Beef cattle nutrition is paramount for productivity, influencing the animal's phenotype through the interaction of genetics and environment. Nutrition significantly contributes to the environmental component, substantially affecting the animal's observable traits. To thrive and be productive, beef cattle require a balanced intake of water, energy, protein, minerals, and vitamins. Understanding and meeting these dietary requirements are crucial for growth, development, reproduction, and overall health.
The Importance of Beef in Global Human Nutrition
Beef plays a significant role in global human nutrition, standing as the third most consumed meat worldwide, following poultry and pork. Per capita consumption is approximately 6.4 kg for beef, 14.0 kg for poultry, and 12.2 kg for pork. Beef consumption is steadily increasing, driven by population growth and rising household incomes. Estimates suggest that by 2027, beef consumption will rise by 8% in developed countries and 21% in developing countries compared to the 2015-2017 average.
Beef is a nutrient-dense food, offering essential macro- and micronutrients beneficial for human health. A 100g serving of beef provides over 25% of the Recommended Dietary Intake (RDI) of protein, niacin, vitamin B6, vitamin B12, zinc, and selenium, and over 10% RDI of phosphorus, iron, and riboflavin. Beef protein is characterized by its complete amino acid profile, containing all essential amino acids. Additionally, beef provides antioxidants such as carnosine and anserine.
Australian Beef Industry
Australia is a major player in the global meat industry, ranking seventh in world beef production and third in beef exports in 2018, with 1.5 million tons of carcass weight equivalents (CWE). The beef cattle industry contributes significantly to the Australian economy, accounting for 20% ($12.1 billion) of the 2016-2017 total gross value of farm production and 22% of the total value of export income. The Australian beef cattle population is approximately 23 million head, occupying about half of Australian farms and 75% of the total agricultural land mass.
Half of the national beef cattle herd is located in northern Australia, with 43% in Queensland and 16% in Western Australia and Northern Territory. Queensland alone accounted for 1.1% of the global beef herd in 2017 and 8% of world beef exports in 2016. The predominant breeds in northern Australia, including Brahman, Santa Gertrudis, and Droughtmaster, are bred for tick resistance and heat tolerance, which influences their meat characteristics compared to temperate breeds.
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To enhance productivity and meat characteristics, these breeds are sometimes crossed with Bos taurus, maintaining at least 5/8 Bos indicus genetic composition for adequate heat tolerance and tick resistance. Several composite breeds, such as Belmont Red, NAPCO Composite, and AACO, have been developed by crossing Brahman with British, European, and African breeds. However, low pasture quality and quantity remain a major limitation to beef production. Nutritional supplementation, particularly with Desmanthus, an environmentally well-adapted and vigorous tropical legume, has the potential to improve animal performance and meat characteristics.
Key Factors Influencing Meat Quality
Meat characteristics encompass the acceptability of a meat product in terms of color, intramuscular fat content, fatty acid (FA) composition, tenderness, juiciness, flavor, and aroma. Market demands for meat products with healthy nutritional attributes and sensory characteristics significantly influence consumer willingness to pay. Consumer taste panel assessments have demonstrated a negative impact of Bos indicus content on meat characteristics such as tenderness, marbling, and juiciness.
The FA composition of ruminant muscle tissues is crucial for meat-eating characteristics, influencing flavor and tenderness, and is controlled by genetic factors related to lipid synthesis and metabolism. Omega-3 long-chain polyunsaturated fatty acids (n-3 LC-PUFA) are beneficial for human health, improving brain and retinal development, maternal and offspring health, cognitive function, and psychological status. Enzymes like Delta-5 (Δ5), Δ6, and Δ9 desaturases play essential roles in polyunsaturated fatty acids (PUFA) metabolism and are influenced by dietary fatty acids and tissue type.
Fatty acid binding proteins (FABPs) are intracellular lipid-binding proteins that reversibly bind FA and other lipids. Fatty acid binding protein 4 (FABP4) is expressed in adipose tissue and plays a vital role in lipid metabolism and homeostasis, interacting with peroxisome proliferator-activated receptors and binding to hormone-sensitive lipase. FABP4 is a candidate gene affecting intramuscular fat deposition, with associations to fatness traits in cattle varying across studies. Other genetic determinants of meat characteristics include the stearoyl-coA desaturase (SCD) and fatty acid synthase (FASN) genes.
The Role of Tropical Pasture Grazing Systems
Beef production in northern Australia relies heavily on extensive tropical pasture grazing systems, mainly native pastures dominated by C4 grasses. These pastures are primarily unimproved, with limited use of exotic pasture species in some regions of Queensland. Black Speargrass (Heteropogon contortus) and Aristida-Bothriochloa grasslands dominate the more productive areas of eastern Queensland. In northern and western Queensland, Northern Territory, and Western Australia, Mitchell grass (Astrebla spp.), perennial tallgrass and shortgrass grass species, and spinifex (Triodia spp.) are predominant. Stylosanthes legumes are widely sown across northern Australia’s light-textured soils to enhance pasture nutritive value.
