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Cooperative Extension Service |
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Agricultural
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Aquaculture
Dale Bumpers College
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Beef Cattle Nutrition and Feeding
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| Requirements | |
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Cow's protein requirement |
1.76 lbs (8% DMI) |
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Cow's TDN requirement |
11.44 lbs (52% DMI) |
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Cow's rumen degradable protein requirement |
1.49 lbs (0.13 x TDN) |
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Maximum supply of protein as NPN |
0.45 lbs (0.30 x 1.49) |
| Supplement Supply | |
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Supplement Intake |
1.5 lb per day |
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Crude protein |
40% |
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NPN, CP Equivalent |
19% |
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Supply of NPN from supplement |
0.28 lbs |
CP = crude protein
DMI = dry matter intake
NPN = non-protein nitrogen
TDN = total digestible nutrients
Generally, all natural or true proteins that are high in rumen degradability are preferred for supplements for cows consuming low quality hays (low protein and energy). Urea is a typical non-protein nitrogen source that is used as a protein substitute. This source is broken down by a microbial enzyme (urease) to release ammonia. Microbes incorporate the ammonia into protein by combining it with carbon, and rumen microbiologists say that ammonia is the nitrogen source preferred by cellulolytic bacteria, which are bacteria that feed on forages. This leads to the question, "Why isn’t urea a good source of supplemental protein on low quality forages?" The answer lies within the rate of availability of urea and rate of digestion (or availability of nutrients) from forages that will support and (or) enhance the microbial population.
When urea is fed to cattle consuming low quality forages, there is an imbalance between the rate of ammonia availability and the availability of carbon (from fiber digestion) for the microbes to combine and produce microbial protein. This imbalance leads to the ammonia being absorbed across the rumen wall into the blood stream. Excess ammonia can result in toxicity and high ammonia levels have been linked to reduced pregnancy rates. However, even under conditions that do not pose excesses, ammonia that is not being used by the microbes has the potential to be excreted.
Highly digestible true proteins supply both a readily digestible protein (ammonia source) and supply of carbon (from sugars and proteins) for the microbes to create microbial proteins. Protein supplements that are combined with molasses offers the chance for the ammonia to be used more rapidly because of the rapid solubility of the sugars in the molasses.
Before choosing a protein supplement, be sure protein is needed. If a protein supplement is required, sources of supplements that contain non-protein nitrogen, not exceeding 30% of the cow’s rumen degradable protein requirement, may be an economically feasible alternative to an all natural protein supplement.
Back to Beef Cattle Nutrition and Feeding Frequently Asked Questions
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