Cattle nutrition: Part Four…protein in cattle diets


PROTEIN supplements in cattle feed, especially beef cattle, often account for a large proportion of supplemental feed costs, including in Zimbabwe.
Feed costs account for a large proportion of cash costs in beef cattle operations. 
Protein is a critical nutrient in all cattle diets. Although protein supplements are often a high cost item in cattle feeding programmes, protein supplementation is needed to meet the animal’s nutrient requirements. Young, growing cattle and lactating cows are most likely to require protein supplement.
Some obvious signs of protein deficiency in cattle include loss of appetite, weight loss, poor growth, depressed reproductive performance and reduced milk production. 
Protein in cattle diets is commonly expressed as crude protein which is comprised of both true protein and non-protein nitrogen (NPN); though not all nitrogen-containing compounds are true proteins. Urea is an example of an NPN source.
Many NPN compounds can supply nitrogen to the rumen microbes that then build microbial protein in the rumen, using this nitrogen. 
To determine the crude protein content of a forage or feedstuff, first measure the nitrogen content of the feed.
Insufficient protein can be a problem on warm-season grasses receiving inadequate nitrogen fertilisation, particularly when forage is allowed to become mature before harvest or when frosted pasture is grazed during winter.
Excessive rainfall can also leach nitrogen from the soil and reduce nitrogen levels available for plant protein production and animal consumption. 
True protein is sometimes also called ‘natural protein’.
It is either degradable (can be broken down) or undegradable (cannot be broken down) in the rumen. Ruminally degradable protein (RDP) is broken down in the rumen and is also referred to as degradable intake protein (DIP).
Ruminally undegradable protein is protein that is not broken down in the rumen but is potentially degradable in the small intestines; sometimes called undegradable intake protein or rumen bypass protein.
A minimum amount of degradable intake protein is needed in the diet to support microbial growth.
Metabolisable protein accounts for rumen degradation of protein. It separates protein requirements into the needs of rumen micro-organisms and the animal’s needs.
Metabolisable protein is true protein absorbed by the intestine.
Cattle diets in rural Zimbabwe are primarily forage based. The protein composition of forages typically varies by forage species, soil nutrients, and forage maturity.
Cool-season forages tend to contain higher crude protein levels than warm-season forages. Crude protein concentration also generally decreases with increasing forage maturity and decreasing nitrogen fertiliser rates.
Cattle protein requirements vary with each stage of production; size of the animal and expected performance.
During lactation, larger cattle typically require greater amounts of crude protein daily than smaller cattle, but as a lesser percentage of their total dry matter intake.
For example; lighter cattle require higher quality feeds and forages at lesser quantities compared to heavier cattle.
Cattle requirements for crude protein increase with increasing lactation and rate of gain. Protein is required for milk production and reproductive tract reconditioning after calving.
High-protein feeds are best used when forage availability is abundant. Average daily gains in nursing calves tend to increase with increasing crude protein content of creep diets, but expense of the diet will likely also increase with increasing protein levels.
Additional protein and energy are often required to properly balance diets for growing cattle and lactating beef cows on forage-based diets.
This is especially true when low quality stored forages are the majority of the diet, as is often the case during the winter feeding period after a poor season of fodder production or as a result of low levels of management. 
Limiting dry matter intake on poor quality forages is another concern with regard to the crude protein content of the diet. If a minimum of eight percent crude protein is not maintained in forage crops, cattle will decrease consumption of these poor quality forages.
Generally, forage dry matter intake as a percent of body weight increases until forage crude protein content as a percentage of dry matter decreases below a threshold of about eight percent.
When crude protein is below eight percent, rumen bacteria responsible for digesting forage cannot maintain adequate growth rates.
Forage intake and digestibility will then decrease. Crude protein supplements are appropriate under these conditions to stimulate forage intake.
Forages with adequate levels of crude protein will not require protein supplements to improve intake but may need crude protein supplements if cattle nutrient requirements for crude protein are not being met by the forage alone.
If the forage supplies a minimum of eight percent crude protein, then forage intake will likely decrease with the addition of protein supplements fed at a rate of 0,3 percent of body weight or more as a substitution effect takes place.
Therefore, testing of forage quality is an invaluable tool for determining stored forage crude protein concentrations in advance of feeding.
Protein supplements are available in many forms. High-quality forages, commodity co-product feedstuffs, range cubes, protein blocks and liquid supplements are some examples of protein supplements.
The use of high quality forages such as vegetative legumes and cool-season forages to supply protein in cattle diets when possible should be considered.
Use of commodity-based co-product feedstuffs to supplement forage-based diets for stocker calves and lactating cows for the best supplement values if your operation is set up to store and handle these feeds.
Never feed raw whole soybeans and urea together. Soybeans contain an enzyme called urease that breaks down urea into ammonia.
This combination can be deadly, so avoid feeding NPN sources and soybeans together. This includes soybean stubble and NPN sources offered or fed jointly. 
Signs of toxicity include excessive salivation, rapid breathing, tremors, tetany, and eventually death. Drenching with a gallon of vinegar may be useful if signs are detected early to neutralise the ammonia and prevent more from absorbing into the bloodstream.
Consult with a veterinarian on the best course of action for treating affected cattle. 
When using poor quality forages, cattle performance can be reduced if urea is supplemented in place of a higher quality protein supplement such as soybean meal or cottonseed meal. This includes forage and grain combination diets commonly used as ‘step-up’ rations during the introductory stages of cattle finishing.
Rumen bacteria must have sufficient carbohydrate levels (energy sources) available to them if the nitrogen in urea is to be used effectively. Urea generally works best with high grain diets that are rapidly fermented in the rumen.
The best option usually is to purchase a urea-containing supplement from a reputable feed supplier. Never top-dress urea over feed offered to cattle. 
Providing adequate protein in cattle diets is important for animal health and productivity as well as for cattle farmers’ profitability in Zimbabwe, especially for the important and vital current Command Livestock Programme under way.
Dr Tony Monda holds a PhD in Art Theory and Philosophy and a DBA (Doctorate in Business Administration) and Post-Colonial Heritage Studies. He is a writer, lecturer, musician, art critic, practicing artist and corporate image consultant. He is also a specialist art consultant, post-colonial scholar, Zimbabwean socio-economic analyst and researcher. E-mail:


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