Proteins and amino acids

All living organisms, from viruses to man, require protein for structural units and for metabolically active compounds called enzymes. Proteins are made up of amino acids that are linked together in specific arrangements; each particular sequence creating unique 2- and 3-dimensional structures, as required for the proper function of the protein.

Amino acids are simple organic compounds that contain a central carbon to which is attached a carboxyl group (COOH), a nitrogen group (NH₃), and a side chain of varying complexity. The side chains determine the amino acid's identity. Amino acids link together by way of peptide bonds, which result when the carboxyl group of one amino acid bonds to the nitrogen group of another. The side chains are then free to act singly or in concert to perform whatever duty is required. This simple scheme results in a myriad of biologically active structures that can perform any number of tasks. The amazing array of functions performed by proteins includes muscle contraction, nucleic acid synthesis (DNA and RNA polymerases), deactivation of antigens (immunoglobulins), collection and processing of light (sight), and formation of various functional structures required for other life processes.

While several hundred amino acids exist in nature, only 20 to 25 are found in plant and animal protein. Most non-ruminant animals require 10 "essential" amino acids in the diet because they are unable to synthesize them. These include phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, arginine, lysine, and leucine (Just remember PVT. TIM HALL). Essential amino acids must ultimately come from plants that are consumed earlier in the food chain. Additionally, as discussed in a previous paper, taurine, which is a sulfur containing amino acid, is essential to strict carnivores. The other dozen or so AAs can be synthesized by animals from other compounds and from essential amino acids derived from the diet.

In the past, animal diets have been formulated based on "crude protein" (CP) levels. Swine diets, for example, typically should contain about 21% CP for pigs at weaning while about 14% CP is adequate for adult swine. Protein requirements are greater during the young and growing stages as one might expect, due to increased needs as the animal assimilates more tissue mass. Weaned dogs generally require 18 to 20% CP and cats about 35% CP in order to meet their needs, based on typical daily intake. While it is important that the proper amount of protein be included in any diet, of greater importance is the balance of various amino acids that make up the dietary protein. Amino acid balance is known as protein "quality" and the required quality differs among the species being fed. Protein quality is important because animals and man require amino acids in a balanced ratio in order that all appropriate proteins can be synthesized. Additionally, during metabolic processes, concentrations of substrates and intermediates, including amino acids, must be appropriate to drive the reactions in the proper direction. Traditional protein sources used in farm animal diets include soybean meal, alfalfa meal, and other easily accessible proteins. These sources, when combined with corn or wheat proteins (those grains are generally included as an energy source), usually have the appropriate quality for the intended animals and thus, based on their use, diets can be formulated on a CP basis with little regard for amino acid ratios. However, as we design diets for other species and/or use nontraditional or synthetic foodstuffs we need to define protein requirements based on amino acid needs rather than a CP basis. In the swine diets mentioned above, if the protein source contains very little lysine, a CP content of 20% would be deficient, since we would have to increase CP in order to meet the lysine requirement. Because corn contains very little lysine, swine cannot subsist solely on a corn diet. Put another way, they cannot consume enough corn in a day to meet their daily lysine requirement. Therefore, swine producers typically incorporate soybean meal, (which contains about 48% protein and a considerable amount of lysine) into swine diets to help meet their lysine needs. Other essential amino acids including methionine, threonine, and tryptophan can present similar problems in swine as well as other species. Providing several protein sources in a single diet is a common way of balancing amino acid content. In another more extreme example, a 40% CP diet that contained little or no arginine would be fatal to cats within an hour or two of eating the meal. This is because arginine is required for the synthesis of several key metabolic compounds and an imbalance caused by the lack of arginine results in a rapid and fatal disruption of these metabolic functions. Most protein sources contain ample amounts of arginine so this is rarely a problem, but it points out the importance of formulating diets based on amino acid content (protein quality) rather than on a crude protein basis.

