All you need to know about bypass protein

Plant-based protein is an important source of amino acids for the dairy cow. During digestion, however, the majority of this valuable protein is broken down in the rumen of the cow, far too early in the digestive system for it to be fully utilised.

Bypass protein products overcome this problem by protecting the protein while in the rumen, but allowing it to be fully digested within the small intestine. Consequently, better utilisation of the essential amino acids occurs, resulting in improved milk production.

Table of contents

      1. The ruminant digestive system

      Cows are amazing!  They eat grass and make milk.  They convert something that is indigestible into yoghurt, cheese, and ice cream!  But cows do not actually digest the grass; bacteria do that in the cow’s rumen. 

      The rumen is the cow’s first stomach chamber. It resembles a very large wineskin.  It is warm and full of liquid, the perfect environment for bacteria.  Every so often the cow will add some fuel – grass. 

      Did you know that cows do not have front teeth in their upper jaw?  When they graze, they rip grass up with their lips and tongue. The unchewed mass goes into the rumen and makes a floating mat on the surface. 

      Sometime later the cow will relax in the sun, regurgitate some of this material, and leisurely chew on it.  When the cow chews its cud, it uses its molars to grind the fibre, making it smaller and easier for the bacteria to digest.

      ‘Cows’ are specifically female bovines that have produced a calf.  Before calving, they are heifers.  Male bovines are bulls, or steers if they have been castrated.  When you see a herd of these large animals, it is appropriate to call them ‘cattle’, not cows.

      2. What is bypass protein?

      ‘Bypass’ or ‘Rumen Escape’ protein is simply a protein that is less likely to be digested by rumen microbes.

      Cows need nutrients to produce milk. The bacteria in the rumen provide them with both energy and protein as they digest grass. If cows are to produce more milk, they need nutrients beyond what the bacteria can supply.

      Typical dietary supplements are corn for energy and soybean meal for protein. The cow can digest these feedstuffs, but so can the bacteria. Bacteria will digest 60% of the protein in soybean meal, breaking it down to ammonia, and then using that to synthesise their own microbial protein. 

      As the level of supplemental soybean meal increases, the bacteria continue to digest it, but are unable to keep up with re-synthesising the protein. Ammonia builds up in the rumen and moves into the bloodstream, increasing the levels also in the urine and milk, which indicates a waste of protein.

      ‘Bypass’ or ‘Rumen Escape’ protein is simply a protein that is less likely to be digested by rumen microbes.

      3. Are bypass proteins natural and safe?

      Some examples of ingredients that naturally escape digestion by rumen microbes include fish meal, blood meal, and feather meal. A more popular option is ‘protein modified’ soybean meal, which is still a natural and safe feed ingredient. But it has been modified to make it less soluble and resistant to digestion by rumen microbes, yet remaining digestible to the cow itself.  Typically, this protein modification will allow 40 – 85% of the protein to pass through the rumen undigested – ‘bypassing’ the rumen microbes.

      4. How are different types of bypass protein made?

      The most common way to modify soybean protein is to heat it until it begins to brown.  This is caused by the Maillard reaction, which is also responsible for the browning of toast. Heated carbohydrates react with lysine to form melanoid polymers. This reduces the solubility of the protein but also causes some loss of lysine. Adding carbohydrates such as sugars can facilitate the browning reaction and reduce the amount of heat required. 

      There are two basic types of bypass soybean meal produced by heat treatment: expeller modified and protein modified.  When beans are processed through an expeller to extract oil, the expeller creates a lot of frictional heat.  That heat may improve the bypass protein level to 40 - 60%. 

      Most soybeans are crushed and the oil extracted with hexane.  Heat is used to remove and recover the hexane.  Additional heat is applied to denature a protein called trypsin inhibitor.  The resulting meal has a Rumen Undegradable Protein (RUP) level of 30%.  

      5. How is bypass/ Ruminal Undegradable Protein (RUP) measured? 

      A small sample of the protein is sealed in a Dacron bag and suspended in a cow’s rumen.  After 12 – 16 hours, the bag is removed to determine the amount of protein that remains undigested. Alternatively, the bag might be incubated in a beaker with artificial saliva and fresh rumen fluid containing microbes.  The percentage of protein that remains in the bag is reported as RUP.

      RUP = Rumen Undegradable Protein

      6. Are bypass proteins expensive?

      The extra processing required to produce bypass protein adds cost to the ingredient, usually 10 – 20% above the price of an untreated one. The payback comes when the extra milk is sold. Typically, cows consume 1 – 2 kg of bypass protein a day, which is less than 5% of their total intake.  From that additional protein, you should expect an extra kilogram of milk production.

      7. Can ingredients other than soybean meal be processed for bypass protein?

      Yes, canola/rapeseed and any other plant-based protein meals can be successfully treated.

        

      8. Is bypass protein fed to any other animals besides dairy cows?

      Bypass protein can also be fed to dairy goats, sheep and other ruminants. Young, rapidly growing beef cattle can also benefit. However, bypass protein adds to the feed cost, and beef cattle need to be fed for several months before being sold. Pigs and chickens can eat Bypass protein too, but it would not provide any advantage and only add to the feed cost.

      Bypass protein is fed to deer during peak antler growing season to help produce trophy racks.  It is also used in mushroom production because it is a protein source that resists bacterial growth.

      9. Can cows get too much bypass protein? 

      Yes, but without harming the cows. Extra protein will not be beneficial if it exceeds the level of energy available to produce milk. Then, it is just wasted resources. It is also critical to make sure that the microbes have enough protein that they can digest in order to thrive. The microbes digest the fibre, build microbial protein and produce the energy which is deposited in the milk fat. Eventually, these microbes move with the digesta into the post-rumen stomach chambers where they are digested and used to make milk proteins.

      10. Is bypass protein digestible? 

      Soybean meal has about 8% protein that is fully indigestible. It may increase to 10% when processed to make the protein bypass. Improperly processed blood meal and feather meal may have good bypass, but also be highly indigestible.

      11. How are bypass proteins different from bypass amino acids? 

      Amino acids are protected by coating a specific amino acid with material that will not dissolve in the rumen.  This coating may account for 50% of the mass.

      Bypass proteins are a collection of various amino acids that have little or no diluting material. In the case of bypass soybean meal, the amino acid content is about 50% of the dry matter. The remaining 50% is primarily carbohydrate that is available as an energy source.

      12. Conclusion

      The rumen gives the cow a unique ability to convert grass into milk.  This requires the action of bacteria in the rumen to break down forage proteins and resynthesise them into highly nutritious microbial protein.  Rumen bypass protein avoids microbial digestion and adds to the total amount of metabolisable protein available for milk production.