Date of Award

Spring 2005

Project Type

Dissertation

Program or Major

Animal and Nutritional Sciences

Degree Name

Doctor of Philosophy

First Advisor

Charles G Schwab

Abstract

The most effective method for increasing supplies of MP-Met to dairy cows to increase milk protein production is to feed rumen-protected Met ( RP-Met) products; however, not all RP-Met products are absorbed by the dairy cow in the same manner. Universally acceptable methods must be developed to determine the efficacy of different RP-Met products.

The first study was designed to compare the feeding of two sources of supplementary Met beginning 21 d prepartum and continuing for 140 d postpartum. The results indicated that feeding both sources of RPMet to periparturient dairy cows is effective in increasing milk protein production; however, clarification of their relative contributions to metabolizable Met is still needed.

The second study was designed to compare the effects of providing supplemental RP-Met in the form of Met analogs (MetaSmart) or DL-Met (Smartamine M) to lactating dairy cows fed Met-deficient or Met-adequate diets on plasma sulfur AA and milk protein concentrations. Results demonstrated that using changes in milk protein determine the amount of absorbable Met provided by MetaSmart relative to that of Smartamine M is not as precise as using changes in plasma sulfur AA concentrations. This study also demonstrated that Met analogs are metabolized differently than DL-Met sources and that more research is needed to determine the best response criteria for determining the efficacy of Met analogs.

The third study was designed to determine the benefit of increasing MP-Met and MP-Lys concentrations on increasing milk and milk protein yields. Published studies in the Journal of Dairy Science were entered into the NRC (2001) model to generate predicted flows of MP, MP-Met, and MP-Lys (g/d). Plots were developed by regressing measured milk and milk protein yields on predicted supplies of MP, MP-Met, and MP-Lys (g/d). Results indicated that prediction equations based on NRC (2001) predicted flows of the first or co-limiting AA may be more accurate at predicting milk and milk protein yield than MP flows and predicting milk protein yield from flows of MP, Met and Lys is more accurate than predicting milk yield.

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