Qualités Nutritionnelles du Bœuf

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.

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 (bacteria, protozoa and fungi) 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 again. 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.

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 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 carbohydrate sources differently, any 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 and are directly absorbed by the animal in the small intestine to supply nutrients for growth and reproduction.

Key Nutrients Required by Beef 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

Beef Cattle Energy Requirements

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. However, not all of this energy is available to the animal as losses occur through digestion and excreted as feces, urine, gases and heat.

• Digestible energy (DE) indicates 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.

Protein Requirements of Beef Cattle

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.

In cattle diets, protein is often expressed as crude protein (CP), which is determined by multiplying the nitrogen (N) content of the feed and forage by 6.25%.

The majority of the protein that ruminants ingest is broken down by the rumen microorganisms and resynthesized as microbial crude protein (MCP). Forages contain 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.

Urea is a common non-protein nitrogen (NPN) source for use in beef cattle rations. Ammonia toxicity is a concern when urea is included in the diet, but can be managed with proper dosage, use and mixing techniques.

• Non-protein nitrogen sources do not contain amino acids. Rumen microbes can convert the nitrogen to MCP if adequate energy is available in the diet. As rumen microbes breakdown NPN, they produce ammonia. If insufficient energy is available, the ammonia may be absorbed at levels too high to be broken down by the liver, resulting in toxicity.

• True protein 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 (VFAs). 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: microorganisms in the rumen combine the ammonia supplied by RDP or other non-protein sources (e.g. urea) with rumen digestible carbohydrates to synthesize microbial CP. MCP is digested in the abomasum, with the resultant amino acids absorbed in the small intestine.

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.

Beef Cattle Water Requirements

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 by beef cattle 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),
• 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.

Video: What’s in Your Water? Water Quality and Economics of Pump Systems

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.

Minerals Requirements of Beef Cattle

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)

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 available to the cattle may be much lower than anticipated because of these interactions. Therefore, even though mineral 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.

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 formulation 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 minerals 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 minerals 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 bioavailability 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.

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.

Cattle will often demonstrate a preference for certain mineral mixes or molasses lick tubs, which can create challenges in terms of daily intake when feeding free choice. While recommended mineral intake is about 60 grams (2 ounces) per head per day, when fed free choice some cattle will over-consume mineral, while others may avoid it altogether. Monitor the herd to determine which cattle are frequently at the mineral stations and which cattle may not be consuming adequate amounts. Some producers report better intake when they offer choices of different mineral mixes, such as loose and lick tubs. Others report that moving the mineral stations a little farther from water sources to encourage grazing on less utilized areas of pasture caused mineral consumption to drop off slightly. 

Ensure that there are enough stations for the number of cattle; a common recommendation is one mineral station for every 20-30 head. When feeding cows with calves at side, more stations may be necessary to ensure that the calves have access, as dominant, mature cows will often outcompete calves for mineral. When possible, work with a nutritionist to formulate an appropriate mineral blend for each operation.

In the following video from Beef Research School, Dr. John McKinnon explains what factors producers should consider when designing a mineral program. He also provides tips for achieving ideal consumption.

Video: Mineral Feeding – Why Should I Supplement?

Salt Requirements for Beef Cattle

Although the salt requirement for beef cattle is relatively low, cattle will seek out salt. Loose salt mixed into mineral blends can help increase intake to ensure adequate amounts are being consumed. Salt can also be used to encourage cattle to graze underutilized areas of pastures, by placing further away from water and areas where cattle tend to congregate.

Many producers choose an iodized salt block to ensure adequate iodine intake, especially in areas known to have iodine deficient soils. The normal requirement for iodine in a beef cattle diet is 0.5 ppm of the total diet and can usually be provided with iodized salt blocks. Additional iodine may be necessary if feeding cover crops such as brassicas including turnips, rapeseed or kale which contain compounds that inhibit iodine uptake from the gut. While higher cost, salt blocks that contain trace minerals such as copper, zinc, cobalt and selenium may be used for herds that have experienced problems with foot rot. While these salt blocks can supply small amounts of certain minerals, additional supplementation with loose or lick tub formulations may still be necessary to provide and maintain adequate mineral levels.  

