All living organisms require specific essential nutrients to satisfy the biological processes associated with tissue maintenance and repair, for growth and for all other productive activities including reproduction, lactation or work. Unlike green plants, animals cannot capture solar energy and combine this with basic elements to provide nutrients but must rely on finding, ingesting and digesting suitable feeds to satisfy their requirements. Most potential feeds have complex chemical structures that must be broken down (digested) into simple compounds before they can be taken into (absorbed) and used within the animal body. This process includes the ingestion of feeds, the physical and chemical reduction to simple products for absorption from the digestive tract and the subsequent elimination of indigestible residues. Chemically, digestion involves a hydrolytic reaction splitting large molecules until they are reduced to very small components that can pass across the intestinal lining into the body. Combinations of voluntary and involuntary mechanisms under both neural and endocrine controls and with acceleration by enzyme catalysts regulate these processes.
Livestock are macrophageous animals ingesting pieces of plant or animal material and, once inside the alimentary tract, the complex feed is broken down by digestive processes for absorption into the body. Consuming stationary plants seems a relatively simple means of satisfying feed requirements but is in fact rather difficult since most animals cannot digest the complex cell walls. Feeding on animal tissue presents substantially fewer digestive challenges. Cells forming animal tissues contain nuclei and other organelles in a fluid or semi-fluid matrix (cytoplasm) bounded by a simple plasma membrane. After ingestion by another animal, this plasma membrane breaks easily, liberating glycogen, protein and other constituents for digestion by enzymes secreted from the lining of the digestive system.
Most plant cells, in addition to their cytoplasmic matrix with its associated organelles and plasma membranes, posses an exoskeleton to provide mechanical support (see following illustration). Carbon, transformed into organic form through photosynthesis, may be used immediately for metabolic needs, converted into structural material or stored as complex polysaccharides. Some of the energy reserve is conserved as starch in cereal grains, roots or tubers. Most of the carbohydrate must, however, be synthesized into the supporting tissues. These cell walls are composed of a cellulose fibre network in a gel like matrix of hemicellulose and lignin, with relative proportions shifting from the former to the latter as plants mature.
Digestion includes the ingestion of feeds, the physical and chemical reduction to simple products for absorption from the digestive tract and the subsequent elimination of indigestible residues. The processes involved are highly regulated by combinations of voluntary and involuntary mechanisms under both neural and endocrine control. Plant-consuming animals obtain energy from breaking down starch and cellulose. Although these two compounds differ only in bond linkages between glucose molecules, this seemingly small variation produces substantial differences in physical properties and suitability as components for inclusion in diets for particular animal species.
Animals are usually classified into two groups on the basis of their digestive physiology; ruminants and monogastric (or non-ruminants). This is really an over-simplification, since some non-ruminants, in addition to their simple stomachs, have an important symbiotic relationship with a microbial population in their hind-gut. Animals such as the horse and the rabbit are able to take advantage of the nutrients from many of the same feeds as ruminants. The major difference between these animals and ruminants is that their fermentation takes place at the end of the gastrointestinal tract while in the ruminant it occurs at the beginning. These non-ruminant herbivores also have requirements for dietary essential amino acids and vitamins, since although they are synthesized by the microbes, the animal's ability to absorb them from the large intestine is severely limited.
Canines and felines have simple stomachs, short intestinal tracts and undeveloped caeca. All ingested food passes quickly through the digestive system with little opportunity for microbial fermentation. Thus, these animals are carnivores, feeding almost entirely on animal tissue although some nutrients can also be obtained from high quality plant material like hulled grains or tubers that contain starch rather than cellulose. Omnivores, like humans or pigs, also possess simple stomachs but their digestive systems are capable of extracting nutrients from readily digested plant tissue if the plant cell wall is thin or the fibrous coat surrounding grain seeds or nuts is disrupted or removed. Omnivores vary considerably in ability to obtain nutrients from plant cell walls. In pigs, the sacculated colon and caecum make up about half of the total digestive capacity, providing substantial volume for microbial fermentation. This allows extensive break-down of complex plant tissues and liberation of sufficient nutrients from reasonable quality forages to satisfy maintenance requirements of mature pigs. In contrast, microbial fermentation is possible in only 17% of the human tract, severely limiting ability to digest fibre.
