Microbial Protein Production and Ration Digestibility Variation?

Rick Grant
William H. Miner Agricultural Research Institute

Increasingly, the focus in ration formulation is on metabolizable protein (MP) and individual amino acids. This move from crude protein to MP and now to amino acids means that we can feed dairy cows more precisely and enhance the efficiency of nitrogen use for milk protein production. However, we need to remember that the focus must still remain squarely on the rumen fermentation which supplies 50-70% of the cow’s protein needs. The amino acid composition of rumen bacteria matches the amino acid profile of milk protein more closely than other feed ingredients making microbial protein the ideal fit when attempting to meet the cow’s amino acid requirements. In particular, the amino acid composition of microbial protein contains more methionine and lysine than common oilseed meals and legume grains.

Supply Individual Amino Acids

With the advent of rumen-protected amino acid products for lysine and methionine, we now routinely focus on balancing rations for these amino acids. There is always the risk that we formulate rations using nutrition models without understanding the inherent variability in microbial protein supply and the fact that models do have errors associated with them. In other words, how well do our current models predict microbial protein and amino acid flow to the small intestine? Also, how variable is the supply of amino acids provided to the cow?

Nutrition models are static and so provide only a snap-shot in time of what is actually occurring dynamically within the cow from meal to meal, throughout the day and over several days. Still, published research summaries indicate that the correlation between observed and predicted duodenal flow of methionine is about 0.85. You might predict that this relationship would be even tighter when focused on one herd or one pen within a herd.

Why the Variability in Response to Amino Acid Balancing?

There are many reasons why nutrition models don’t always accurately predict cow responses to amino acid balancing including:

  • Amino acids other than the ones we are focused on are truly limiting
  • Inaccurate model predictions of both metabolizable protein supply and individual amino acids
  • Management factors that cause variation in cow feeding behavior that influences rumen fermentation of rations
  • Variation in optimal rations at different stages of lactation
  • Digestibility or availability of various protein and amino acid sources (blood meal is a good illustration of this variability)
  • Digestibility of energy components (starch and forage)

It is likely that amino acid supply does not entirely explain milk protein responses. Recent research suggests that the efficiency of MP use for milk protein may well decrease as supply of MP increases. Additionally, research from the 1980s found much stronger relationships between milk protein and dietary energy intake versus dietary protein consumption. This relationship between energy and microbial protein, at least in part, reflects the tremendous importance of ruminal fermentation to microbial protein production and MP supply. Consequently, variations in fermentation level and efficiency translate into variable amino acid delivery to the cow.

What Do We Think We Know About Amino Acid Variability?

Let’s focus on methionine. For high producing cows the methionine supply is considered sufficient at 2.2% of MP (or about 60 g/day of methionine). But, we generally provide more than 2.2% of MP just to ensure that it is not limiting if variations in other nutrient supply occur, or if variable rumen conditions limit microbial protein production. In preparing this article, I asked Dr. Heather Tucker a post-doc here at Miner Institute (now working for Novus) and a budding amino acid expert about her thoughts on actual variability in methionine supply. Much of this section reflects our combined thoughts. We concluded that, if the cow is being managed properly for good cow and ruminal health, then methionine supply from the rumen microbes may not vary tremendously.

Of course, assuming consistent rumen fermentation depends on the ration, forage quality and consistency, and the feeding environment. Importantly, variability in forage NDF content and digestibility, starch content and digestibility, and protein fractions may well result in anything but a consistent supply of amino acids. If cows are experiencing substantial variability in rumen conditions, then cows will be moving from a negative methionine balance to a positive balance on a weekly or even daily basis. Under these conditions, it is easy to infer that milk protein production (to say nothing of her overall well-being) would be compromised.

For cows producing 100 lb/d or more of milk, if microbial protein were to vary by 50 to 100 grams, that would not be a large amount for methionine assuming about 3800 g/day of MP with 45% of that from microbial production (or about 1710 g/day microbial protein). However, for a more modest level of milk production – for example 85 lb/day – MP will be around 2500 g/day rather than 3800. Therefore, total potential methionine could range between about 70 and 110 g. Daily variations in microbial protein production would be much more important at the lower end of this range. For our Miner Institute herd, we routinely supply about 20 g/day above the 60 g/day requirement for methionine.