Nitrogen balance
Nutritionists often refer to "nitrogen balance" when speaking of protein needs. They use nitrogen as an indicator because it is easily assayed using a "Kjeldahl" analysis, and the primary nitrogen source for animals is dietary protein. Nitrogen balance can be easily summed up as the amount of nitrogen (protein) coming in compared to the amount of nitrogen leaving the animal. Nitrogen can leave the animal in forms including urea and ammonia in the urine, as undigested protein in the feces, and as protein incorporated into bacterial cells. The latter can be substantial, as up to 80% of the fecal mass can consist of bacteria. Urea nitrogen is an indicator of "metabolized" protein. That is protein that has been absorbed by the animal as amino acids and was used for some metabolic function. For metabolic use, amino acids are often "deaminated" (the nitrogen removed) and the nitrogen is then excreted in urine. On the other hand, much of the nitrogen excreted in the feces has not been absorbed by the gut, thus it has not been metabolized.

Although amino acids are generally thought of as being used to make protein, they can also serve as an energy source. One of the reasons the protein requirement of cats is so high is that they have evolved methods of extracting energy from pure meat diets which are primarily protein. Herbivores and omnivores on the other hand depend more on plant carbohydrates for their energy rather than amino acids. In the process of using amino acids for energy, nitrogen is removed and, if not excreted, it would result in a systemic increase in ammonia. Nitrogen in the form of ammonia is very toxic and animals go through great lengths to ensure that it is promptly excreted or incorporated into less toxic compounds such as urea or uric acid.

We have strayed somewhat from our discussion of nitrogen balance so let's return to that topic. If excreted nitrogen is greater than intake of nitrogen the animal is said to be in a negative nitrogen balance. This indicates a deficiency and that protein and amino acids are being used faster than they are being taken in. Again, this use may be for assimilated protein, for energy, or for other metabolic needs. A negative nitrogen balance can arise for several reasons, but one of the most common is inadequate energy intake. If intake of energy does not meet maintenance needs, the animal is forced to live off its own tissues. Once reserve fat and other energy stores are used up, the animal will start using amino acids from its own muscle protein for energy. As these amino acids are used, nitrogen is released and excreted, thus resulting in a "negative" nitrogen balance.

Another reason that a negative nitrogen balance may occur is an imbalance in amino acid ratios (poor protein quality). If amino acid "A" is in short supply, amino acid "B" may have to be converted into amino acid "A". This requires energy, and in some cases that energy comes from other amino acids with the release of nitrogen as a result. In some cases it takes two or more amino acids to make one. When this occurs the extra nitrogen group(s) must be excreted or used elsewhere. If excreted, these nitrogen units may contribute to a negative nitrogen balance. This is very simplified overview of protein digestion and metabolism and obviously there is much more to this story than we will be able to address in this class. Hopefully this discussion will give you a basis to pursue other related topics should you need to do so.

 Special note on protein and ruminants

In ruminants, microbes have first access to proteins. As a result, much food-derived protein is degraded in the rumen and restructured into bacterial protein, before passing into the abomasum and SI. Nonprotein nitrogen (NPN) can also be used by cattle and other foregut fermentors for protein production. NPN sources include compounds such as ammonia (NH₃) and urea. Thus these substances can be added to forage diets to enhance protein production from those feeds. Like dietary protein fed to a ruminant, the NPN is incorporated into microbial protein which can then be utilized by animal. In fact, rumen microbes, and thus the cattle housing them, can subsist without the consumption of real protein or even peptides, assuming NPN, energy, and carbohydrates are provided in sufficient quantities for the formation of amino acids. Another advantage of the ruminant system is that essential amino acids, often a concern in monogastric nutrition, are generally of little consequence to the ruminant. Because microorganisms have the mechanisms to construct all amino acids (including essential ones that mammals cannot produce), from NPN and carbohydrates, the ruminant does not require the inclusion of essential amino acids in the diet, at least under normal conditions. Under conditions that place high demands on the animal, such as lactation (very relevant to dairy herds), wool growth, or environmental stress, a positive response to amino acid supplementation may occur. Supplementation with feed sources that provide escape protein (protein that escapes microbial degradation and thus becomes available "as is" for digestion in the abomasum and SI) is one way of providing specific amino acids to the ruminant. Corn, for example, contains a good deal of escape protein, thus if fed in proper quantities, that grain can have a positive impact on the protein production in rapidly growing cattle. Once microbial protein and escape protein pass into the abomassum and SI, digestion and absorption of protein in ruminants is similar to that of nonruminants.