Beef Cattle Vitamin Requirements

Vitamins support many vital metabolic processes in cattle. They are inorganic compounds that are required in small amounts. The age and production status of the animal will impact vitamin requirements. Vitamins A, D, E and K are fat soluble and are stored in the animal’s fat tissue and liver. Because of this, they do not need to be supplemented daily if the animal has adequate reserves. These vitamins are present in feed sources and are responsible for key metabolic processes within the animal, and thus are important to monitor to ensure deficiencies do not develop. Fresh, leafy forages generally contain adequate levels of vitamin A and E, however, drought, forage processing and extended storage periods can reduce levels. While supplementation of A, D, E and K may not be required during the summer months, supplementation is recommended during winter months, especially prior to calving. The main functions of vitamins A, D, E and K are:

Vitamin A – essential for bone, teeth and nerve development, eyesight, kidney function, and soft tissue maintenance. Vitamin A is often low in newborn calves, and young animals generally have smaller reserves than older animals. Deficiencies, which may manifest initially as rough hair coat, dull eyes, diarrhea and pneumonia, can progress and cause reduced bone development and density, decreased fertility, night blindness, reduced feed efficiency and increased susceptibility to disease. Cows with deficiencies may abort, have weak calves, or be difficult to settle. Recent research has shown a positive impact on calf performance when pregnant beef cows were supplemented with vitamin A during the third trimester.

Vitamin A is stored in the liver, but without an outside source, these liver stores will be depleted after two to three months. Carotene is converted to vitamin A from beta carotene, found in green forages and yellow corn,⁹ in the small intestine. Conditions that may require supplementation include periods of greater stress, such as weaning or transportation, feeding stored forages during winter that have reduced carotene levels, and feeds or water with higher nitrate levels.

Vitamin D – required for calcium and phosphorus metabolism, as well as teeth and bone development. It is synthesized by the sun or by eating sun cured forages. Early signs of deficiency include poor appetite, decreased growth in calves, weakness, stiff gait and laboured breathing. Soft bones, rickets, and swollen joints develop if deficiencies continue. Pregnant animals with a vitamin D deficiency may abort or have weak, deformed or stillborn calves.

Vitamin E – required for muscle development and occurs naturally in feedstuffs.

Vitamin K – required for blood clotting and is usually sufficient in green forages. Rumen bacteria generally make sufficient quantities of vitamin K from feed sources. Feeding some clovers, especially if mouldy, interferes with the production of vitamin K due to a compound called dicoumarol present in clover.

Vitamin C and the B vitamins (thiamin, niacin, choline) are water soluble. Calves receive vitamin B from milk, and once the rumen becomes functional, these vitamins are synthesized by rumen microorganisms and do not usually require supplementation unless energy and protein balance in the diet is not adequate⁶.

Feed Sources and Quality – Impact on Beef Cattle Nutrition

Beef cattle can utilize a wide variety of feedstuffs. However, different feeds have different benefits and limitations when it comes to supplying nutrients:

• forages – high in fibre, lower in energy, with varying protein content; examples are hay, grass, greenfeed, silage
• grains – high in energy and low in fibre, moderate to high protein content; examples are corn, oats, barley, wheat
• oilseeds – high in protein, high in energy, high in fat, variable fibre content; examples include soybeans, canola meal
• by-products – variable nutrient content, may be high moisture; examples are distillers’ grains, bakery waste, grain screenings, hulls

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. Forage quality directly impacts animal performance, growth, reproduction and profitability. 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. Harvesting and feeding high quality hay can reduce the amount of supplemental minerals and vitamins that may be required. 

The level of minerals in a forage will depend on many factors including soil type, plant species, stage of growth, the weather, and overall management of the stand. Maturity at harvest, as well as harvest techniques and storage will also impact forage quality. In addition, the absorption of trace minerals from forages in the gastrointestinal tract can be very low. As Dr. John McKinnon explains in this blog, antagonistic interactions between minerals can reduce levels absorbed even further, sometimes even to zero.  

Low quality forages generally reduce voluntary intake, which can result in protein and energy deficiencies. When high quality forage (vegetative growth) is consumed, dry matter intake tends to be 2.5-3.0% of live body weight. When forage is of lower quality, dry matter intake can drop closer to 1.8% of body weight, reducing protein, energy, and mineral consumed. In some instances, when the animal’s needs are not being met (e.g. feeding a ration containing very low-quality forages or straw during cold temperatures in winter), they may actually over-consume low quality feed, as they attempt to derive enough energy from the feed. This over-consumption of bulky, low quality feed can cause compaction. In this situation, feed is unable to move through the digestive tract and can cause death.

Analyzing feed samples will provide an indication of protein and energy levels available. While feeding lower quality feedstuffs can be an economical way to stretch feed supplies, producers must monitor consumption and animal condition to avoid potential issues with under or over consumption of low-quality feed. Use of tools such as the Winter Feed Cost Comparison calculator can assist producers with cost comparisons.

