Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Dairy Science

First Advisor

Joel L. Sommerfeldt


The high producing dairy cow requires a complex balance of protein and energy. Microbial protein provides a substantial amount of the amino acids absorbed by the small intestine. High production rates cannot be attained with microbial protein as .the sole source of amino acids. The ten classical essential amino acids are required for milk protein synthesis. Increasing the amount of available amino acids to the mammary gland has improved casein production, indicating substrate availability as a controlling factor to milk protein synthesis. A major portion of the nitrogen component of milk is derived from free plasma amino acids. Uptake by the mammary gland is a key to milk protein production. Amino acid absorption is a process of active diffusion and is dependent upon: arterial concentration of amino acids, rate of mammary blood flow, and the extraction process by the alveolus of the mammary gland. Protein and amino acid research has concentrated on determining the amino acid or amino acids most limiting to milk production and the most appropriate means of presenting these nutrients to the small intestine for absorption. Microbial degradation accounts for a high rate of nitrogen turnover in the rumen. The amino acid profile of feedstuffs reaching the small intestine are not in the same proportion as those in the diet. To change the status of the amino acid profile reaching the small intestine, protection of dietary proteins and amino acids has become an area of concentrated research. Heat treatment, chemical treatment and encapsulation have been utilized as protection devices. The amino acid most frequently found limiting to milk production is methionine. Lysine, phenylalanine, and threonine have also been implicated as limiting or co-limiting. Feeding of protected sources of proteins or amino acids has shown variable results. Abomasal infusions of amino acids and casein have exhibited increases in milk production and milk protein production. The objective of this research was to feed rumen-protected methionine in a diet likely limited in methionine and measure milk production responses to the supplementation.

Library of Congress Subject Headings

Dairy cattle -- Feeding and feeds
Amino acids in animal nutrition
Milk yield


Includes bibliographies



Number of Pages



South Dakota State University


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Included in

Dairy Science Commons