Energy

As with protein, energy needs vary considerably between species as well as between various phases of the animal's life, including pregnancy and lactation. We have already touched on energy sources in our earlier discussion of fore- and hind-gut fermenters. As mentioned in that discussion, carbohydrates including starch, fats, fiber (mostly cellulose and hemicellulose of varying degrees of digestibility) can all provide energy in a diet, assuming the animal is capable of converting those sources into a usable substrate. Additionally, as we noted in our discussion of protein, amino acids can also serve as an energy source.

Energy is needed for many functions, including movement and work, to drive metabolic and catabolic processes for maintenance and growth, and for maintaining body heat in homeotherms. Dietary energy is usually measured as kilocalories of heat. Energy content of a diet can be determined by a method known as "bomb calorimetry" which involves burning the components and measuring the amount of heat produced. However, other methods must be used to determine available energy for a particular species. While grass or other forage may contain a considerable amount of energy for an Elk, this means nothing to a dog or cat that is not able to extract that energy. To determine the amount of usable energy, different fractions of energy compounds must be extracted and analyzed separately and interpretation must be based on the animal to be fed. Energy-bearing fractions of a diet are determined using a number of extraction methods followed by determination of respective energy content. Additionally, the digestive capabilities of the animal must be understood so there is a clear picture of which energy substrates can actually be used by a particular species.

Most animals can utilize dietary fat and simple sugars (mono and di-saccharides) as energy sources. However, not all animals are designed to derive all or even most of their needs from these sources. In fact, feeding diets high in starch and sugars can have serious consequences in ruminants and other fermenters. These substrates act as highly fermentable substrates for rumen bacteria, which may then produce excessive amounts of VFA, lowering rumen pH and possibly resulting in fatal acidosis. Diets too high in energy can also produce laminitis in horses, and high concentrations of sugars such as glucose and sucrose can lead to profuse diarrhea in monogastric animals from malabsorption. Malabsorption occurs because of osmotic effects of the dissolved sugars drawing water out of the intestinal tissues and into the gut lumen. On the other hand, high fiber diets can cause serious diarrhea in strict carnivores for reasons that are not yet clearly understood. Thus, as in our discussion of protein, it can be seen that a balance of energy sources is required and the particular balance depends on the species for which the diet is formulated.

A special word concerning fats
As with amino acids, some fat compounds are essential to animals. These essential fatty acids (EFAs) are necessary for proper cell structure, synthesis of certain metabolites, and production of prostaglandins. Linoleic acid (18 carbon) is one of the most commonly discussed EFAs. If linoleic acid is provided in sufficient amounts, herbivores and omnivores can produce other necessary fatty acids, including arachidonic acid (20 carbon), which also plays many important roles in metabolism. Once again, however, strict carnivores, such as cats, mink, and some marine mammals present a problem in that they lack the capability to produce arachidonic acid. Thus this fatty acid is essential to those species and must be included in the diet. Linoleic acid is common in most plant-based energy sources with the exception of coconut and palm oil. Conversely arachidonic acid is absent in plants, being found only in meat, milk, and seafoods. Consequently, if cats are fed only dog food, which is often cereal-based, they may develop an EFA deficiency stemming from the lack of arachidonic acid. EFA deficiencies will also develop in marine animals if their fish-based diet is stored improperly or for too long. As mentioned before, this is due to degradation of essential fatty acids in the diet. Some consequences of EFA deficiencies include an irregular or non-existent estrous cycle (from decreased hormone production), skin abnormalities and lesions, slow healing, and various other maladies mostly associated with cell integrity.

Minerals

Minerals are required in varying amounts for proper nutrition. Severe deficiencies can cause dibilitating diseases and death. Grazing animals generally take in sufficient amounts of minerals from pasture forages, hay or silage. For other livestock diets, minerals are generally provided via premixes which when incorporated into the diet at the recommended level (often 1 to 2% of the diet) will provide proper concentrations of the various minerals.

Macro elements
Dietary minerals can be divided into two broad groups; macroelements and micro- or trace elements. Macro elements include calcium, phosphorus, magnesium, zinc, sodium, potassium, chloride, and sulfur. Of this group, nutritionists are generally most concerned with calcium and phosphorus.

