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Feeding the cow feeds the bugs

Bill Seglar Published on 09 August 2013

Dairy feeding programs have become so sophisticated that sometimes the basic goals of feeding ruminants are forgotten. Many feeding issues can be resolved by tending to the basics of rumen physiology.

In short, the ration formulation and delivery process involves feeding a fermentation vat full of microbes. These microbes are primarily responsible for generating fermented, nutrient-rich end products which meet the vast majority of a cow’s diet requirements.



Microbial basics

Two parts of the ruminant’s four-compartment stomach serve as this fermentation vat. They include the rumen and reticulum – referred to as the reticulorumen.

Within each drop of fluid in this vat reside one to two billion bacteria and 50,000 protozoa, along with beneficial fungi. The ultimate goal of this multitudinous microbial population is to work in synergy via enzyme production.

In brief, enzyme production degrades complex nutrients such as carbohydrates, where starch and fiber are degraded into glucose – the basic energy unit on which all life depends.

This same enzymatic degradation process works on the protein side until nitrogen, in its free form, is available for microbial use – nutritionists refer to this as soluble protein.

The primary functions of microbes during their life cycle is maintenance, growth and reproduction. Therefore, microbial biomass production becomes crucial, and microbial protein serves as the greatest amino acid-balanced protein source for the cow.


The more efficient the rumen microbes are at producing high levels of microbial protein, the less supplemental bypass protein is required in the ration.

A happy synergy between the rumen microbes and the cow must exist to produce two classes of microbial end products: acids – both volatile fatty acids (acetate, butyrate and propionate) and lactic acid – which supply 50 to 70 percent of the cow’s energy needs, and microbial protein, which supplies 50 to 60 percent of the cow’s protein needs.

Ruminal goals for microbes

The balance of nutrients fed to the cow achieves three ruminal microbe goals: The first is a proper ratio of carbohydrates.

Carbohydrates are made up of several components: starches, sugars and pectins, which are rapidly fermented, and fiber – measured as ADF and NDF in laboratory reports – which is slowly fermented by rumen microbes.

The second goal is a proper ratio of both rapidly and slowly degradable rumen protein sources. Nonprotein nitrogen, such as urea and other short-chained amino acids and peptides (soluble protein), are rapidly available to microbes.

The more complex and longer-chained amino acid proteins are released more slowly for microbial utilization. The carbohydrates or proteins not fermented by the rumen microbes enter into the small intestine for enzymatic digestion processes; this is called monogastric digestion.


The third ruminal microbe goal is to provide sufficient particle fiber length in the ration to meet reticulorumen scratch factor needs to maintain a functional and healthy fermentation vat.

Data and analysis

These rumen physiology events, called rumen kinetics, are not static but occur continuously. This is why more advanced methods of studying digestion use gas-production systems that record thousands of data points of total gas production over a 48-hour time period.

Most of the gases produced by microbes during the fermentation process are a combination of carbon dioxide and methane.

This is accomplished by placing a dried 6-mm ground forage sample, with buffered rumen fluid, into a closed test vial fitted with a pressure transducer.

The gas pressure in the headspace is measured as an electronic reading; this measurement is then transferred into a computer application, which graphs the amount of gas produced during the 48 hours.

“Curve peeling” software then calculates two gas-production curves, representing rate of digestion and mL of gas produced from fermented carbohydrates (which is both rapidly and slowly available to rumen microbes).

The “fast-energy pool” includes primarily starch, sugar and pectin. The “slow-energy pool” includes primarily NDF, which is basically the cell wall fiber complex.

These energy pools are not homogeneous, meaning that some starch, sugar and pectin respond like slow-pool energy (because they are locked up in the cell wall complex), and some fiber material acts like fast-energy.

Gas-digestion kinetics analyses provide great value to dairy nutritionists. This is because high-milk-producing dairy cattle have fast rumen passage rates. Therefore fermentable carbohydrates need to ferment as fast as possible, prior to escaping the rumen.

The fiber that escapes rumen fermentation may be further fermented in the large intestine; however, much of the microbial protein and volatile fatty acids are lost in manure.

The greatest finding of a gas-digestion test is its quantification of the carbohydrate digestibilities of forages during a 15-hour to 18-hour rumen residence, compared to present-day fiber digestion commercial-test offerings, which are static measurements at 24-hour, 30-hour or 48-hour time periods.

A commercial gas digestion test is available through Dairyland Laboratories.

In the end

The fate of microbial fermentation end products determine the productivity of dairy cattle – specifically, milk production and the milkfat and protein components.

The acetic and butyric fatty acids are primarily responsible for milkfat synthesis in the mammary system, while propionic and lactic fatty acids undergo biochemical conversions in the liver to produce glucose.

The glucose is then used by the cow for body functions, which include maintenance, growth, reproduction and milk production. The microbial protein is responsible for milk-protein synthesis, along with all the other body functions of the ruminant.

Ruminants have to be fed and managed properly so that ideal rumen health exists; this is critical for maintaining this robust mix of rumen microbes.

The healthy rumen environment requires consistent pH in the 5.3 to 5.8 range, and the rumen needs to be moving, or ruminating, constantly.

The goal of dairy feeding is to stabilize rumen fermentation by maintaining feed consistency and scratch factor for reticulorumen stimulation. This results in desired rumination, regurgitation and cud chewing by the cow.

Rumen fermentation production of acids forces pH downward and produces an environment unsuitable for healthy microbial activities. The regurgitation and cud-chewing response of the cow produce massive amounts of sodium bicarbonate from saliva.

So when the cud is re-swallowed, the buffering effect of the bicarbonate neutralizes the acidic rumen environment and brings pH back up into the 5.8 to 6.5 pH range.

Less-than-ideal rumination results in an array of digestive upsets: from cows reducing their feed intakes to acidosis disease events, and under more severe situations, lameness due to laminitis in the feet.

Thus, feeding ruminants requires high-quality, palatable and consistent forages. Factors that help meet forage quality goals include:

  1. Forages that originate from hybrids and varieties with the same nutrient profiles
  2. Consistent forage chop lengths
  3. Forages ensiled or baled using practices that maximize forage consistency and palatability
  4. Fresh, never spoiled, feedstuffs
  5. Constantly monitor for feed composition changes, especially with ensiled wet forages
  6. Frequent feedings

Maximizing production efficiency helps ensure the ultimate goal: feeding high-quality forages to dairy cattle.

Achieving efficient carbohydrate utilization and ensuring proper soluble protein sources mean more efficient rumen microbial activities. That translates into higher feed efficiencies, weight gains, milk production and healthier livestock. PD

Bill Seglar
  • Bill Seglar

  • Senior Nutritionist Veterinarian
  • DuPont Pioneer - Global Forages
  • Email Bill Seglar