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"Our biggest source of livestock feed is grass! Humans can't get nourishment from it, but huge tracts of the earth's land are too dry,
too steep or too rocky for grain. We let cows and calves harvest sparse crops of grass from massive tracts of the American Great Plains,
Canadian Prairie Provinces, the Australian Outback, New Zealand, the sandy steppes of Hungary and huge tracts of Khazakstan —
to name but a few grasslands."
— Dennis Avery, The Hudson Institute, speaking at the 2011 TSCRA Convention Weekend opening general session

 

How Does the Cow's Digestive System Work?

By Robert Fears

If we are to properly feed cattle for optimum production, we need to understand their digestive system.

Cows are ruminants like goats, sheep, and deer. Their digestive systems vary greatly from those of monogastric animals such as man, dogs, poultry and swine. Ruminants have a 4-compartment stomach. Monogastric animals have a 1-compartment stomach. Unless you are an animal nutritionist, this is where your understanding of the cow's digestive system may end.

About 2 years ago, I had the opportunity to watch Dr. Joe Paschal of Texas A&M AgriLife Extension pull a cow's digestive tract from a big plastic bag in front of an audience at the Texas and Southwestern Cattle Raisers Association (TSCRA) School for Successful Ranching. Paschal laid the organs on a table in an orderly fashion and began explaining how a cow digests her food, starting with the esophagus. Here's a recap of Paschal's presentation.

Food digestion

In 2011, Dr. Joe Paschal of Texas A&M AgriLife Extension pulled a cow's digestive tract from a big plastic bag in front of an audience at the Texas and Southwestern Cattle Raisers Association (TSCRA) School for Successful Ranching. He laid the organs on a table in an orderly fashion and began explaining how a cow digests her food starting, with the esophagus.

In a separate class, the lecturer discussed how wildlife species, such as deer, digest food. The 2013 School for Successful Ranching will offer more education on topics of interest to cattle raisers March 21 to 23 in Fort Worth.

It takes 1 to 3 days for food to pass through a cow's digestive tract, depending upon what she eats. A cow briefly chews food as she eats, breaking it into smaller particles. As she chews, digestive enzymes in her saliva are mixed with the food before it passes down the esophagus into the reticulum and rumen.

Since digesta flows freely between the reticulum and rumen, these compartments are collectively referred to as the reticulorumen. The reticulorumen contains more than 50 percent of the total digestive tract capacity.

Most feed is fermented in the reticulorumen, but a small amount may pass unchanged into the omasum and abomasum. Some of the larger food particles are regurgitated, chewed again and re-swallowed. This is "chewing the cud."

Food is fermented and further broken down in the rumen by microbes. The stable environment in the rumen with a pH of 5.5 to 7.0 and a temperature range of 37 to 40 degrees Celsius is conducive to microbial growth.

There are several kinds of rumen bacteria, and each is specific to the type of food they utilize and the end products they produce. Rumen bacteria digest cellulose, hemicellulose, starch, sugar, organic acids, protein or fat. There are bacteria that produce ammonia and methane or synthesize vitamins.

The specificity of rumen bacteria is why livestock specialists and animal nutritionists recommend that changes in feed be transitioned slowly. Populations of bacteria that digest the new feed have to be established or the cow will have adverse reactions to the new diet.

Bacteria and other microorganisms are ingested on feed or obtained from other animals. If the cow eats feed that her rumen bacteria utilize, the population will grow. As the population grows the cow can digest more of the food she eats. If a cow doesn't eat what her rumen bacteria utilize, the microorganisms die. This is why cattle raisers say that they feed rumen "bugs," not the animal.

Protozoa, larger than bacteria, are found in the rumen and are classified according to their cell morphology. Species vary according to the type of diet, time of year and geological location. Both bacteria and protozoa have food value to the cow. Dried microbes contain 40 to 50 percent crude protein and are more than 75 percent digestible.

Digesta flows from reticulorumen into the omasum which contains 6 to 8 percent of the digestive tract capacity. The omasum has many folds of tissue that resemble a partially open book. Water is reabsorbed from digesta and particle size is further reduced in the omasum.

Upon leaving the omasum, digesta passes into the abomasum that is often referred to as the true stomach. The abomasum secretes digestive enzymes that break feed down into protein, vitamins, simple carbohydrates, fats and amino acids for absorption into the small intestine. Undigestible material passes into the large intestines where excess moisture is reabsorbed and fecal material is formed.

