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Citation of this paper

Rumen escape protein

T R Preston and R A Leng1

Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV)
Carrera 25 No 6-62 Cali, Colombia
1 University of New England, Armidale, NSW, Australia

In 1963, Whitelaw and Preston identified the role of solubility and amino acid balance as determinants of the nutritive value of proteins for efficient growth, reproduction, and milk yield in ruminants.

When this concept was applied in cattle fattening systems in Cuba in the 1960-70's the term "bypass protein" was used to identify sources of protein that had these characteristics of low solubility and high biological value in terms of the balance of amino acids, The term was used in the Book "Matching Ruminant Production Systems with Available Resources in the Tropics and Sub-Tropics" published in 1987 and in our position paper published earlier this year (Preston et al 2021).

At the time this nomenclature was convenient but was inaccurate and confusing as the implication of the word "bypass" is that dietary protein "avoided" the rumen passing directly to the abomasum and small intestine, which clearly is incorrect. The protein enters the rumen when feed is consumed and thereafter, depending on its solubility and attachment to other substances such as tannins, some of that protein will escape from fermentative processes increasing the total amino acid supply (from dietary sources and microbial cells) for more efficient digestion by mammalian enzymes in the small intestine.

We, therefore, propose to refine the nomenclature for identifying protein sources that are of low solubility and that it is this characteristic that facilitates the partial escape of the protein from the rumen fermentation. We propose to use the term "rumen escape protein" because this is a more accurate definition of what actually happens.


Preston T R and Leng R A 1987 Matching Ruminant Production Systems with Available Resources in the Tropics and Sub-Tropics.

Preston T R, Leng R A, Phanthavong V and Gomez M E 2021 Fattening cattle with tropical feed resources; the critical role of bypass protein. Livestock Research for Rural Development. Volume 33, Article #86.

Whitelaw F G and Preston T R 1963 The nutrition of the early-weaned calf III. Protein solubility and amino acid composition as factors affecting protein utilization. Animal Production / Volume 5 / Issue 02 / June 1963, pp 131 - 145 DOI: 10.1017/S0003356100021620, Published online: 02 September 2010.