If variation in ration quality and(or) feeding management were to result in about 10-15 g/day less methionine supply, could the cow actually detect that deficit and experience a noticeable loss in milk protein? A fluctuation of 10-15 g/day in methionine may well be noticeable if you are supplementing 12 grams of protected methionine.

How Do You Promote Rumen Microbial Protein Synthesis?

Even though good dietary and feeding management minimizes the variability in microbial protein synthesis, microbial protein synthesis may vary substantially among cows fed different diets or even among cows fed the same diet but experiencing different management environments. Research indicates that diets containing a blend of high-quality forages and concentrates increase the efficiency of microbial protein synthesis because of an improved rumen environment for the growth of more diverse bacteria species.

Greater and more consistent microbial protein production is most highly related to 1) higher and consistent dry matter intake, 2) amount and type of protein, 3) supply of fermentable energy, mainly from carbohydrates, 4) rumen environment, especially pH, and 5) passage rate. Fermentability of fiber and other carbohydrates drives microbial protein synthesis. Consequently, factors that increase rumen fiber digestibility can have a large impact on microbial protein production. For example, on average legumes have 20% greater rate of NDF digestion than grasses and immature forages may have 50-60% greater rate of NDF digestion than mature forages. Any treatment of forage fiber or feed additive that improves fiber digestion similarly can boost microbial protein production by up to 20 to 25%. Generally, anything that maintains a consistently higher rate of rumen fiber digestion will ensure a higher and more consistent flow of microbial protein to the small intestine.

Research reported at this October’s Cornell Nutrition Conference by Dr. Dave Barbano (professor of Food Science at Cornell University) proposed another important reason to maintain optimal rumen conditions conducive to fiber fermentation. In a large data set comprised of farms in Vermont and Northern New York, he found that the proportion of de novo synthesized fatty acids in milk fat was highly correlated with greater milk fat and milk protein percentage. High de novo synthesis of milk fatty acids should reflect optimal rumen conditions for fiber digestion and consequently greater milk components.

The Bottom Line

Variability in amino acid flow is real, but if the cows are well managed and microbial protein production is high, then the effect of variation is mitigated. Accurate inputs for nutrition models are critical and providing a realistic “formulation cushion” for MP and amino acids such as methionine ensure that unavoidable variations in microbial protein production do not push the cow into insufficiency, but only brings them a little closer to the actual requirement. Focusing on basics of forage quality, feeding management that ensures adequate feed availability 24/7, and cow comfort will optimize rumen fermentation and cow performance – focus your efforts on forages, rumen efficiency, and microbial protein supply, and then there will be less need to worry about ordinary variations in amino acid supply.

Amaferm Application

The most challenging job of the nutritionist is to economically formulate for optimal production. Focusing on balancing amino acid levels and reducing crude protein has been one of the strategies in recent years to assist in that challenge. Why keep Amaferm in mind when balancing amino acids and lowering protein cost to optimize performance?  Energy.

One of the main factors involved in the variation of microbial growth and subsequent microbial flow is energy from fermentation. As shown in the below graph (Patterson et al. 2006) there is a direct correlation between more digestible energy and microbial protein production. So the real focus to increase microbial protein and reduce the variation in MP flows lies in increasing digestible energy (ruminal).

Patterson Graph

Amaferm is one of the most researched rumen modifiers on the market when it comes to forage fiber digestion. On average, Amaferm increases NDFD by 17% minimizing the negative variability of forage. In addition, Amaferm has in vitro and in vivo studies showing an increase in microbial protein production of an extra 100-450 grams of microbial yield. More digestibility and more microbial protein delivers more energy to the animal so the producer gets more performance.


Click here to help us connect you to the easiest way to add Amaferm to your rations.

Leave a Reply