The uniqueness of a ruminant
Ruminants have the unique ability to convert roughage into protein and energy through their microbial/enzyme digestive systems. Because of this ability, cattle and other ruminants play an important role in the earth's ecology and in our food chain.

We were fortunate to hear Dennis T. Avery from the Hudson Institute speak at the same TSCRA conference at which Paschal did his demonstration. Avery explains the role of the cow: "Our biggest source of livestock feed is grass! Humans can't get nourishment from it, but huge tracts of the earth's land are too dry, too steep or too rocky for grain. We let cows and calves harvest sparse crops of grass from massive tracts of the American Great Plains, Canadian Prairie Provinces, the Australian Outback, New Zealand, the sandy steppes of Hungary and huge tracts of Khazakstan — to name but a few grasslands."

Avery continued, "Livestock happily and constructively eat lots of other stuff that humans can't or won't consume, including millions of tons of peanut hulls, citrus pulp, molasses, feather meal, wheat bran, meat and bone meal from slaughter plants, corn gluten meal, and on down a long list. Without livestock, you have no more food for humans, and a huge waste disposal problem."

In addition to Avery's long list of cattle feed ingredients, microorganisms in the cow's rumen can manufacture protein from non-protein nitrogen such as urea, biuret and ammonia. Non-protein nitrogen is more economical than plant protein and gives cattlemen and animal nutritionists more options for feed rations. Rumen bacteria convert non-protein nitrogen into needed amino acids. Non-ruminants must obtain essential amino acids directly from their diets.

Another uniqueness of rumens is that their microorganisms synthesize B-complex and K vitamins, negating the need to supplement these dietary needs in feed rations. The exception is sick animals in which rumen function is impaired.

Rumen inefficiencies
Carbohydrates in the cow's diet are degraded by microorganisms and fermentation into volatile fatty acids, methane and carbon dioxide. The volatile fatty acids are absorbed directly from the rumen into the animal's bloodstream.

Methane and carbon dioxide gases are expelled from the animal's body through belching, which has become a concern of the Environmental Protection Agency (EPA), some state regulatory bodies and animal rights groups.

Avery's opinion on animal eructation of carbon dioxide is, "If grassy areas aren't eaten by animals, the dry grass will ultimately be struck by lightning, ignite, and release fiery clouds of carbon dioxide."

Degradation products from protein in the rumen are ammonia and organic acids. Some of the ammonia is recombined into microbial protein, and some ammonia is absorbed across the rumen wall and excreted in the urine. This loss of ammonia is an inefficiency in the rumen digestive process.

Breaking down and reforming feedstuffs generates heat. This fermentation heat is a disadvantage to the animal in most instances. An exception is in cold climates when fermentation heat helps the animal meet its energy requirement.

A rumen is subject to bloat and acidosis that cause reduced performance and in some cases, death. Bloat occurs when fermentation gases are produced faster than they can be expelled by the animal. Acidosis is the result of excessive breakdown of readily available carbohydrates.

A ruminant has a unique digestive system that allows it to convert poor quality roughage into protein, energy, B-complex vitamins and vitamin K. The few inefficiencies in ruminant digestion can be managed in most cases by understanding the process and utilizing good animal husbandry practices. With the large amount of roughage in the world, cattle and other ruminants certainly play an important positive role in our environment.

Is the Cow's Digestive System Getting Proper Nutrition?

Using GAN Lab Analysis and NUTBAL to Fine-tune Your Herd's Nutrition Plan

Nutrition management is an effective and valuable method of ensuring herd health and efficiency. Proper utilization of feed becomes an increasingly important factor in times of stress such as ongoing drought or extreme temperatures.

Managing what type of forage or hay goes into your cattle is easily accomplished in a confined feeding operation. But what if those cattle are grazing pasture? One of the most important values in your herd's economic equation — dietary analysis — can quickly turn into guesswork.

However, even if you don't know exactly what is going into your animals, technology exists to help producers get an accurate picture of their herd's nutrition situation by taking a look at what's coming out.

The Grazingland Animal Nutrition Lab, or GAN Lab, can provide producers the critical time- and money-saving ability to know exactly what their cattle are getting — and, perhaps more importantly, needing — in their nutrition profile. Using near infrared reflectance spectroscopy (NIRS) technology to chemically analyze pasture-collected manure samples, GAN Lab is able to determine the nutritional quality of an animal's intake and assess a herd's nutritional well-being. This information, paired with a special computer software program that runs equations on the available information, can assist in developing the best plan for your operation, whether it's cow-calf, stocker or replacement heifers.

