Karen Hoffman, USDA Natural Resources Conservation Service
Adapted with permission from: Mendenhall, K. (ed.) 2009. The organic dairy handbook: a comprehensive guide for the transition and beyond. Northeast Organic Farming Association of New York, Inc., Cobleskill, NY. (Available online at: https://www.nofany.org/files/TheOrganicDairyHandbook-2009_copy.pdf, verified 21 Nov 2019).
It is important to understand basic dairy cow physiology to grasp the concepts related to nutrition and ration formulation. The dairy cow is a ruminant and, unlike simple stomached animals (such as humans, pigs and horses), the cow has a complex stomach composed of four compartments: the rumen, the reticulum, the omasum and the abomasum (see Figure 1). It is this complexity that allows the cow to consume large quantities of plant-based material and convert this otherwise indigestible matter into high quality food for human consumption.
The rumen is a unique feature to ruminant species. It is the largest of all the digestive compartments with an estimated capacity of over 60 gallons. The rumen--often referred to as a large fermentation vat--is home to literally trillions of microorganisms (including bacteria, protozoa and fungi) responsible for the anaerobic digestion of forages; there are over 150 billion microorganisms per teaspoon of rumen fluid. Soon after the cow swallows a bolus of grass, microbes in the rumen begin to ferment the plant material, breaking down the more complex carbohydrates found in the plant cell wall including cellulose, hemi-cellulose, and lignin. Without the microbes, this process would not be possible due to a lack of appropriate enzymes. These microbes function best in a rather narrow pH range of 6.0 to 6.4. Care should be taken with supplemental feeds that may alter rumen pH, thus creating a problem for the cow metabolically speaking.
The other compartments of the stomach serve different physiological functions. The omasum is referred to as "manyplies" due to a number of layers or folds of tissue that work to grind the feed particles down into smaller pieces and absorb water. The abomasum is known as the "true stomach" since it functions much like the simple-stomached animals (pigs, horses, humans). This compartment releases stomach acids and enzymes that further digest plant material as well as breaking down microbes that are passing through the system to the small intestine.
The rumen’s large capacity allows the cow to consume large quantities of forages, the actual amount of dry matter (DM) consumed is highly influenced by forage quality. In addition to this massive rumen, the cow is also designed to spend a great deal of time (8 hours per day) ruminating, which amounts to a four-step process that includes re-gurgitation, re-mastication, re-salivation and re-swallowing, to enhance digestion. While this may seem redundant, rumination reduces the particle size (increases surface area), which enhances digestibility, in addition to creating a more favorable rumen pH due to the additional saliva.
Figure 1. Digestive anatomy of a cow. Source: Padgam, J. (ed). 2006. Organic Dairy Farming: A Resource for Farmers. Orang-utan Press.
Nutritional Concepts and Terminology
The concepts of nutrition for organic animals are not significantly different from conventional animals, but some of the nutritional challenges are. Organic animals, whether in the barn in winter or on pasture in summer, still require protein, energy, fiber, minerals, and vitamins. They still require a certain level of dry matter intake based on body weight, growth, or production, and should receive the nutrients needed to meet their requirements.
The following terminology may help introduce or act as a reminder of basic nutritional concepts.
Water is the most important of all nutrients for the dairy cow. Realizing that milk is 87% water, cows need an ample supply to stay fully hydrated and milking optimally. It has been reported that providing cows with extra watering locations during the heat of the summer can increase milk production by 2 to 3 pounds. The typical lactating cow will consume 4 to 4.5 pounds of water for every pound of milk production.
This is a primary nutrient needed for growth and production. Proteins are various combinations of amino acids and peptides and are major sources of nitrogen. There are different types of proteins classified by how the ruminant animal utilizes them. It is not necessary to add supplemental protein sources to a grain mix when cow as are grazing well-managed pastures although it is sometimes provided when pasture quality drops. Feeds high in protein include grass- and legume-based crops and certain grain crops such as soybeans or sunflowers (see Table 3 in "Nutritional Requirements and Rations").
This is the total protein in a feed or forage, including all the different protein fractions. It is calculated by determining the amount of nitrogen (N) in the feed and multiplying it by 6.25, because there are 16 grams of nitrogen in 100 grams of protein (100/16 = 6.25). The term “crude” reflects that it also includes some nonprotein nitrogen (NPN), so it is usually slightly inaccurate. Crude protein (CP) = amount of N in feed x 6.25.
Bypass protein is also called “undegradable protein” or “rumen undegraded protein” (RUP). This protein cannot be broken down to basic peptides or amino acids by microorganisms in the rumen (rumen bugs). It bypasses digestion in the rumen, but the animal uses it once it reaches the enzymes and acids in the lower gut or abomasum. In general, RUP should make up 40% of the crude protein portion of rations for milking cows.
