The rumen’s busy bugs

By Dr. Mat Faulkner
One of the amazing things about ruminant animals is their ability to turn feedstuffs with little or no nutritional value into nutritional products.  Ruminants accomplish this through a mixture of rumen microorganisms that convert feedstuffs into energy and protein sources to be used by the host animal.

Essentially, when you feed the cow, you are really feeding the rumen microorganisms.  What you feed them will affect the balance of these organisms and, subsequently, the function of the rumen.

What are they doing?
During fermentation, rumen bacteria break down carbohydrates into volatile fatty acids (VFAs).  These VFAs are the primary energy source for cattle and promote the production of milk and milkfat and weight gain, depending on which VFA is produced.

Additionally, rumen digestible protein is broken down into peptides, ammonia, and amino acids, which are used by the microbes for growth and replication.  If the amount of carbohydrate (energy) is limited or excessive, microbes use the ammonia less efficiently.

When rumen bacteria cannot convert ammonia into microbial protein, it’s converted to blood urea nitrogen and either excreted in urine and milk or recirculated.  Milk urea nitrogen (MUN) is a valuable tool for troubleshooting microbial protein efficiency.

Ideal MUN concentrations will vary from farm to farm, but values below 6 to 8 mg/dl or above 12 mg/dl could indicate a rumen protein inefficiency.  MUN concentrations can also be affected by the degree of corn kernel processing, the time the sample was taken, the number of times the cows are milked, and the milking time relative to feeding.

Feeding the bugs
What you feed the animals changes the types and amounts of bacteria present in the rumen.  This can also change the rumen pH.  For example, feeding higher amounts of effective fiber increases the amount of fiber-digesting bacteria. This results in a positive milkfat response and promotes cud chewing and saliva production, which can elevate rumen pH above 6.0.

However, higher effective fiber can negatively impact milk production by limiting dry matter intake.  To counteract this impact, we feed larger amounts of highly digestible non-forage fiber, such as starch.  This increases the amount of starch and sugar digesters and may decrease the rumen pH below 6.0.

This, in turn, can have its own effects because long-term bouts of low rumen pH from high-starch diets can inhibit fiber fermentation and milkfat production.  For these reasons, whenever you increase non-forage fiber sources, you need to feed an adequate balance of effective fiber to maintain the rumen mat and limit passage rate from the rumen.

Trace minerals matter
Until recently, most rumen fermentation research has focused on macronutrients.  Research teams at Penn State University and The Ohio State University have now detailed the effects of trace minerals on microbial fermentation.  When fed an organic trace mineral supplement, Penn State researchers observed elevated VFA production, while researchers at The Ohio State University observed higher neutral detergent fiber (NDF) digestion in lactating cows.

Although the exact mechanism behind these effects is unknown, we now know rumen microorganisms have a requirement for trace minerals.  However, in vitro research has shown excessive trace mineral supplementation from sulfate sources can be toxic to certain microbial populations.

Other non-nutrient related factors that can affect microbial fermentation are particle size, sorting and slug feeding, all of which can affect nutrient retention and pH levels.

When it comes to achieving optimal microbial fermentation and animal performance, it is essential to maintain this delicate balance of fiber and carbohydrates.

This article was originally written for the March 10, 2017 issue of Hoard’s Dairyman.

About the author: Dr. Mat Faulkner joined the Vita Plus team in 2016 as a dairy specialist in southwest Wisconsin, eastern Iowa and northern Illinois.  He started his agricultural career working on his family farm before enlisting in the U.S. Army in 2006, where he served as sniper team leader for the Reconnaissance Platoon and received high marks upon discharge in 2009.  He then attended Illinois State University to earn his bachelor’s degrees in animal science and agriculture business management in 2011 and a master’s in agriculture science in 2013.  From there, he received his doctorate in animal science from The Ohio State University in 2016.