As ruminant animals, cattle have a digestive system that allows them to digest roughage, like hay and grass, and concentrates such as barley grain or dry distillers’ grains, through the action of a diverse microbial community in the rumen. Cattle require energy, protein, water, vitamins and minerals in suitable amounts to provide adequate nutrition. Requirements will differ depending on the animal’s class, age, condition, and stage of production¹. Feed costs, including both grazed and conserved feed, are the greatest expense associated with beef cattle operations. Since nutrition is often the most important factor influencing reproductive performance, managing feed resources at a reasonable cost to consistently achieve high reproductive rates will help ensure profitability for beef cattle operations. In the backgrounding and feedlot sectors, feed costs and feed conversion efficiency significantly impact profitability. Across all sectors of the beef cattle industry, feed quality, cost, and efficient digestion/absorption/conversion are key factors in animal health, reproduction, performance and profitability.

On this Page

• Key Points
• The Ruminant Digestive System
• Key Nutrients Required by Cattle
  • Energy
  • Protein
  • Water
  • Minerals
  • Salt
  • Vitamins
• Feed Sources and Quality - Impact on Nutrition
• Factors Affecting Nutrient Requirements
• Conclusion
• Definitions

Key Points Gradual diet changes (over two to three weeks) are necessary to allow the rumen microbial population to adjust to changes in the diet Young, actively growing forages and legume blends can often meet the nutritional requirements for normal growth and maintenance of cattle herds.  Mature pastures, crop residues, or other low-quality forages may have reduced nutritive value, requiring supplementation of protein, energy or additional vitamins and minerals to maintain optimal health Energy is necessary for maintenance (feed digestion, core body functions, and activity requirements) and to support growth, lactation and reproduction. It accounts for the largest proportion of feed costs and is the nutrient required by cattle in the largest amount Neutral detergent fibre (NDF) and acid detergent fibre (ADF) are indicators of the amount of fibre in a forage. Higher values indicate poorer digestibility and voluntary intake may be reduced Protein is required for maintenance, growth, lactation and reproduction. It is a component of muscles, the nervous system and connective tissue Water is an essential nutrient for cattle, accounting for between 50 and 80 % of an animal’s live weight. Insufficient water intake reduces animal performance faster and more dramatically than any other nutrient deficiency At least seventeen minerals are required by beef cattle and are divided into two groups: macrominerals and microminerals Although minerals are required in small amounts for optimum beef cattle health, a deficiency can cause significant reductions in growth, immune function and reproduction Mineral needs will vary between herds based on many factors, including water and feed sources, stress, animal type and stage of production. There is no “one size fits all” mineral type or program Mineral toxicity may be indicated by decreased animal performance, anorexia, weight loss and diarrhea Vitamins support many vital metabolic processes in cattle Forage is an economical source of nutrients; however, feed quality and mineral content can vary widely, so feed testing and appropriate supplementation may be necessary to meet nutritional requirements Most forage species have the highest quality at the vegetative stage, when leaves are lush and green, and stems are young and supple. At this stage, these forages may be able to supply most of the nutrition that the cattle require Knowledge of forage quality and animal requirements is necessary to formulate rations that will support and maintain a high plane of nutrition Nutritional requirements of beef cattle are influenced by the stage of production

 

The Ruminant Digestive System

Ruminant animals have a complex digestive system with a four-chambered stomach. Each chamber (reticulum, rumen, omasum and abomasum) plays a role in digesting livestock feeds. Microorganisms colonize the reticulum and rumen (often collectively termed the reticulo-rumen) and allow cattle to digest feedstuffs high in fibre, such as grasses, straw and other forages. Balancing the requirements of the rumen microorganisms and the animal is essential for animal performance.

Cattle take large bites of feed and swallow with little chewing. Afterwards, they regurgitate masses of feed back up the esophagus and into their mouths, where it is chewed into smaller pieces and swallowed. This process is known as rumination or chewing cud. Between 60 to 70% of digestion occurs in the reticulo-rumen, which acts like a fermentation vat where bacteria and protozoa convert most of the plant fibre and carbohydrates to acetic, propionic or butyric acid (short chain fatty acids) and convert much of the ingested protein to microbial protein. The short chain fatty acids are absorbed through the reticulo-rumen wall and are used as energy in body tissues. Some of the sugar, starch and pectin may pass through the rumen and are then digested in the abomasum and small intestine.

