Date of Award

Winter 1994

Project Type

Dissertation

Program or Major

Animal and Nutritional Sciences

Degree Name

Doctor of Philosophy

First Advisor

Charles G Schwab

Abstract

Five, multiparous, Holstein cows fitted with ruminal and duodenal cannulas were assigned to 5 x 5 Latin squares at peak, early, and mid lactation to determine the required level of Met in duodenal digesta for maximum synthesis of milk protein. Cows were fed corn-based diets, formulated to be most limiting in Met and Lys, and were infused with incremental amounts of Met and a basal amount of Lys. The calculated required contributions of Met to total essential AA passing to the duodenum for maximum milk protein synthesis exceeded 5.5 and 5.2% of essential AA for the peak and early lactation cows, and was less than 5.0% of essential AA for the mid lactation cows.

In the second study, four, early lactation, multiparous, Holstein cows fitted with ruminal and duodenal cannulas were assigned to an incomplete, 5 x 5 Latin square to determine the effect of supplementing Met when Lys appeared to be the first limiting AA. Cows were fed a corn-based diet that appeared most limiting in Lys, and treatments were daily infusions into the duodenum of 0, 5, 10, or 15 g/d of DL-Met, or 10 g/d of DL-Met plus 20 g/d of L-Lys. Milk protein yield was lower for the Met only treatments in comparison to the Lys plus Met treatment. There was no effect of treatment on milk composition or yield of milk, energy-corrected milk, or FCM.

In the third study, eighty, multiparous, Holstein cows were assigned to randomized, incomplete block, experiment to determine the lactational responses to Met and Lys supplementation. Treatments were either a 16 or 18.5% CP diet supplemented with: (1) no rumen-stable AA, (2) 10.5 g/d of Met from rumen-stable Met, (3) 10.2 g/d of Met and 16 g/d of Lys from a rumen-stable Lys plus Met product. There was no response to Met alone. However, cows receiving both Lys and Met produced more milk protein and energy-corrected milk and tended to produce more milk and FCM. Responses to Lys and Met supplementation were greatest in the first eleven weeks of lactation, and largest for cows consuming the 18.5% CP diet.

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