Some herbivores like cows, sheep, goats, buffaloes and deer, posses a complex fore-stomach (rumen, reticulum and omasum) populated by micro-organisms. This is a symbiotic relationship since the bacteria and protozoa inhabiting the rumen posses the enzymes necessary to ferment and break down cellulose, liberating volatile fatty acids fore absorption directly through the rumen wall and used as an energy source by the host. The micro-organisms also synthesize nutrients into their own tissues and, as their population increases, large numbers are flushed into the true stomach (abomasum) and intestines for digestion by the animal. Alternately, complex or protected proteins, peptides and even some carbohydrates may by-pass the rumen and escape fermentation. These pass directly into the abomasum and intestines to release nutrients through conventional mammalian digestion-absorption processes. Species with this modification are ruminants and can obtain all essential nutrients from plant cellulose. Non-ruminant herbivores such as equines, cameloids and rabbits can also derive substantial nutrients from plant materials. These animals have well developed caeca and large intestines that contain numerous symbiotic micro-organisms possessing the ability to ferment cellulose.
Ruminant Digestive System Ruminants, unlike most other mammals, do not have upper incisor teeth, but possess a tough dental pad on which the bottom incisors can put pressure. In cattle, the tongue is used to pull long feed into the mouth, while the lips are used when the animal is grazing or eating smaller feeds such as grains. Usually enough chewing occurs to mix the feed with saliva and form a bolus which may be swallowed. Domesticated ruminants produce large amounts of alkaline saliva, which contains a little amylase (an enzyme required for starch digestion). The saliva aids the chewing and swallowing of dry feeds, allows for breakdown of short chain triglycerides by salivary lipase, and buffers acids produced during rumen fermentation. The volume of saliva produced is affected by the form of the feed being consumed and the water intake of the animal.
The rapid movement of the bolus through the esophagus is probably due to the presence of striated muscle in the ruminant esophagus. Three sphincters are also present but they may be more important during regurgitation than in swallowing. The bolus is deposited into the anterior portion of the rumen or the area of the reticulo-rumen fold.
The ruminant stomach is divided into four compartments, the reticulum, rumen, omasum and abomasum. The reticulum and rumen are joined by a fold of tissue; the reticulo-rumen fold, with the result that digesta may move freely between the two compartments. The ruminant stomach contains a large microbial population that exists in a symbiotic (or mutually beneficial) relationship with the animal. The walls of the rumen are lined with epithelial cells which terminate in papillae (small, finger-like projections). These increase the surface area for absorption and for microbial contact with the ingesta. The rumen microflora ferment cellulose, liberating volatile fatty acids. These volatile fatty acids (mainly propionic, butyric and acetic acid) are absorbed directly through the wall and serve as the main energy source of ruminants.
Rumination, or cud chewing (the ability to do so being one of the characteristics of ruminants), is the regurgitation, chewing to reduce particle size and swallowing of rumen contents. More time is spent chewing and more saliva is secreted during rumination than when the animal is eating. Animals ruminate much more during the night than they do during the daylight. Contraction of the muscular pillars in the rumen and the reticulum produce rhythmic mixing and moving of the ingesta throughout the rumen and reticulum. In young ruminants the reticular or esophageal groove is a continuation of the esophagus which forms a tube to bypass the reticulo rumen. This allows milk to pass directly into the omasum and then to the abomasum where it may be easily digested.
The next compartment is the omasum whose interior is partially filled by a number of longitudinal folds or leaves. The spaces between the leaves are packed tightly with finely ground ingesta, giving the whole compartment a round, hard appearance. The function of the omasum has not been clearly defined, but it is thought that it may act as a filter through which water and fine particles may enter the abomasum, but coarse particles may not. It also absorbs water and some ions from the digesta.
