You buy a high-protein feed, follow the feeding instructions and expect better results. Yet your animals may still gain weight slowly, lose condition or produce less milk than expected.

What could be missing?

The protein percentage on the bag tells only part of the story. For cattle, sheep and goats, where protein is used during digestion matters too. Understanding this can help farmers choose supplements that suit their grazing, animals and production goals.

Two terms explain much of this: rumen-degradable protein (RDP) and rumen-undegradable protein (RUP), commonly called bypass protein.

Your animal feeds a workforce inside its stomach

Cattle, sheep and goats have a rumen: a large digestive compartment containing billions of microorganisms, often called rumen microbes.

Think of these microbes as a workforce that helps process grass, hay and other feeds. They need nutrients and energy to grow and do their work. Later, many of the microbes pass further along the digestive system and are digested themselves, providing valuable protein to the animal.

This means a ruminant gets usable protein from two important sources: the microbes it produces and feed protein that escapes breakdown in the rumen.

A good feeding program supports both sources.

RDP: protein that feeds the rumen workforce

RDP is the part of feed protein that microbes break down in the rumen. They use the resulting materials, together with energy from feed, to build microbial protein.

RDP is therefore useful protein. Although microbes use it first, the animal benefits from their activity and from digesting them later.

This is particularly relevant when animals graze mature, dry veld.

When forage is short of protein, microbial activity can be restricted. Appropriate protein supplementation can improve forage intake and digestion, helping animals obtain more nutrients from the roughage available.

Practical example: A farmer has mature beef cows on plentiful but poor-quality winter grass. A suitable protein lick may help them use that grass more effectively.

However, a lick cannot replace missing grazing. If there is too little roughage, or the animals still cannot obtain enough energy, additional feed is needed.

RUP: protein that takes a different route

RUP escapes breakdown in the rumen and travels further through the digestive system. The digestible portion can then supply amino acids the building materials animals use for muscle, milk and other body functions.

This is why it is called bypass protein: it bypasses rumen breakdown, not the whole digestive system.

Bypass protein can help when microbial protein alone does not meet the animal’s needs. Growing animals are one example. But more bypass protein does not automatically mean better performance; the rest of the diet still needs to support the rumen.

Its quality also matters. Protein that escapes the rumen but is poorly digested afterwards offers limited benefit.

RDP and RUP work together

Most natural protein feeds supply a mixture of RDP and RUP. The proportions vary with the ingredient and how it has been processed.

For example, soybean meal provides both fractions, while appropriate heat treatment can increase the proportion that escapes rumen breakdown. Excessive heating, however, can damage protein and reduce its usefulness.

The feeding decision is therefore about balance:

• Enough RDP to support the microbes.
• Enough digestible bypass protein where the animal needs it.
• Enough energy for both microbial activity and production.

Buying a bypass supplement while leaving the rumen short of nutrients can limit the return on that purchase.

Where does urea fit in?

Some protein licks and concentrates contain non-protein nitrogen (NPN), commonly supplied through feed-grade urea.

Urea is not true protein and does not supply amino acids directly. Rumen microbes can use its nitrogen to manufacture protein when suitable energy is available.

It can be a useful, economical ingredient in properly formulated ruminant feeds. South African research with cows on winter grass veld has demonstrated its value as a source of supplemental rumen-degradable nitrogen under controlled feeding conditions.

However, urea does not provide bypass protein, and it is not a direct substitute for every natural protein source.

Incorrect mixing or excessive intake can cause rapidly developing, potentially fatal poisoning. Follow the product’s instructions, including adaptation and intake limits. Do not add extra urea to an existing lick or feed without a qualified formulation, and do not use urea-containing adult feeds for young animals whose rumens are not yet functioning adequately.

Do fattening animals need more protein than cows approaching calving?

Sometimes, but the comparison needs care.

Young animals growing rapidly often need a higher protein concentration because they are building substantial muscle. As finishing animals mature, their protein concentration requirement may decrease while energy remains important for further weight gain.

A mature pregnant cow has different demands. Her requirements increase during late pregnancy, and milk production raises them further after calving. A pregnant heifer also needs nutrients for her own growth.

A higher percentage in the diet also does not necessarily mean more protein consumed each day. A large cow can eat more feed than a smaller growing animal.

The useful question is: What does this group need, and what is its current diet already supplying?

Match protein choices to the production system

Animals practical feeding priority

Mature animals on protein-deficient dry veld

Support rumen activity with suitable degradable protein or nitrogen; check that enough roughage and energy are available.

Young growing cattle, lambs or kids

Supply sufficient usable protein for growth while supporting the rumen; additional bypass protein may be useful.

Finishing animals

Balance protein with energy, effective fiber and the intended growth rate. A higher protein percentage alone does not guarantee faster gains.

Cows approaching calving

Meet rising pregnancy requirements and protect body condition; assess the whole diet before choosing a supplement.

Lactating animals

Match protein and energy to milk production; high-producing animals may benefit from additional digestible bypass protein.

These are priorities rather than fixed recipes. The same supplement will not suit every farm or every group.

Read beyond “crude protein” on the label

Crude protein (CP) is an estimate based on the nitrogen in a feed. It can include nitrogen from both natural protein and NPN sources such as urea. Consequently, two products with the same crude protein figure may supply protein differently.

Also check the units:

150 g/kg crude protein means 15% crude protein.

Then establish whether the product is a complete feed, a supplement or a concentrate requiring mixing. A high-protein lick fed in small amounts cannot be compared directly with a complete ration fed in kilograms.

A simple hypothetical example illustrates this:

• A 40% CP supplement fed at 250 g supplies 100 g of crude protein.
• A 16% CP feed fed at 1 kg supplies 160 g of crude protein.

These are arithmetic examples, not feeding recommendations. They show why percentage and daily intake must be considered together. They still do not tell you how much usable protein ultimately reaches the animal.

If RDP and RUP are not shown on the bag, ask the supplier for technical information.

Five questions to ask before buying feed

1. Which animals and production stage is this product designed for?
2. What does it add to my existing grazing or roughage?
3. How much crude protein comes from NPN, and what natural protein sources are included?
4. Does it supply bypass protein, and is that useful for this group?
5. What daily intake, mixing and adaptation instructions must I follow?

Where possible, test your hay or other major feed ingredients. This helps identify what is missing before you spend money on supplements.

Monitor results through body condition, growth, milk production and actual feed intake. If performance remains poor, investigate the whole feeding program and animal health rather than automatically buying a higher-protein product.

Choose protein for the job it must do. Feed the rumen properly, meet the animal’s production needs and judge a product by its contribution to the complete diet not simply the biggest number on the bag.