Knowledge of forage quality and animal requirements is necessary to formulate rations that will support and maintain a high plane of nutrition. While most producers recognize that grazing forages can provide an economical source of nutrition, the relationship between forage quality and profitability is often unappreciated. Producers must manage grazing in response to environmental conditions and pasture growth during the season to avoid either overgrazing, which reduces forage yield, and under grazing which can lower the overall forage quality due to over-mature vegetation and may also increase forage waste. Proper grazing management can support both nutrition and profitability.

Factors Affecting Beef Cattle Nutrient Requirements

Nutritional requirements of beef cattle are influenced by the stage of production. This production cycle, which is based upon a well-managed, healthy cow in good condition (Body Condition Score = 3) maximizes profitability by producing a calf every 365 days. The annual production cycle, based upon ideal length of time for each phase, includes:

• Calving, postpartum, early lactation (day 0 to day 82)
• Conception, early gestation, late lactation (day 83 to day 199)
• Mid gestation (day 200 to day 274)
• Late gestation, pre-partum (day 275 to day 365).

Phase 1 – begins at calving. This is the period of greatest nutritional demand for the cow. She must lactate, repair her reproductive tract, resume heat cycles, breed, and if she is a young cow, she must also continue growth and development. Her voluntary feed intake is highest at this point and as this blog explains, she requires a high energy and protein diet of at least 62% TDN and 11% CP. If she is not fed to meet nutritional needs, she will lose weight and may not rebreed.

Phase 2 – begins with conception. The cow is now supporting herself, her calf (through lactation) and her fetus. Nutritional demands are still high as she reaches peak lactation but are lowered by 8-13% compared to the first phase. Cows that produce more milk will have higher nutrient requirements. The fetus is small, and its growth is slow, but cows and heifers often lose weight during this time.

Phase 3 – is when the cow is in mid-gestation. Immediately after calves are weaned, nutritional needs are at their lowest due to the end of lactation. Energy and protein requirements drop by up to 35% when compared to the peak demand. Fetal growth remains slow, and voluntary feed intake is the lowest during this period. This is the best time to put weight back on cows to help them gain condition¹⁰. See the body condition  information to learn more about how to ensure beef cattle are in ideal condition.

Phase 4 – is the final phase prior to calving, and cows must be in good body condition to give birth to a healthy calf, produce milk and re-breed quickly. Energy and protein needs increase by 20% compared to mid-gestation. During this period, the fetus can gain up to 60 pounds and the placenta is growing as well. Nearly 75% of fetal growth occurs during this phase¹¹. Cows need to gain 0.5 kg (1 lb) to 0.68 kg (1.5 lbs) per day, while weight gain for heifers should target twice that amount. The cow has reduced rumen capacity due to the growth of the calf, so a reduction in feed intake usually occurs in the latter portion of this phase.

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.

Producers often divide the herd into different feeding groups to tailor the feeding program to provide an adequate level of nutrition. These groups may include:

Group 1 – Mature cows in good condition – Average quality hay supplemented with grain or pellets, minerals, fortified salt and vitamins, will generally meet the nutritional needs of this group.

Group 2 – Bred replacement heifers and second calf heifers – Young, growing animals do not compete effectively for feed with mature cows. Heifers require good quality hay, silage or alternative feeds, or grain to meet their needs for growth and development. These animals are still growing and gaining body weight, in addition to developing the fetus. These animals may benefit from organic (chelated) or hydroxy trace mineral supplements, which have greater bioavailability, to support growth and reproduction.

Group 3 – Thin, old cows – These cows will need extra energy, particularly during winter months. These cattle may benefit from additional vitamin and mineral programs to avoid deficiencies.

Group 4 – Yearling steers, bulls – Steers and bulls will require different feeding programs depending on their size and if they are on a maintenance program or are backgrounding or finishing.

If the ration is based on straw or low-quality hay, or if feed intake is limited, it is even more important to separate the herd into different feeding groups to match the nutritional needs of each group. Use feed testing and ration-balancing software like CowBytes to determine the appropriate ration and amounts of feed for each group.

Maintaining Cattle Nutrient Requirements 

Cattle require energy, protein, water, vitamins and minerals in adequate amounts for optimal nutrition. The requirements for these nutrients will vary depending upon the class, age, condition, and stage of production of the animal. Environmental factors will also influence animal nutrition and nutrient levels both in the feed and water sources. Feed costs represent the greatest expense associated with beef production. Nutrition is the most important factor for cow fertility, which is a main driver of profitability. Supplemental vitamin and mineral programs can improve livestock health, immune function, performance and fertility.