The last stomach compartment is the abomasum, which is very similar in structure and function to the glandular stomach in non-ruminants. Acid and some digestive enzymes are added to the stomach contents as they are moved through by contractions of the muscular wall.
The acidic ingesta passes into the duodenum where it is mixed with bile and pancreatic secretions. There is little digestion of soluble carbohydrates and lipids since most have been destroyed in the rumen. The small intestine is very efficient in absorbing amino acids. The large intestine and caecum may be of lesser importance in the ruminant animal, since many of the nutrients were released from dietary plant fibers in the rumen. Absorption of water, minerals, some nitrogen, volatile fatty acid and carbohydrate occurs in this region.
The terminal end of the gastrointestinal tract is the rectum. Its function is involved with defecation or elimination of the materials remaining after passage through the digestive system.
Non-ruminant Herbivore Digestive Tract The digestive system of the non-ruminant herbivore such as the horse, rabbit and guinea pig combines features of both the ruminant and monogastric systems. The proximal part (stomach, small intestine) of the gastrointestinal tract is very similar to that of the monogastric. The digestion of the dietary fractions which would also be available to the monogastric (ie.. the non-structural carbohydrates such as starch, proteins, minerals and vitamins) takes place in the stomach and small intestine. The more fibrous part of the feed, which in some situations is the majority of the diet, is passed through the small intestine to the hindgut (caecum and colon) where it undergoes digestive processes similar to those occurring in the rumen. The bacteria which inhabit the caecum and colon of the horse are, in most cases, identical to those found in the rumen of cattle. The end products of bacterial fermentation are also very similar to those of the ruminant animal. Since the major site of bacterial fermentation in the hind-gut fermenters is distal to the small intestine the non-ruminant herbivore may not be as efficient in using fibrous foodstuffs as is the ruminant. Much of the bacterial protein and cell wall constituents which would be available to the ruminant are lost to the horse. There is absorption from the hind-gut of by-products of bacterial fermentation such as volatile fatty acids, free amino acids, B-vitamins and minerals released from plant sources, but losses of these nutrients in the feces is greater in the horse than in the cow. The rate of passage of ingesta through the gastrointestinal tract of the horse is, however, more rapid than in the ruminant. This allows the horse to meet a great part of its requirements from fibrous sources by ingesting large quantities, digesting what is available and eliminating the remainder from the tract relatively quickly. For horses with high nutrient requirements (ie.. pregnant, high performance and working horses) a diet with a high proportion of cereal grains and supplements is necessary to meet their nutrient requirements.
Monogastric Digestive Systems In animals like pigs, the lips, cheeks, palate and tongue are all involved with prehension and movement of feed in the mouth. Small feeds are usually ingested with the tongue, while the teeth shear off any large or long pieces. Pigs can also suck up slurry feeds and water. Saliva is produced by three primary glands, and its volume and consistency can change with the nature of the food. Once food has been chewed and mixed with saliva to a proper consistency it is swallowed and passed down the esophagus to the stomach. The motility of the stomach is necessary to mix the digesta with the gastric juices and to move the digesta into the small intestine.
The small intestine, comprised of the duodenum, jejunum and the ileum, is the site where the majority of digestion takes place and most, if not all, nutrient absorption occurs. The duodenum is the site for the mixing of digesta with intestinal, liver and pancreatic secretions. These secretions serve to buffer the contents as they leave the stomach, and to lubricate the bolus for ease of movement through the intestines.
The caecum and colon (hind gut) retrieve any nutrients, primarily water and electrolytes, remaining in the digesta as it leaves the small intestine. The caecum is a blind sac arising at the junction of the ileum and colon. Anaerobic fermentation of fiber in the caecum and colon produces some utilizable energy in the form of volatile fatty acids. The amount of energy produced is small in relation to the pig's total requirement but hind gut fermentation liberates substantial nutrients in horses and rabbits.
