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Protein Digestion

This is an overview of how protein sources are broken down in ruminants and how the protein building blocks are utilized. This is a very scientific blog post but I am hoping to help producers understand why they are feeding the products they are feeding. It is important to understand the basics of how cattle digest feed and how they utilize these nutrients in the body. Please contact me if you would like to discuss any of the information in this blog post.


Ruminants use microbes (bacteria and protozoa) to digest feed to create free amino acids. These amino acids are used by the microbes in the rumen to synthesize microbial protein. Non-protein nitrogen sources include urea, ammonia, free amino acids, small peptides (2 or more amino acids bonded together), and nitrates. These types of protein come from the fermentation of forages or from direct supplementation of urea. These NPN sources are all converted to ammonia which is a major substrate for microbial synthesis. Microbes need energy to synthesize protein, therefore if limited energy, the ability to sequester ammonia is reduced. This will result in ammonia flowing out of the rumen into the bloodstream, the liver will extract this ammonia from the bloodstream and excrete it in urine or recycle it back to the rumen to be used when protein is not being produced from digestion. It is very important to match carbohydrate and protein availability in the diet, this will allow the microbes in the rumen to properly function and utilize all nutrients.


As the feed is digested in the rumen, microbes bond to feed particles to break down the NPN into amino acids which are then absorbed into the cell. These amino acids can be directly converted into microbial proteins. These feed bonded microbes then move through the other chambers of the stomach and are degraded in the abomasum and small intestine where amino acids are absorbed. These absorbed proteins are then transported through the blood to muscles and other parts of the body to promote growth and in some cases, lactation.


Hopefully, this explains the basics of how proteins are digested and utilized in ruminants. I am hoping to get a blog post done on carbohydrate digestion in the next week as well. Carbohydrates are the energy source for the animal. Please let me know any questions you may have.

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