GAN Lab
The Ranching System Group of what is now the Department of Ecosystem Science and Management of Texas A&M University began work in 1997 on the technologies that are the foundation of the GAN Lab capabilities. Originally a research-based operation to study animal nutrition and grazing behavior, the lab focused on developing the means to monitor range conditions utilizing fecal profiling with NIRS technology.

While the lab's initial purpose was to develop a non-invasive tool for range research, the potential benefits to cattle producers became evident during ranch trials conducted in the early 1990s. These trials helped develop and test the first cattle equations and were published in 1992 by Drs. Jerry Stuth and Robert Lyons.

The success of these first equations led to the opening of the GAN Lab to offer their services to livestock managers nationwide. After the completion of the equations for cattle, the lab's research turned to developing diet quality equations for goats, white-tailed deer, sheep, elk and equines.

NIRS technology
The analysis of fecal samples has proven to be a useful and effective diagnostic and management tool. Samples collected in the pasture are sent to the GAN Lab, where chemical analysis is made to determine the quality of the forage the animals were consuming 36 hours prior.

The NIRS process involves exposing a dried, ground fecal sample to light energy. The intensity of the light energy's reflectance is measured across several hundred wavelengths in the near infrared band. Reflectance is influenced by number and type of chemical bonds in the feces. This measurement and analysis can accurately detail the percentage of protein and energy of the forage the animal was grazing.

The diet quality of concentrated feeds such as grain or liquid feed is not evaluated in the NIRS analyses. The impact of such supplements on animal performance is evaluated by the second component of the nutritional monitoring system, the Nutritional Balance Analyzer or NUTBAL.

NUTBAL software
With the results from the NIRS analysis, producers can utilize the Center for Natural Resource Information Technology's Nutritional Balance Analyzer (NUTBAL) program to craft a plan for optimized herd performance. NUTBAL, a computer software program, evaluates your herd's specific variables such as breed type, body condition, forage conditions, supplemental feed information, environmental conditions, performance targets and NIRS results to produce a report of the animal's protein and net energy use. This allows the producer to determine the best, and most likely cost-effective, feeding solutions for the herd.

Access to NUTBAL, which is free for the public to use, is available via an interactive website or to download and use on your own computer. The online application allows users to submit their information for NIRS analysis on a livestock fecal sample, which is then mailed to the GAN Lab. Once the GAN Lab completes and records the sample's NIR analysis, the interactive website automatically generates NUTBAL reports for the sample based on data entered by a user.

What can the NIRS/NUTBAL system do?
Supplements and stored forages represent a major expenditure in livestock production. The NIRS/NUTBAL system can become a valuable tool for producers, managers and consultants to make informed herd feeding and grazing decisions. The combined NIRS/NUTBAL system monitors changes in forage quality over time and matches the nutritional needs of livestock to the most economical feedstuff available. A regular monitoring program can alert producers to deficiencies that develop in field forage.

Reports can tell you the animal's positive or negative plane of nutrition, weight gain or loss, protein or energy performance, your most cost-effective supplement, the amount of feed needed and amount of forage consumed. You can also determine if there is enough forage to maintain a sufficient body condition score (BCS) for breeding, calving or wintering a herd.

Will this system work for other grazing animals?
GAN Lab's NIRS/NUTBAL system works just as well for sheep, goats and wildlife.

What sampling schedule should I follow?
Deciding how often you should sample, and when, depends on objectives and your budget. You can sample infrequently or throughout the year to monitor body condition. GAN Lab recommends an initial period of routine testing to establish a knowledge base of your herd's health, paired with spot testing after weather extremes or forage changes. More data points will allow you to make more precise goals. Also, different operation goals can dictate how often you sample.

The benefits of a year-round monitoring system include improving body condition more economically by recognizing problems in forage requirements and maintaining a proper weight during extreme situations such as drought, cold, heat, breeding season, calving and weaning.

The expected turnaround time for results and reports is 10 to 14 days from the date the samples are received at the lab.

Services
A basic service includes the NIRS analysis with crude protein and energy reports as well as the NUTBAL report of animal performance, feedstock quality and limiting growth factors.

For producers requiring more in-depth analysis and advice, a NUTBAL Advisory is available that includes NIRS fecal analysis and NUTBAL animal performance reports, and adds recommendations and goals for managing nutrition, written by a GAN Lab scientist. GAN Lab holds occasional producer-oriented workshops at Texas A&M University on operation of the NUTBAL software. For more information, visit their website at cnrit.tamu.edu/ganlab or call 254-774-6134.