Go to Digestive Physiology of Herbivores, a site provided by Colorado State University, for more information.
Avian Digestive Tract The avian oesophagus has an outpocket, the crop, which occurs about two-thirds of the way down its length, right before it enters the thorax. There are large numbers of mucous glands above the crop which serve to augment the small amount of saliva produced. The crop functions mainly to store feed. From the oesophagus, the bolus moves into the proventriculus, where HCl and pepsinogen are produced (at higher levels per unit body weight than most mammals). The gizzard, a very hard, muscular organ is the site for grinding of the ingesta and also for much of the gastric digestion. Movement of ingesta is related to a coordinated effort of the crop, lower oesophagus and gizzard, with little muscular contraction of the proventriculus involved.
The level of fibre in broiler rations has an effect on the size of the proventriculus and gizzard. The more fibre, the slower the rate of passage through the proventriculus. Thus the amount of gastric juices produced is less, the more the gizzard must grind the feed, so the larger the gizzard. The gizzard further degrades the ingesta to prepare for digestion in the small intestine. The ingesta is mixed in the gizzard and when the particles are fine enough they are pushed out into the small intestine. Intestinal contents are continually refluxed back into the gizzard which differs from most animals since the pylorus effectively blocks back-flow of fluid from the small intestine into the stomach. Grit was thought to be necessary for the digestion of coarse feedstuffs, but there seems to be no advantage to adding grit to a mash diet.
The small intestine, about 125 cm long in a mature chicken, is made up of
the duodenum, jejunum and the ileum. The duodenum ends where the bile and
pancreatic ducts empty into the intestine. The jejunum and the ileum cannot be
readily differentiated. The large intestine absorbs some of the nutrients,
usually water and electrolytes, remaining in the digesta as it leaves the small
intestine. The colon in avian species is very short and the ceca are much
longer and are paired. Only fluids and very fine particles enter the ceca and
once they are evacuated from the ceca are rapidly excreted. Volatile fatty
acids are by-products of anaerobic fermentation of fibre in the ceca. Ducks and
geese have longer digestive tracts than do chickens. Thus, these species can be
productive on diets that are higher in fiber. The energy derived from volatile
fatty acid production is small compared to the chickens' total requirement but
can be substantial in ducks and geese. The colon acts more as a passage of
ileal and cecal digesta than as a fermenter or absorber. The cloaca is the
terminal end of the gastrointestinal urinary and reproductive systems. Voiding
moves feces and uric acid out of the cloaca together.
Check the Colorado State University site for additional information on avian digestion.
|Species||Small intestine||Caecum||Large intestine|
Other Major Organs of Digestion. The pancreas and liver are two other organs intimately associated with digestion. In addition to producing several hormones, the pancreas secretes a number of digestive enzymes (lipase, amylase, trypsinogen, chymotrypsinogon) that are essential for breaking down complex feed components and liberating the nutrients in forms that can be absorbed. The liver adds bile to the ingesta as it passes through the small intestines. The bile emulsifies fats so they become soluble and detoxifies potentially harmful materials that gain entrance to or are formed within the body.
Digestion and liberation of nutrients from animal tissues occurs quickly and efficiently during passage through the stomach and intestines. In contrast, digestion of complex plant tissue requires retention of ingested feeds for a considerable period under conditions suitable for microbial fermentation. The gastrointestinal anatomy and related ability to promote fermentation allow classification of animals into general groups as shown in the following table.