Calcium and Phosphorus
These two elements are needed in large quantities for proper bone formation and for various other needs. Calcium is one of the most commonly expressed mineral deficiencies in captive wild animals. As one might guess, production of milk, eggs, and even antlers requires increased intake of both Ca and P, so the requirement for these macro elements can change tremendously within a single season.

The real concern with calcium and phosphorus is that these two elements share a somewhat antagonistic relationship. Excess phosphorus, for example will form insoluble complexes with calcium, thus increasing the dietary need for calcium. Proper dietary calcium:phosphorus ratios range from about 1.3 : 1 to about 2.3 : 1, depending on the species and phase of growth. A particular disorder associated with improper Ca to P ratio is Nutritional Secondary Hyperparathyroidism (NSH). Calcium concentrations in the blood are controlled by calcitonin and parathyroid hormone. Hyperparathyroidism can result when insufficient Ca or excess P in the diet lead to a continued call for Ca in the blood, thus leading to hyperactivity and ultimately hyperplasia of the parathyroid gland. At this point, regulation of Ca is lost and decalcification or osteoporosis of bone occurs, leading to debilitating disorders.

Some seeds and cereal grains are deficient in Ca and thus birds and small mammals that might be fed only seeds and nuts have been known to develop NSH. Additionally, carnivores that are fed strictly meat with little or no bone material, will develop similar maladies. Wild rodents and other mammals that feed primarily on seeds and similar food sources instinctively seek out bones, teeth, and antlers lying on the ground as a convenient source of Ca and P. For captive animals, bone meal is a cheap and convenient additive to ensure sufficient intake of these two minerals.

Phosphorus is usually found in high concentrations in plant material, however, much of it is usually tied up in a compound known as phytic acid. Animals generally cannot degrade phytic acid, thus the phosphorus bound in this form is not available for absorption. It is therefore important that any analysis of P in a food source take into account what is bound (unavailable) and what is free (available). Phosphorus is most often supplied in commercial diets from inorganic sources such as dicalcium phosphate. Such supplementation ensures that this element is in proper supply to the animal. Phytase is a bacterial enzyme that can degrade phytic acid in the plant material, freeing additional phosphorus for absorption by the animal. Phytase is coming under increasing use in livestock diets to decrease the amount of inorganic phosphorus that needs to be added to the diet. This strategy also decreases the amount of phosphorus excreted in animal waste, thus reducing the impact on the environment. Because inorganic sources of phosphorus are cheap, the primary reason for the interest in phytase is its effect on nitrogen wastes from livestock operations rather than decreasing feed costs.

Sodium

Sodium (Na) is needed to maintain electrolyte balance and to act in transport systems, pH balance, and for proper function of the nervous system. As such, it is required in considerable amounts in all animals. While meat contains plenty of sodium, plant and cereal-based foods are generally deficient in Na. As a result, herbivores can sometimes develop Na deficiencies in a captive environment. With a few exceptions of very specialized species, the sodium requirement is similar for most animals. Generally, Na should be fed at about .2 to .5% of the diet, assuming normal feed and water intake. Salt can also be provided by free access to a salt block. Sodium is easily excreted from the body if adequate water is available, thus there is generally little concern that the animal will consume too much salt if reasonable levels are included in the diet or provided a salt lick.

Potassium

Although potassium plays many important metabolic roles, a deficiency of this element seldom occurs due to its relatively high levels in plant and animal tissues. Thus we will not discuss this element in any more detail here.

Magnesium

Magnesium is also an important constituent of bones and it also serves an important role in many enzyme systems, including DNA transcription and translation. Like potassium it is generally found in sufficient amounts in most food sources. However, dairymen and cattle producers sometimes see a magnesium deficiency when animals graze on fast-growing lush pastures in the spring. Symptoms include nervousness, loss of appetite, loss of equilibrium, tetany, and convulsions. This disorder is known as grass tetany (or grass staggers) and although it is known that a deficiency in magnesium plays a role, the exact cause is not clear. Deer have also exhibited the same disorder under similar circumstances. While sufficient magnesium appears to exist in the pasture grasses, other factors, possibly excess nitrogen or organic acids may decrease absorption or availability of the magnesium, leading to the disorder.

Trace elements
Trace or micro minerals include elements such as iron, iodine, zinc, copper, selenium, and manganese. As the name implies, they are required in lesser amounts than are macro elements. Iron, iodine, copper, and selenium deficiencies are the most common disorders noted in captive or domestic species.