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Clay soils, common in northern Australia pasture land, support pastures such as Asterbla spp (Mitchell grasses) and Iseilema spp (Flinders grasses), with few sown pastures like Cenchrus ciliaris (Buffel grass) in the Brigalow belt. Native pastures, except for young leaves and seeds, have relatively low nutritional value at the end of the summer growing season. During winter, growth is limited by temperature, and most native pastures are susceptible to frost, leading to a rapid decline in nutrient value.
Pastures are highly seasonal, with growth occurring during the wet season (November to April) and ceasing for 4 to 7 months of the year due to dry or cold conditions. During the transition from the rainy to dry season, pastures decline in leaf to stem ratio, with over 50% loss in leaf mass, crude protein content dropping below 8%, and an increase in dead material, reducing their nutritional benefit and palatability to cattle. Pastures also deteriorate after several years of grazing due to nitrogen run-down stress. This poor nutrition results in poor reproductive performance, slow growth rate, loss of body condition, increased susceptibility to parasites and diseases, increased turn-off age, and increased enteric methane emissions.
Forage quality is determined by nutrient concentration, intake, nutrient availability, and partitioning of metabolized products within animals. Low-quality forages contain less than 10% soluble sugars and starches, crude protein below 8%, and digestibility less than 55%. Utilization of these forages is limited by low intake due to physical fill limits and slow digestion resulting from high cell wall content and minimal nutrients to support efficient rumen microbial growth.
Adaptive Mechanisms of Beef Cattle to Undernutrition
Beef cattle utilize evolutionary adaptation mechanisms, both short-term (days), medium-term (weeks), and long-term, to cope with periods of undernutrition. Short-term underfeeding leads to a decrease in liveweight (LW) due to gut-fill variation, amounting to 4-5 kg LW/kg decrease in dry matter (DM) intake. Digesta in the reticulo-rumen of a fed ruminant animal can weigh up to 15% of body weight. Medium-term undernutrition results in organ and tissue mass variation, with liver and digesta-free gastrointestinal track reduction of more than 50% reported after three weeks of restricted dietary access.
Mid- and long-term weight losses are due to decreases in portal and hepatic blood flows, as well as mobilization of fat, muscle, and bone tissues in the reverse order of their deposition. The latest maturing tissues are more sensitive due to physiological priority. Storage triglycerides in the adipose tissue are hydrolyzed to release fatty acids (FA), which are oxidized directly to energy and broken down into ketone bodies in the liver. The liver also incorporates FA into lipoproteins and triacylglycerols in the blood. Ketone bodies, lipoproteins, and triacylglycerols act as sources of energy in peripheral tissues.
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Mobilized FA from the adipose tissue results in elevation of blood non-esterified fatty acids (NEFA). The liver removes 10% of NEFA from the blood during each cycle pass and converts half of all NEFA into ketone bodies. During undernutrition, gluconeogenesis from propionate decreases due to reduced propionate availability, partially compensated by gluconeogenesis from amino acid (AA) proteolysis, glycerol lipolysis, and lactate recycling. These metabolic changes are controlled by teleophoretic hormones such as insulin, glucagon, and norepinephrine, resulting in reduced energy expenditure. Mid-term experiments have shown that portal-drained viscera, liver, and skeletal muscles contribute significantly to changes in energy expenditure.
The Role of Nutritional Supplementation
High feed conversion efficiencies and medium to high levels of production can be achieved by ruminants fed poor-quality tropical forages adequately supplemented with critical nutrients. Metabolizable energy utilization efficiency of a forage can exceed that of grain-based diets when supplemented appropriately. Supplements optimize the availability of nutrients for rumen fermentative digestion and the utilization of fermentation products. Supplements with a high proportion of rumen degradable protein favor nitrogen recycling and promote increased microbial protein synthesis in beef cattle.
Supplementation of the drinking water of steers fed Pangola grass (Digitaria eriantha) hay with Spirulina has been found to increase ammonia-N concentration, propionate, and branched-chain fatty acids in the rumen fluid, although it may not always positively affect steer liveweight gains. Supplements are reported to stimulate feed intake and liveweight gain, achieving up to one kg daily. Supplementing cattle with urea together with molasses or other readily available energy sources at 2.8% N increases forage intake and prevents liveweight loss. However, the cost of supplementation during grazing in an extensive grazing system is a limiting factor, hence it is mainly used for weaners and the breeding herd.
