy to bridge this nutritional gap. In the conducted study, the plasma-dose response method was used to assess the bioavailability of various rumen-protected methionine prototypes in a group of nine lactating, non-cannulated Holstein cows. This technique measures concentrations of specific amino acids as an indicator of absorption and metabolic utilization. Milk, blood, and feed samples were collected on a regular schedule throughout the study to evaluate feed intake, milk output, milk composition, blood amino acid profiles, and total sulfur amino acid concentrations across treatments. Cows were fed individually on a formulated basal diet with assigned treatments. Results revealed that Smartamine, the positive control, and the Milk Specialties prototype had the greatest relative bioavailability across the study group, compared with Kessent M and Prototypes A3-A7. Smartamine and Milk specialties also had the highest concentration of methionine and TSAA compared to the other treatments, supporting the efficacy of their high absorption rates. There were no significant changes in milk composition, except for lactose%. These findings emphasize the importance of targeting methionine supplementation for optimizing milk production and supporting overall dairy cow health through assessing various formulations.