This is also known as “rumen degradable protein” (RDP), and is the opposite of bypass protein. Rumen bugs break it down into peptides and amino acids and also use some of it to reproduce. When digested feed moves out of the rumen, some bugs go along as well. Without their ability to reproduce, the rumen would quickly lose function. The degradable protein is incorporated into the rumen bugs for the animal to use in the abomasum and intestines (lower gut) as well.
This is the most confusing term in protein nutrition, as it is part of the degradable protein. Soluble protein is easily dissolved and quickly used in the rumen by the rumen bugs. It includes some nonprotein nitrogen that moves into the liquid and includes sources like urea, naturally found in some feeds. Many fermented feeds have a high soluble protein level because fermentation can create or transform proteins into a soluble form. Rations for milking cows should target 30% soluble protein in the diet.
Energy is essential for growth and development. All living animals require five to six times more energy on a daily basis than they do protein. Energy is not easily measured and therefore is estimated from other components of the feed such as fiber levels and digestibility. Common terms are based upon the net energy system, and other terms include total digestible energy (TDN), metabolizable energy (ME), and digestible energy (DE).
The Net Energy system (NEM, NEG, NEL) describes the amount of energy the animal uses (or nets) for different functions. The NEL requirement tells us how much of the energy consumed is needed or utilized for lactation. This value for milking cows includes maintenance and growth requirements. NEG and NEM are values for growth and maintenance used primarily with growing or mature dry cows.
Total Digestible Nutrients (TDN)
TDN is not used to balance energy requirements, but is a method to compare feed quality, as it is a measure of feed energy content. A high TDN value indicates that the nutrients in the feed are highly digestible, enabling the animal to derive a higher energy value from the feed. A low TDN value indicates low energy feed that the animal will not utilize as well.
Relative Feed Value
This is also used to compare feed quality, but not specifically energy. A relative feed value (RFV) of 100 is the standard and reflects the quality of alfalfa hay with 41% ADF and 53% NDF (see below for definitions). The higher the RFV, the better the forage.
The fiber fraction of plants has three main compounds and they are all part of the plant cell wall that surrounds the fluid part of each cell. These fiber compounds are cellulose, hemicellulose, and lignin, all intertwined and complexed together in the cell wall. Cellulose is a straight chain of sugar molecules, and easily broken down by rumen bugs. Hemicellulose is also a chain of sugar molecules, but has branches along the chain. Lignin is a mostly indigestible compound—it goes through the animal virtually unchanged. Pectin and other organic acids are also part of the cell wall but are not considered to be a component of the fiber.
Acid detergent fiber (ADF)
ADF is the cellulose and lignin, as determined by a chemical procedure that washes away all the other plant components, leaving these fiber components intact. The ADF value estimates the energy content of feeds—the lower the ADF value, the higher the energy.
Neutral detergent fiber (NDF)
NDF is cellulose, lignin, and hemicellulose. The NDF value predicts intake and if NDF is low, animals are able to consume more feed.
Protein can be found in both forages and grains. See Table 1 for typical protein hay crop forages and their protein levels. Relying on high-quality forage helps to reduce or eliminate the need to purchase expensive organic protein sources.
Grain sources of protein include soybean meal and soybean by-products such as extruded, roasted, or expelled soy, distillers and brewers grains, canola meal, flaxseed meal, sunflower meal, field peas, corn gluten meal or feed, and peanut meal. Many of these may not be available certified organic in your area, so check their availability first. Organic protein grain sources are usually expensive. For this reason, growing your own high protein forage supply is worth considering to minimize the amount you need to purchase.
Forages are also sources of energy, and are included in Table 1. Corn silage provides energy through both the grain and stover, as the rumen bacteria can easily digest the fiber in the stover. Ruminal digestion of fiber produces chemical by-products called Volatile Fatty Acids (VFAs), acetic, propionic, and butyric acids. The animal derives energy from VFAs, and pasture and high-quality hay crops provide more energy to the animal via high digestible fiber. Some alternative forage crops such as sorghum-sudangrass, small grain silages, and brassicas are high in energy due to low fiber values and higher fiber digestibility.
Grain energy sources (corn, barley, oats, wheat, and cereal grains like spelt) have high carbohydrate levels. These grains are typically less expensive than protein sources, but are still expensive and suggest that high-quality forages are important for profitability. These grains have high levels of sugars and starches, frequently referred to as either Nonfiber Carbohydrates (NFC) or Nonstructural Carbohydrates (NSC).
|Goals for Forage Quality Parameters|
|Forage||% NDF (Fiber)||% Protein||NEL, Mcal/lb. (Energy)||% NFC (Carbs)||% ADF (Fiber)|
|Dry hay (grass)/mixed legume||50-60||13-18||0.52-0.61||15-20||35-42|
|Dry hay (alfalfa)||42-47||20-22||0.55-0.58||22-25||33-35|
haylage or baleage
|Alfalfa haylage/ |
|Managed pasture: |
spring & fal
|Managed pasture: |
Vitamins and Minerals
Farmers often overlook this nutrient class because traditionally they have used a standardized premix from a feed company to supplement vitamins and minerals. Oftentimes, these premixes provide more minerals than needed, and conversely, animals sometimes become mineral deficient if not enough attention is paid to the mineral program. In an organic dairy, minerals are important to maintain healthy animals. A mineral imbalance, either in excess or in deficit, will weaken the immune system contributing to other health problems.