|Major fermentation site||Species|
| Pregastric fermenters
|multicompartment stomach, regurgitation||cattle, sheep, goats, buffalo, camel, deer|
|Nonruminants||multicompartment stomach, no regurgitation||hippo, hamster, kangaroo|
| Hindgut fermenters
|large caecum||rabbit, Guinea pig|
|Sacculated colon||prominent large intestine
|Unsacculated colon||no modifications
The breakdown of lignocellulose in the rumen and other parts of the digestive system is limited by the crystallinity of cellulose fibres and the barrier to microbial attack created by the lignin and other related components of the mature plant wall. Various fungi with high lignin degrading activity are currently under study to increase understanding of the physical and enzymatic mechanisms employed in these processes. On the basis of this knowledge, solid-substrate fermentation technologies have been developed and significant improvement of in vitro digestibility can now be achieved through use of fungi carefully selected for activity on particular substrate. A specific gene coding for lignin peroxidase has been isolated, cloned, incorporated into and expressed by bacteria, so genetic engineering to construct strains with increased in vitro lignin-degrading potential, and subsequent introduction of these into the rumen, may be feasible in the future.
Crude plant by-products are abundant throughout the world, with annual
production of cereal grain straw, corn stover and sugar cane tops and bagasse
each accounting for many millions of tonnes. However, since these all contain
high proportions of lignin protected hemicellulose, and cellulose,
digestibility is low even in ruminants. Considerable research is being
conducted on developing techniques that improve digestibility of low quality
roughage (grinding, chopping, pressure, explosion, irradiation, chemical
treatments, etc.) and successful methods to increase the digestibility would
contribute dramatically to better livestock nutrition.
Animals must receive sufficient amounts of all essential nutrients (water, energy, amino acids, vitamins, minerals) to remain healthy, to grow and to produce. Ration formulation involves combining the various ingredients so that an animal's nutritional requirements are met. Producers must always be aware that the nutritional requirements vary with species, age, production and even the season of the year. One of the major challenges facing the livestock production industry today is providing adequate amounts of a balanced ration at a reasonable cost.
Livestock feeds can be classified as roughages, cereals and supplements. Examine the individual components and mixed feeds to determine ingredients and which animal species might utilize these.
Roughages The roughage or forage utilized in Canada comes from native rangelands and pastures, improved pastures, crops harvested and stored specifically for feeding to animals or residues of crops grown for other purposes. Roughages are usually feeds that have a low bulk density, but because of the variety of crops which are considered to be roughages, there is a great deal of variation in composition. Most feeds in this group have a high crude fibre content and a low digestible energy content. Corn silage is one exception since, although it has high levels of crude fibre, it also has high levels of digestible energy. The protein, mineral and vitamin contents can vary substantially between roughages and also between crops of one roughage. Forages form the major part of most ruminant rations, since they are less expensive than other feeds and the ruminant animal is able to digest most plant components. However, some ruminants are fed very little roughage. Cattle and lambs being readied for market are often fed a ration based almost entirely on cereal grains. High producing dairy cows may also receive a very small roughage component in their diets.
Pasture or grazed forage is the most common roughage throughout Canada. All native and most cultivated pastures are composed of grass species alone or mixed with legumes and regional climate is the major consideration in deciding which types or combinations predominate. Temperate pastures can only be used as a feed source for a few months of the year, so forages must be harvested and stored as hay, haylage or silage to provide feed during the nongrowing seasons. Hay, haylage and green chop are all made from grasses or grass-legume mixtures. Common legumes include alfalfa, clover and trefoil and, compared to grasses, these have higher protein and calcium levels. With hay and haylage the goal in harvesting the plants is to optimize the yield, which increases with maturity, and also to maximize digestibility, which decreases rapidly with maturity. Forage quality is very dependent on the amount of moisture in the plant at harvest which affects the nutrient loss during storage. Green chop is a forage that is cut and chopped in the field and fed fresh to confined animals so it is available only during the active growing season.