Each operation is unique; work with a nutritionist to identify and correct nutritional deficiencies early, before herd health and profitability is compromised. Identify groups of cattle that may require additional or customized feeding strategies. Feeding only low-quality feedstuffs to save feed costs will generally increase reproductive losses, unless offset by what is likely to be a more expensive supplementation program. A properly balanced ration will improve cattle performance, productivity and ultimately profitability.

Definitions

Acid detergent fibre (ADF) – a chemical analysis that estimates the total fibre (including indigestible lignin) in the feed. A high ADF indicates reduced digestibility and likely lower voluntary feed intake.

Amino acids – nitrogen-containing molecules that are the building blocks used to create protein in the body.

Available protein – the portion of crude protein that can be digested by the animal. It represents the proportion of total protein after deducting the ADF-N fraction of a feed.

Carbohydrate – a source of dietary energy that includes starches, sugars, pectins, cellulose and hemicellulose. All carbohydrates contain carbon, hydrogen and oxygen, and are usually divided into two types: structural (fibre from plant wall) and non-structural (sugars and starches from plant cell contents).

Cellulose – a fibrous carbohydrate that is the main part of plant cell walls.

Chelated mineral – a chemical bond formed between an organic molecule and a mineral that increases mineral bioavailability to the animal and can reduce excretion of excess minerals in manure.

Crude protein (CP) – an estimate of the total protein content of a feed determined by analyzing the nitrogen content of the feed and multiplying the result by 6.25. Crude protein includes true protein and non-protein nitrogen sources such as ammonia, amino acids and nitrates.

Digestible energy (DE) – the apparent energy that is available to the animal by digestion, measured as the difference between gross energy content of a feed and the energy contained in the animal’s feces.

Fat soluble vitamins – stored in the animal’s fat reserves or liver, including A, D, E, and K.

Hemicellulose – a carbohydrate found in plant cell walls that is more complex in structure than sugars but less complex than cellulose.

International unit (IU) – a standard unit of potency of a biological agent, such as a vitamin, hormone, vaccine, or antibiotic.

Neutral detergent fibre (NDF) – an insoluble fraction containing all plant cell wall components left after boiling a feed sample in a neutral detergent solution. A high NDF indicates lower digestibility and voluntary feed intake.

Non-protein nitrogen (NPN) – urea and ammonia are compounds that can be used by the microorganisms in the rumen to form true protein, that can then be converted to meat or milk by the animals. When feeding low quality, low protein feeds, urea can help the ruminal bacteria to create true protein.

Non-structural carbohydrate – comprised of sugar, starch and pectin, this is the non-NDF fraction of feedstuffs.

Rumen degradable protein (RDP) – the portion of dietary protein that is degraded in the rumen. It feeds the rumen bacteria, supplying microbial protein.

Rumen undegraded protein (RUP) – the portion of dietary protein that escapes degradation by ruminal microorganisms and passes into the small intestine where it is digested and absorbed.

Structural carbohydrate – the fibrous, cell wall or support structure of the plant, containing cellulose, hemicellulose and lignin.

Water soluble vitamins – include the B complex vitamins and vitamin C. They are generally not supplemented to cattle after two months of age, due to the ability of rumen microbes to manufacture them in adequate amounts¹².

References

1.	Hamilton, T. 2015. Basic Beef Cattle Nutrition. Ontario Ministry of Agriculture.
2.	Meat and Livestock Australia Limited. 2006. Beef Cattle Nutrition.
3.	Guyer, P.Q. 1976. Use of Energy Values in Ration Formulation. G76-321. University of Nebraska.
4.	Parish, J.A. 2008. Protein in Beef Cattle Diets. The Beef Site.
5.	Alberta Ministry of Agriculture. 2005. Water Requirements for Livestock.
6.	Rasby, R.J., A.L. Berger, D.E. Bauer, and D.R. Brink. 2011. Minerals and Vitamins for Beef Cows. University of Nebraska.
7.	McKinnon, J. 2017. More Questions on Mineral Nutrition. Canadian Cattlemen Magazine.
8.	Drovers. 2011. When to Use Chelated Trace Minerals.
9.	Bailey, E. 2017. University of Missouri Extension. Vitamins for Beef Cattle.
10.	Hall, J.B. 2009. Nutrition and Feeding of the Cow-Calf Herd:Production Cycle Nutrition and Nutrient Requirements of Cows, Pregnant Heifers and Bulls. Virginia Cooperative Extension, Virginia Tech, Virginia State University.
11.	The Cattle Site. 2013. The Annual Production Cycle. www.thecattlesite.com.
12.	Ontario Ministry of Agriculture, Food and Rural Affairs. 2012. Definitions of Feed Manufacturing and Livestock Nutrition Terms.

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