Requirements include calcium, phosphorus, magnesium, potassium, sodium, chlorine, and sulfur. They all play key roles in various metabolic processes, as well as in the structure and function of different tissues and body fluids.
Trace minerals include cobalt, copper, iodine, iron, zinc, manganese, molybdenum, boron and selenium, and are important for the function of enzymes and hormones in the body. Since they support immune function, an imbalance could have a negative health impact.
Vitamins A, D, and E are important for immune cell function and many metabolic pathways. The precursor of Vitamin A is ß-carotene, which is plentiful in the green chlorophyll of fresh pasture, and the skin synthesizes Vitamin D when exposed to sunlight. During the grazing season a reduction in vitamin supplementation may be appropriate (except for Vitamin E, which needs to be supplemented year-round), but vitamins should be increased upon returning to winter confinement feeding.
Before feeding any mineral or vitamin, check with your certifier to be sure it is approved for use under organic regulations. Do not accept the word of a salesperson, as the list of approved supplements is constantly changing and different certifying agencies accept different supplements. Salt, a required mineral, is a good example as it must be from a naturally mined source and only a few companies make an approved product.
Some organic dairy farmers feed molasses as their only energy source, and it is gaining in popularity. Although there is little published research on feeding high levels of molasses, some farmers have found that it works well. Molasses has a broad range of 14 types of sugars including glucose, sucrose, fructans, xylotol, etc. The rumen bacteria can quickly utilize these sugars because they do not need to break them down through fermentation. Recent on-farm and laboratory research has shown that molasses is equivalent to corn meal in energy content (Soder et al., 2012), so if molasses is priced lower than other energy sources it is an economical alternative. Some farmers have tried feeding molasses as the only energy source without much success, thus molasses should substitute for a fraction of your normal grain amount rather than all of it.
In addition to high energy values, molasses contains a broad range of minerals. Molasses has a high potassium content, which may be a concern for dry cows moving into postcalving time. It also contains calcium, magnesium, copper, iron, manganese, and zinc. The minerals in molasses are highly concentrated so a relatively small amount may meet the animal’s requirements. It is low in phosphorus, so you may need to supplement additional P.
This ingredient provides a broad range of vitamins and minerals and is used by many organic dairy producers. Many farmers feed kelp free choice and animals usually eat it readily. Initially, they consume large quantities but later drop their intake once they adjust to eating it and their body has met any nutrient or mineral needs that were previously deficient. The minerals in kelp are chelated, making them more available to the animal. It also has a high iodine content, which may cause concern for nutritionists not familiar with kelp. This, however, does not seem to cause any problems.
Cows can also derive energy from fat sources. Roasted soybeans, whole cottonseed, canola seeds, and whole sunflower seeds are good sources of natural fat. Most of the conventional sources of fat, such as tallow and commercial by-pass fat, are not approved for organic use.
Importance of Fiber
Fiber is critically important to maintain a healthy rumen and in turn the health of the animal. Ruminants evolved with a rumen to digest fiber and have formed a long-term symbiotic relationship with the bacteria and other microorganisms within the rumen. Any time there is a shortage of fiber in the diet, the delicate balance of rumen bugs to cow health can easily be undone through too much acid formation, not enough buffering via cud chewing, and unhealthy shifts in the types of rumen bugs. Fiber digestion also allows lactating cows to produce higher butterfat levels, adding to the farm’s bottom line.
Pushing for extremely high levels of milk production has sharply increased the amount of grain fed to cows, disrupting rumen health and compromising this basic principle. In organic production, you need to optimize fiber in the diet to maintain healthy cows, a fundamental tenet to success, so cows stay in the herd longer. Forages are the main fiber source for dairy animals. While pasture is a source of good-quality fiber, it is fairly low, and you may need to include other ingredients like rolled barley or oats (hulls on), soyhulls, whole cottonseed, wheat midds, and citrus or beet pulp to increase fiber in the diet. Although these ingredients are not forages, when included at a low rate they add digestible fiber when needed and maintain butterfat. These may or may not be available as certified organic. (All components of the ration, including agriculturally-produced carriers in feed supplements, must be certified organic in order to be fed to organic dairy stock.)
Also in This Series
This article is part of a series discussing organic dairy nutrition. For more information, see the following articles.
- An Introduction to Nutritional Concepts and Terminology
- Identifying Nutritional Goals
- Nutritional Requirements and Rations
- Forage Testing and Interpreting Lab Analyses
- Managing Seasonal Diet Shifts
- Assessing the Feeding Program
References and Citations
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