Maximizing Rumen Bacterial Growth and Forage Digestion
Several recent Block Blogs have discussed various aspect of feeding cattle to get the most out of the available forage. Mark Robbins discussed the use of Non-Protein Nitrogen and Dan Dhuyvetter reviewed how a natural brown seaweed meal called Tasco® and how they impact forage digestibility through improved rumen function. If we examine rumen function at the microbial level we get a better understanding of how nutrient and additive delivery through a low moisture block (LMB) self-fed supplement like CRYSTALYX® can dramatically improve fiber digestibility.
Rumen Microbial Populations and Rumen pH
The rumen is a large fermentation vat, with a total volume of 40-50 gallons for a 1500 pound beef cow. The rumen provides a site where billions of rumen microorganisms can digest carbohydrate, proteins and fiber. These microbes convert feedstuffs into energy in for the form of volatile fatty acids (VFA) and microbial protein that can be utilized by the animal. Rumen bacteria can be grouped into different categories depending on the material they digest. It is estimated, there are over 100 billion bacteria in the rumen. Protozoa and rumen fungi (yeast) make up the remaining microbial population.
The microbes are very sensitive to rumen pH and nutrient supply. At pH between 6 and 7 the VFAs produced are acetate (50-65%), propionate (18-20%) and a small amount of butyric acid (10-18%). Acetate and butyric acid is utilized for body fat and milk fat synthesis. Propionate is utilized to maintain blood glucose levels. A small amount of butyric acid is used as an energy source for the cells lining the rumen wall. At pH 6 to 7 and the resulting VFAs provides an optimal amount of energy and microbial protein to the cow. The predominate bacteria are the fiber digesters. Rumen pH below 5.8 will shift the microbial population from primary fiber digesters to starch digesters. These microbes will produce lactic acid. The amount of feed and how quickly it is consumed will impact rumen pH. Feeds high in starch will result in rapid fermentation and a subsequent drop in pH. In general, as the forage to concentrate ratio decreases, the acetate to propionate ratio drops. If pH drops below 5.5 there is a risk of acidosis due to the accumulation of lactic acid. The bacteria that digest fiber die and it can be several days before their numbers return to normal levels. The rumen is in a constant flux and maintaining a balance of the microbial population is critical to maximizing forage digestion.
Rumination and the Benefit of Saliva
Cows that are chewing their “cud” for 8-10 hours per day will recirculate about 45 gallons of saliva. Cattle are great at recycling. The saliva is composed on sodium, potassium, chloride and bicarbonate ions. These minerals are recycled back to the rumen and act as a powerful natural buffer helping maintain a consistent rumen pH. Saliva also helps make the cow more efficient in nitrogen metabolism. As proteins are broken down in the rumen ammonia is produced. Fiber digesting bacteria require a certain level of nitrogen available in the rumen as ammonia. When there is excess nitrogen in the rumen it is absorbed and recalculated through the saliva. In general, as the level of grain in the diet is increased, the amount of rumination and saliva produced is decreased which can result in the rumen function being less efficient due to the loss the natural recycling of buffer and ammonia. LMB supplements will stimulate saliva production due to the licking action need to consume them. There is an enhancement in rumen function beyond just the nutrients that the LMB supplies.
Nutrient Deliver Impact on Net Nutrient Availability
Feedstuffs are analyzed for energy and crude protein content. These are lab methods that estimate nutrient content based on chemical analysis. However, the true nutrient value is what the cow is able to digest. We often think of corn as an energy source, but research has shown that 3 pounds of corn fed in a diet of low quality forage resulted in reduced fiber digestion compared to 1 pound of LMB. The sugars in the LMB do not lower pH like the starch in corn and are consumed over a longer time frame. The net result of corn diet was less energy being made available to the animal due to lower forage digestion. On paper, the nutrient analysis of the hay in the diet was the same for the corn and LMB treatment. However, the amount of nutrients metabolized from the forage was much higher for the LMB treatment.
In practical terms, the energy content of forage is more dependent on how it is fed and the other ingredients in the diet than what the lab reported energy content. We have seen instances where one farm will have exceptional animal performance and another farm with very similar forage will have poor animal performance. If we look at digestion at the microbial level we are able to explain some of these differences. Were there different methods of feeding and what were the other ingredients in the diet? Often a nutritionist or cattle producer will doubt the benefit of delivering 0.5 to 1.0 pound of a LMB supplement. CRYSTALYX® offers a wide variety of self-fed supplements for a variety of forage quality and feeding situations. At the rumen microbial level, a consistent supply of rumen friendly carbohydrate and protein and a stable rumen pH can result in optimal performance and maximizing your forage.