Nutritional Management in Beef Cow Production
Profitable cow-calf operations manage their herds to calve early in a short calving season, requiring cows to conceive within 85 days of calving to maintain a 365-day calving interval. The postpartum period of anestrus varies among cows, but most research estimates that cows do not cycle for six weeks post-calving on average, leaving roughly two estrous cycles for rebreeding. Body nutrient reserves at calving and energy balance between calving and breeding affect when a beef cow will be ready to breed again.
Postpartum interval is longer in thin cows (BCS = 4) than cows in moderate condition (BCS 5-6). Body condition scoring is a subjective process, and it may be more useful to identify cows as thin, moderate, and fleshy at calving, separating thin cows and providing a higher quality diet. Allowing the forage base to absorb increases in nutrient requirements is essential for beef cows, reducing the need for purchased feedstuffs. A beef cow production cycle can be broken down into four phases based on nutrient requirements: postpartum/pre-pregnancy, gestating and lactating, gestation, and pre-calving, with peak nutrient requirements coinciding with the postpartum/pre-pregnancy phase.
Optimizing Calving Seasons and Forage Utilization
Aligning calving with the fall regrowth in cool-season pastures may be more reasonable than aligning with the spring flush of forage. Fall calving coincides with the fall flush of fescue growth, providing quality grazeable forage through peak nutrient requirements of early lactation and into the early part of the breeding season. Troubleshooting losses in body condition involves identifying the limiting nutrient, which is often overall feed availability rather than a nutrient concentration deficiency.
Many farmers stock farms based on a desired number of cows rather than the carrying capacity of the land. Hay production and feeding have become standard practices, despite significant costs. When forage quality is lacking, many producers supplement protein, but in cool-season forage systems, energy is often the limiting nutrient. Energy supplementation to beef cows is difficult because of the need to supplement energy daily. If body condition score (BCS) is declining, ensure that the cattle have enough to eat.
When the average forage height across a pasture is less than 4 inches, forage intake is likely limited. Be conservative in estimates and intervene by rotating pasture or providing supplemental forages. The Noble Foundation in Oklahoma uses rules of thumb for estimating the TDN requirement of beef cows: 55% TDN for pregnant cows, 60% TDN for late-gestation cows, and 65% TDN for lactating cows.
Supplement Strategies
In a scenario where forage quantity is limiting, managing supplemental forage is critical to keep feed costs from spiraling out of control. Feeding stored forages daily can reduce waste. A good rule of thumb is that a 1,000 lb bale of hay will provide a day's worth of feed for 30 cows. When working through a hay feeding budget, plan for roughly 33 lb of hay per cow per day. If energy is the limiting nutrient and forage intake is not limiting, start supplementation at 0.5% of body weight, fed daily. In cases where forage crude protein is well below 7% or if cows are consuming dormant warm-season forages, provide 1 lb of crude protein per cow per day.
Protein does not need to be supplemented daily to be effective. When purchasing supplements, price them per pound of nutrient required. Stockpiled tall fescue is an excellent feed source, grown on-farm with minimal input. With good yearlong planning and grazing management, stockpiled tall fescue can serve as an excellent winter feeding program. The nutrient profile of stockpiled tall fescue is outstanding and, when forage intake is not limiting, will meet the nutrient requirements of even lactating beef cows.
Understanding Nutrient Requirements
Beef cattle productivity is highly dependent on nutrition and the ability of the animal's diet to meet nutrient requirements. Beef cattle have quantified dietary requirements for water, energy, protein, minerals, and vitamins. A deficiency in any of these can affect the growth, development, reproduction, and health of beef cattle. Cattle require certain absolute amounts of nutrients, so even if a feed or supplement contains a relatively high amount of a nutrient, its ability to meet requirements depends on the amount consumed.
The amounts of nutrients that cattle require are influenced by various animal-related factors and environmental conditions, including weight, age, stage and extent of production, body composition, genetics, amount of physical activity, temperature, humidity, windchill, ultraviolet radiation, precipitation, and mud. Water is the most important nutrient to cattle, and a deficiency will result in dehydration and reduced productivity.
Protein Digestion and Utilization
Proteins are large chemical units made up of hundreds of amino acids, containing carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur. Animals require amino acids for the synthesis of muscles, blood proteins, and other body components. Ruminants can utilize both dietary protein and microbial protein synthesized in the rumen. It is essential to understand protein digestion and absorption in ruminants.
Rumen degradable protein (RDP) is the feed protein fraction degraded in the rumen, while undegradable protein (RUP) escapes rumen degradation and is digested and absorbed in the small intestine. Ensuring optimal rumen function includes meeting the animal’s RDP requirement.
Energy Requirements
Energy is required for various bodily functions, including maintenance, temperature regulation, reproduction, digestion, and waste elimination. Energy requirements increase with age, weight, stage of production, and environmental conditions. Lactation is the most nutritionally stressful activity for the cow, requiring nearly twice the daily protein of dry cows.