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Microbes in the rumen require an anaerobic (oxygen free) environment with a slightly acidic pH range (6.5 - 7.0), a supply of protein (or non-protein nitrogen) and carbohydrates to feed the microbial population². The type of feed influences growth of the bacteria. Different rumen microbes prefer different types of carbohydrates (starch, cellulose, hemicellulose, starch, and pectin) and will increase or decrease in number depending upon the ratio of different carbohydrates within the diet. Because the various bacteria and protozoa digest cellulose, hemicellulose and starch differently, sudden changes to cattle diets can affect rumen activity. For example, a rapid change to a high energy diet with more grain can result in digestive disorders such as bloat and acidosis. Long periods of acidosis can also damage the rumen wall, potentially allowing bacteria to colonize the liver, causing abscesses³. For these reasons, gradual changes (over two to three weeks) are necessary to allow the rumen microbial population to adjust to changes in the diet. Nutrients that are not used for the microbes’ growth pass out of the reticulo-rumen to supply nutrients for the animal’s growth and reproduction.

Key Nutrients Required by Cattle

Young, actively growing forages and legume blends can often meet the nutritional requirements for normal growth and maintenance of cattle herds. Mature pastures, crop residues, or other low-quality forages may have reduced nutritive value, requiring supplementation of protein, energy or additional vitamins and minerals to maintain optimal health. Certain nutrients are required in the daily ration, while others can be manufactured and stored in the body.

Cattle require five key nutrients:

• energy
• protein
• water
• minerals
• vitamins

Energy

Energy is necessary for maintenance (feed digestion, core body functions, and activity requirements) and to support growth, lactation, and reproduction^1. It accounts for the largest proportion of feed costs and is the nutrient required by cattle in the largest amount. The components of feed that determine its energy content include carbohydrates, fats and proteins. On a feed test, energy content is usually expressed as total digestible nutrients (TDN); however, more precise terms such as metabolizable energy (ME) or net energy (NE) for maintenance (NE_m) or production (NE_g) may be preferred by nutritionists. These terms better reflect the amount of energy from feed that contributes to animal productivity. Energy deficiency caused by low intake or poor feed quality will limit growth, decrease milk production, reduce body condition, and (depending on timing and duration) may have negative consequences for reproduction.

Gross energy (GE) is the total amount of energy in the feed. But not all this energy is available to the animal. Feed energy is lost as it passes through the animal and is excreted as feces, urine, various gases, and heat. These losses are a normal consequence of feed digestion and the amount of energy lost at each step differs based on the quality of the feed. Digestible energy (DE) provides an indication of the portion of energy that the animal can digest, with the help of the rumen microbes. Metabolizable energy (ME) is the amount of energy available to the animal for metabolism and body functions after losses in energy from rumen fermentation (carbon dioxide, methane) and urine have been accounted for. Net energy (NE) is the amount that is available to the animal to maintain itself, grow, produce milk and reproduce.

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Neutral Detergent Fibre (NDF, %) indicates the amount of fibre content in the plant. High levels of NDF (above 70%) will restrict animal intake. More mature forages will have higher NDF levels. Acid Detergent Fibre (ADF, %) measures the least digestible portions of the forage plants, such as cellulose and lignin. High ADF indicates poor digestibility of the feed. High quality legumes generally have ADF values between 20-35%, while grasses can range from 30-45%.

Neutral detergent fibre (NDF) and acid detergent fibre (ADF) are indicators of the amount of fibre in a forage. Higher values indicate poorer digestibility and voluntary intake may be reduced.

NDF is a measure of the “bulkiness” of the diet and is mainly hemicellulose, cellulose, and lignin but due to limitations in the analysis it also includes a portion of the protein and insoluble ash in the plant. When NDF increases, animals consume less. ADF measures cellulose and lignin and is an indication of digestibility and energy intake. When plants mature, lignin content increases, resulting in higher ADF and reduced digestibility. Feeds high in ADF are less digestible than those high in starches and sugars. The starches and sugars in feed are classified as non-structural carbohydrates (NSC). Even in forages, NSC are an important source of energy.

Protein

Protein is required for maintenance, growth, lactation and reproduction. It is a component of muscles, the nervous system and connective tissue¹. Protein requirements depend on cattle age, growth rate, pregnancy and lactation status. Young, growing cattle, as well as those in late pregnancy or lactation, have increased protein requirements.

Most protein that ruminants ingest is broken down by the rumen microorganisms and resynthesized as microbial protein. Forages contain crude protein (CP) in two forms. The greatest portion of protein in forage is referred to as true protein, but forages also contain low amounts of non-protein nitrogen (NPN), which rumen microbes can use to synthesize microbial protein.

True protein in forages can be further classified as rumen undegradable protein (RUP or rumen bypass protein) and rumen degradable protein (RDP). RUP are peptides and amino acids that are digested in the abomasum and absorbed in the small intestine, while RDP is degraded or broken down by the microbial population in the rumen into ammonia and volatile fatty acids. Microorganisms in the rumen combine the ammonia supplied by RDP or other non-protein nitrogen sources (e.g. urea) with rumen digestible carbohydrates to synthesize microbial crude protein (MCP). MCP is digested in the abomasum, with the resultant amino acids absorbed in the small intestine. The amount of protein that reaches the small intestine depends upon the availability of RDP and the rumen digestible carbohydrate. If energy is deficient in the diet, surplus ammonia is converted to urea in the liver and then lost through urine. If protein is deficient in the diet, digestibility of fibre decreases due to diminished microbial activity and muscle will be degraded to meet the animal’s requirements for amino acids for core body functions.