The major advantage of haylage over hay is that making hay of good quality is very weather dependent. With the advent of in-barn hay dryers, this has been somewhat alleviated but the ensiling of haylage at higher moisture levels than possible with hay is still a very popular alternative. Hays are usually stored at 15-20% moisture, while haylages may range from 45-55% moisture. The ensiling process results in a decrease in protein N, and an increase in non-protein N. Since haylages are usually left in the field only long enough to wilt, their exposure to the sun is much shorter, and they usually contain less Vitamin D than dry hay. They store best, with the least spoilage, in oxygen-limiting tower silos. A wide variety of compounds, classed as nutrients, preservatives, fermentation aids or biological additives have been added to haylages in an effort to improve quality after ensiling. Differing results have been obtained but it seems as though some will improve quality.
Corn silage is a popular feed in areas where corn is grown specifically for livestock feed. It is very palatable with a fairly high level of digestible energy (although this can vary somewhat depending on the amount of grain or the maturity of plants at harvest), but reasonably low levels of protein, Ca and P. Urea, anhydrous ammonia, or other sources of N can be added to increase the level of crude protein. The plants are usually harvested and put directly into the silo at approximately 60-75% moisture. Silage may also be made from the other cereal grains which usually have higher protein but lower energy content than corn so animals must eat more to gain the same amount of weight.
Corn stover and straw are examples of crop residues that may be fed to ruminants or other herbivores. Corn stover is the stalks and leaves remaining in the fields after corn is combined for grain. Waste from canneries processing sweet corn, peas, bean and other vegetable crops, may be fed effectively as ensiled crops. Most crop residues are limited in availability to a short period after the primary crop is harvested.
Cereals Cereal grains contain substantial quantities of readily available carbohydrates, sugars, starches, fats or oils. They usually contain little fibre and are highly digestible, especially by monogastric animals, so form the major part of diets for animals with simple stomachs. Corn, wheat, oats and barley are the most common cereal grains fed in Ontario, and are generally less variable in nutrient composition than roughages. Corn has the lowest levels of protein, and is deficient in the essential amino acids lysine, tryptophan and methionine. Cereal grains are all low in Ca, and while the P level is quite high, most of it is in the form of phytic acid which is unavailable to monogastric species. Grains are stored generally at 10-15% moisture but high energy cost associated with drying has contributed to the current popularity of high moisture corn. This is stored at 22-30% moisture in oxygen-limiting, upright silos. Corn is usually infested with molds during the growing season and, under certain conditions, these organisms may produce mycotoxins that contaminate the grain and can produce disease when affected cereals are fed.
Soybeans are not generally considered cereal grains but whole beans can be fed to ruminant animals as both a protein and energy source. The protein level is 35-40% and although it is deficient in methionine it is not of much importance for ruminants. The raw beans possess a trypsin (an enzyme involved in protein degradation) inhibitor so they must be treated before they can be fed to monogastric species.
Supplements are feeds which are high in one or more of the nutrients required by animals (with the exception of water). They can be further broken down into protein supplements, energy supplements and vitamin and mineral supplements. Some feeds may fall into more than one category. Many of these feeds are by-products of industries that produce a product destined for human consumption.
Energy Supplements Many energy-rich feeds are by-products of cereal grain milling. These by-product feeds usually come from various layers of the seed covering, which, along with being higher in fibre, are higher in protein and minerals than the seed itself, which is mainly starch. The most common milling by-products are from wheat with lesser amounts derived from corn. These are classified on their fibre content and include bran, middlings, shorts, red dog and wheat-germ meal. In Ontario and Canada, poultry feed is the largest user of these by-products. While much of the starch has been removed, they are still good sources of energy.
Molasses is the major by-product of sugar production, coming mainly from sugar cane but also from sugar beets. Most molasses in commercial use is adjusted to contain 25% water. It may also be dried so that it may be added to dry diets, but this is a much more expensive product. While molasses is a good source of trace minerals, the protein and vitamin level is quite low. It is used often to stimulate eating, to reduce dustiness in feeds, as a pellet binder, and when fortified with an N source, as a ruminant feed known as a liquid protein supplement.