Microbial protein makes up close to 70% of all protein absorbed from the small intestine and the protein contributions from microbes may be close to 100% for cattle fed low-quality forage.

In most cow-calf diets, forages with adequate digestibility will provide enough MCP to meet the cows’ requirements. But, for animals with higher protein demands, like growing calves or lactating cows, it can be beneficial to feed proteins that bypass the rumen and are absorbed in the small intestine, improving protein bioavailability. Extra protein can be provided by feeds that are high in RUP, like alfalfa dehydrated pellets, distillers’ grains, or alternative feeds like canola meal. Most forages have higher levels of RDP, particularly legumes.

During summer months, while forages and legumes are actively growing, they may supply up to 20% crude protein (CP) with a high level of RDP, but during the winter, protein levels drop off dramatically. Native pasture, for example, may test as low as 3-7% CP. Putting up good quality feed is key to supplying the beef herd with adequate quality forage sources through the winter⁴.

Water

Water is an essential nutrient for cattle, accounting for between 50 and 80 percent of an animal’s live weight. Insufficient water intake reduces animal performance faster and more dramatically than any other nutrient deficiency. For livestock to maximize feed intake and production, they require daily access to palatable water of adequate quality and quantity. Factors that determine water consumption include air and water temperature, humidity, moisture content of the feed/forage, cattle type (calf, yearling, bull, cow), the physiological state of the animal (gestation, maintenance, growing, lactating) and water quality.

Total dissolved solids (TDS) is the main indicator of water quality and is a measure of dissolved inorganic salts in water. TDS is impacted by high or low pH levels, sulphates, nitrates, salinity, excessive mineral levels, algae and bacteria. Testing water sources to ensure that cattle have access to adequate amounts of quality water is important.

The four main functions of water in the body are:

• to help eliminate waste products of digestion and metabolism
• a major component of secretions (milk, saliva) as well as individual and fetal growth
• as an aid in body’s thermoregulation processes through evaporation of water/sweat from the skin’s surface and respiratory tract
• to regulate blood pressure⁵

Read more about water requirements for beef cattle here.

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Minerals

At least seventeen minerals are required by beef cattle and are divided into two groups: macrominerals and microminerals. Macrominerals are those required in relatively large amounts for bodily functions, while micro or trace minerals are required in much smaller amounts.

The seven macrominerals required by cattle are calcium (Ca), magnesium (Mg), phosphorus (P), potassium (K), sodium (Na), chlorine (Cl) and sulphur (S). Macrominerals are required in amounts over 100 parts per million (ppm) and are often expressed on a percent (%) dry matter (DM) basis of the animal’s diet. 

Beef cattle require ten microminerals, also referred to as trace minerals. These microminerals, required in relatively small amounts are usually expressed in parts per million, (ppm) or mg/kg, rather than as a percentage of the diet. They are chromium (Cr), cobalt (Co), copper (Cu), iodine (I), iron (Fe), manganese (Mn), selenium (Se), and zinc (Zn).

Producers strive to provide adequate levels of macro and microminerals without over-supplementing, which increases costs, can create nutritional antagonisms, and increases potential for mineral loss through manure and urine⁶.

Minerals are required for several functions:

• skeletal development, bone, tooth formation and maintenance (includes Ca, P, Mg, Cr)
• energy, growth, immunity, and reproduction (includes P, Cu, Zn, Mn, Se)
• milk production (includes Ca and P)
• nervous system function and carbohydrate metabolism (Mg, K, Na, Cl, S, Co, I, Fe)

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Although minerals are required in relatively small amounts for optimum beef cattle health, a deficiency can cause significant reductions in growth, immune function and reproduction. The concentration of individual minerals in forages varies greatly depending on soil, plant, and management factors. It is important to include mineral analysis of forages as part of regular feed testing. There are also several interactions that can occur between minerals, vitamins and water or feed sources that can limit availability or absorption. As a result, the minerals that are actually available to the cattle may be much lower than anticipated because of these interactions. Even though concentrations found in forages may appear to be sufficient, availability to the animal may be significantly less. This can cause deficiencies which may not be noticed by producers until a significant reproductive or health issue arises.

In this blog, a Saskatchewan producer explains the problems that he experienced with copper deficiency.