Beet pulp is another by-product of sugar extraction. It may be purchased either flaked or pelleted and may have molasses added to it. It is very palatable and, despite its relatively high fibre level, is quite digestible. It is often used in lactating cow rations to stimulate appetite.
Surplus fats may be fed as an energy source only, since they supply almost no protein, vitamins or minerals. When available at reasonable costs, fats may be used in feeds to decrease dustiness and increase palatability. Since fats are subject to oxidation and rancidity, which will decrease their palatability, antioxidants are usually added. Fats are not often fed to ruminant animals except perhaps in milk replacer formulas and occasionally in a finishing or lactating cow ration, since ruminants are not tolerant of fat levels higher than 7-8%.
Protein Supplements These may originate from either plant or animal sources, or in the case of ruminants, from non-protein N Sources. A protein supplement is a feed which has more than 20% crude protein. These are usually the most expensive constituents in animal rations so their selection is affected by cost and availability. The content and availability of amino acids for monogastric species, the presence of undesirable or toxic substances and the content of other nutrients should also be considered. Most of the plant protein-rich feeds are by-products of the oil extraction industry, with soybean meal being the most common in Ontario. The protein is usually low in the sulphur containing amino acids cysteine and methionine and may be low in lysine. Soybean meal has a protein level of 44% or 48% depending whether or not the hulls are added back. It is probably the most common protein source in North America and it is quite palatable, highly digestible and has fairly high energy levels.
Canola meal is probably the second most common oilseed meal fed in Ontario, and likely the most common in the Western provinces. It contains between 35% and 40% protein, with slightly less lysine and slightly more methionine than soybean meal. Perhaps the major disadvantages of canola meal are the high fibre levels and resulting lower energy levels for all species and the anti-nutritional factors which may be present. Canola has been bred to be low in the anti-nutritional factors that were previously associated with rapeseed, and most of the new varieties are "double-low". For most animals the best results in growth rate and feed efficiency are obtained when the level of canola meal in the diet is less than 20%.
Cottonseed meal and linseed meal are two other potential feedstuffs, but due to climate and changes in consumer preference very little is fed in Ontario. Linseed meal, often called oilcake, is a meal made from flax, which is deficient in lysine and is seldom grown in large quantities anymore. It is most popular as a feed for show cattle, since it tends to produce a very glossy hair coat, but it is generally too expensive for the protein it provides to be used commercially.
Other by-products of plant origin are brewer's and distiller's grains. Either can be purchased in the wet state, but since it is more convenient for transportation and storage, they are usually dehydrated. Distiller's dried grains contain 25-30% protein, have relatively high fibre levels and, due to the yeast present, a high B vitamin content. They are often deficient in lysine since they are primarily corn based. Brewer's dried grains have considerably more fibre (18-19%) and as a result are more suitable as a protein supplement for ruminants. The protein level is 25-30% and low in lysine, but high in methionine.
Animal protein supplements (meat meal, blood meal, bone meal) are usually by-products of the meat-packing industry. Since these are animal tissues, the amino acid distribution is usually similar to the animals' requirements, although quality may be quite variable since the composition of the meal may vary from batch to batch.
There are two major types of fishmeals - those made from the waste of fish caught for human consumption and those made from fish caught specifically for industrial use. Fish meal must be dried down to 15% moisture and have the fat content reduced to a maximum of 10%. Antioxidants are always added since the oil oxidizes readily. The protein is very digestible and is very high in lysine, which makes it a good protein source to supplement feed cereal grains. Fishmeal is a good source of the B vitamins, all minerals, and seems to have unidentified growth factors which enhance growth rate and feed conversion in swine.
Single cell protein. Certain bacteria, yeast, fungi and algae can ferment residues from pulp mills, food processing, alcohol production and even human or animal wastes. At the present time, harvesting and dehydration costs are uneconomical, but products resulting from this process can be fed to supply part of the protein requirement for almost all animals without any noticeable decrease in performance. The protein concentrations range from 48-80% and are reasonably well digested. Most contain moderate energy and may provide other nutrients such as the B vitamins. Perhaps as production techniques are refined, costs will decrease and these protein sources will become more competitive with other feedstuffs.