Dr. Cheryl Waldner, NSERC/BCRC Industrial Research Chair in One Health and Production-Limiting Diseases, and Professor at the Western College of Veterinary Medicine explains that first and second calf heifers are most likely to exhibit signs of copper deficiency, such as lower conception rates. The cost of open cattle can quickly impact profitability. Waldner suggests that a properly balanced, palatable mineral mix be offered year-round to ensure optimal herd health and fertility.  Recent research in Saskatchewan revealed that forages sampled in spring and fall contained inadequate levels of copper and zinc for beef cows and growing calves in all soil zones. Additionally, up to 43% of the cows involved in the study were deficient in copper. Producers may notice some early signs of copper deficiency manifesting as a brownish or reddish tinge in black haired cattle.

Other problems that can arise due to mineral deficiencies include grass and winter tetany, white muscle disease, weak bones, hairless calves, goiter, scours, foot rot, retained placentas, low weaning weights, and reduced fertility.

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Trace mineral supplements are divided into three groups: inorganic, organic and hydroxy trace minerals.

Inorganic minerals are bonded to an inorganic molecule such as sulphate or oxide. They are usually less expensive but often have more variability in formulations and are less bioavailable. Inorganic minerals are often a first choice for producers due to affordability but may sacrifice availability and absorption. The absorption of inorganic mineral from the gastrointestinal tract can be less than five percent⁷.  In certain instances, such as with copper, inorganic minerals may be more prone to antagonisms with other minerals⁸. Simply feeding more inorganic mineral to offset these potential issues will not be successful and may cause more problems if levels of particular minerals become too high.

• Organic (chelated) minerals are bonded to a carbon containing molecule. These are usually more expensive but have improved absorption and availability to the animal. Producers generally use chelated minerals if mineral antagonisms exist in their area, such as high molybdenum or sulphur, which reduces copper availability. Chelated minerals are also used when animals are stressed, such as during weaning, or to ensure a high nutritional plane for procedures such as synchronization or artificial insemination on heifers.

• Hydroxy trace minerals have a crystalline structure that protects metal ions and allows trace minerals to bypass rumen digestion, thereby increasing bioavailability. Often available at a mid-range price, they are being utilized by some producers for cattle in high stress situations, such as weaning or artificial insemination.

With improved trace mineral absorption, producers report heavier weaning weights, increased average daily gain, improved reproductive efficiency, improved calving outcomes, and fewer health problems. Some also report reduced incidence of pinkeye, foot rot, scours and respiratory problems.

Mineral needs will vary between herds based on many factors, including water and feed sources, stress, animal type and stage of production. There is no “one size fits all” mineral type or program. Many mineral mixtures are available on the market, from loose mineral that can be offered free choice or mixed into a ration, to various molasses-based lick tubs that contain vitamins, minerals, and often some protein.

When rations contain grass hay, alfalfa, or a mixture of the two, calcium and phosphorus usually need to be supplemented in a 1:1 ratio (one part calcium to one part phosphorus). When feeding cereal forage rations, such as oat or barley greenfeed, a 2:1 or even 3:1 mineral mixture may be required to provide a balanced mineral mixture. Be sure to consult with a nutritionist to ensure proper supplementation.

Producers must monitor animals for signs of deficiencies or potential toxicity, and work with their veterinarian and nutritionist to ensure adequate levels and to correct any issues. Mineral toxicity may be indicated by decreased animal performance, anorexia, weight loss and diarrhea. It can lead to urinary calculi from excess phosphorus or inadequate calcium to phosphorus ratio, grass tetany from excess potassium leading to reduced absorption of magnesium, and polioencephalomalacia from excess sulphur. Some minerals such as copper, can become “tied up” or bound to other minerals present in feed and water. In these instances, the mineral will not be available to the cattle in the amounts required. If producers are using feed tests to balance mineral needs, animals may still be deficient due to reduced bioavailability.

An animal’s diet or ration will determine the type of mineral mix required to meet animal requirements. Grass is often low in calcium, phosphorus, magnesium and sodium, while alfalfa or other legumes are generally higher in calcium.

The following label contains the breakdown of a loose mineral that would be considered a 3:1 calcium to phosphorus ratio and may be used by producers feeding cereal greenfeed forages.

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Vitamins

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Producers often modify their feeding strategies during the annual production cycle of the beef cow to align with her energy and protein needs as she moves through the cycle. For example, lower quality feeds such as straw reduce costs during Phase 3, when the cow’s nutritional requirements are at her lowest. In Phase 4, as the rumen has less room for feed due to the growing fetus, she will benefit from higher quality feed such as good quality alfalfa hay or some grain to provide extra energy. A common rule of thumb is 55-60-65% for total digestible nutrients (TDN) and 7-9-11% for crude protein (CP) for mid gestation, late gestation, and lactation. More information on nutritional requirements can be can be found here. 

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