Numerous minerals are essential for proper animal nutrition. In addition to
their metabolic functions, the macro-minerals are necessary for tissue
structure (e.g. calcium and phosphorous in bone or egg shells) and for milk
secretion. Plant tissues obviously contain considerable mineral but the actual
content can vary with stage of maturity and soil conditions. Feed analysis is
necessary to indicate the actual composition so that diets can be fortified as
Bone meal, limestone and many mineral supplements are available from commercial feed suppliers. Analysis of home grown and purchased feed ingredients will reveal their actual composition. Once this information is available, informed decisions can be made on what additional ingredients will be necessary to balance the diet for various species and production stages.
Some farm animals certainly suffer from mineral deficiencies. However, excess amounts are toxic so conscientious attention to individual requirement and inclusion of the appropriate supplements is necessary to satisfy needs.
Vitamins function as cofactors or enzyme activators in metabolic processes so are necessary for all general body functions and maintenance of health. All green, growing plants contain carotene which animals can convert into vitamin A. Supplemental vitamin A may be necessary to ensure an adequate supply whenever herbivores are not grazing on good quality pasture and for omnivores and carnivores. The rumen micro-organisms produce B vitamins so these are unlikely to be deficient in matures ruminants. In contrast, diets for very young calves and all non-ruminants may require some supplementation with B vitamins. The sun's ultraviolet rays produce vitamin D from the provitamin in the skin and from ergosterol in plants during field curing of hay. Thus, animals spending considerable time outdoors or receiving ample, good quality hay should have sufficient. Animal diets usually contain sufficient vitamins E and K but deficiencies can occur. As with all other nutrients, diets should be designed to meet individual requirements and fortified to provide a slight excess of any vitamins that could be deficient under natural conditions.
Although often overlooked, water is a vital nutrient for all animals. Requirements vary with age, production and especially with the season of the year. An adequate supply of potable water is essential for all livestock production. If this is not assured throughout the year, seek another location!
Feed expenses constitute 50 to 80% of total production costs for most livestock products. Thus, anything that affects feed price or utilization will affect economic performance. Nutrients must be partitioned or applied to various functions within an animal's body and these follow priorities. The maintenance of vital body function is the number one priority and this must be satisfied fully before any other function ensues. Availability of excess nutrients beyond those requires for maintenance and for fighting disease, allows their use for production purposes that include growth, work and reproduction. Of these, growth of young and replacing body reserves in emaciated animals takes precedence. Finally, when everything else is satisfied, animals may reproduce.
Successful management involves manipulating facilities, feeds and animals so that a substantial proportion of provided nutrients can be used for production.
For most animal systems, the actual value of feed, either purchased or produced, constitutes 50 to 80% of the total cost of production. Thus, any reduction in the cost of the total ration or of individual ingredients could improve economic efficiency.
Amounts lost to rodents or birds, and through faulty equipment or even careless handling all contribute to feed wastage. These are often overlooked when feed prices are low but should be curtailed in all instances to insure maximum efficiency.
Nutrients must be used to support the bodily defence mechanisms to overcome diseases so they are not available for growth or production. Diseased animals may also have depressed appetites so feed intake will be reduced.
A dairy cow producing 6,000kg per lactation has the same maintenance requirements as a cow of similar body size that produces 12,000 kg. Provided their nutritional requirements are met and health needs satisfied, higher producing animals should be more profitable.
Improving the digestibility will enable animals to meet their needs for maintenance, growth and production with less total feed.
Growth or lactation efficiency
Obtain appropriate genotypes. Keeping animals in good health and providing adequate amounts of a balanced ration are essential if they are to express full genetic potential for production. Housing must prevent stress/distress.
Obtain the appropriate genotype, allow it to grow at the optimum rate and reach the market in top condition to get the best return.