Iron

Iron deficiencies can be common in captive animals that do not have access to soil. The most common deficiency associated with iron is anemia. Bottle-fed animals can be particularly prone to iron deficiencies, especially when the formula consists mostly cow's milk. The milk of ungulates has lower levels of iron than does the milk of most other mammals. In addition, chelating agents in cow's milk tie up many trace metals, including iron. Thus iron may need to be supplemented by direct addition to the formula, through injection, or by allowing the animal access to soil or fresh vegetation.

Iodine

Iodine deficiencies are expressed mostly as thyroid disorders. Many foodstuffs including seeds, meat, and freshwater fish are deficient in iodine, thus enlargement of the thyroid is common in captive animals where little attention is given to their nutrition. Iodine can also be derived from the soil but its content can vary considerably across geographic regions. As a result, iodine concentration in plants and other foodstuffs may also vary, depending upon their region of origin.

Copper

Copper is another trace mineral in which deficiencies can occur, particularly in carnivores. Copper concentrations vary considerably in meat products. Meat derived from muscle tissue is low in copper whereas liver, kidney, and brain contain much higher concentrations. Thus feeding strict carnivores a meat diet that is devoid of animal organs or entrails can lead to copper deficiencies. Symptoms range from decreased hair and plumage color to lethargy, anemia, and osteoporosis.

Selenium

It has only been in more recent years that selenium deficiencies were recognized. Selenium works in concert with vitamin E to prevent free radicals that can lead to oxidation of lipids and destruction of cells. White muscle disease is caused by lack of selenium. It results from the destruction of cell membranes that lead to "leakage" of cell contents and lack of cellular homeostasis. This disease can affect many animals including birds, small mammals, and deer. Like iron and iodine, selenium also exists in the soil and its concentration can vary tremendously within a small geographic region. To add to the problem, small excesses of selenium can be toxic. In fact, toxicity can result from eating plants that were grown in areas where high selenium concentrations occur in the soil. As a result of this toxicity, selenium is one of the few elements where inclusion in livestock and pet diets is under strict FDA control. Thus it is illegal for producers, pet owners, or anyone else to supplement commercial or privately manufactured diets with selenium without FDA approval.

Vitamins

Vitamins are compounds that are required as co-factors or co-enzymes in metabolic reactions. They are not used directly as energy components or structural components. Many are readily available from plant sources, while others can be produced within the animal. Considerable amounts of some vitamins are also produced by the gut microflora and can be used by the animal. Vitamins are categorized by their solubility in either water or fat. This has relevance to how and where they can be absorbed by the gut. Vitamin concentrations in a diet are generally discussed in terms of activity (IU) since, for most vitamins, several forms of differing activity can occur. As with minerals, vitamins are often incorporated into commercial feeds by way of premixes which are intended to be used at specific concentrations in order to provide the appropriate amounts of individual vitamins.

I will try to keep the description of the various vitamins as brief as possible. Tables taken from C. T. Robbins (1993) will be provided in class that give more detailed information on function and deficiencies of fat and water-soluble vitamins.

Fat Soluble Vitamins

Vitamin A

Vitamin A appears in several chemical forms including retinol and retinal. Retinoic acid, yet another similar form, can fulfill most but not all of the requirements attributed to this vitamin. Vitamin A is important in visual processes and cell maintenance and differentiation. While vit A is not found in plant stuffs, a precursor (ß-carotene) is available in plants, especially leafy green vegetation. Most herbivores and omnivores can produce sufficient vit. A through ingestion of ß-carotene from plant stuffs. Strict carnivores, however, generally lack the ability to convert ß-carotene to vitamin A.

A major storage organ for vit A is the liver, with much lesser amounts being found in other organs and muscle. Therefore it is important that strict carnivores are allowed to consume some internal organs, especially liver (see caution in rest of this paragraph) or some supplementation, possibly from a commercial source, should be included in the diet. Caution: vit A can be toxic in excess, although the precursor, ß-carotene, is generally not a problem in excess. The symptoms of excess vit A are varied and include bone brittleness, hemorrhaging, and reproductive problems. Thus care should be taken not to exceed the recommendation for any particular species. Additionally, carnivores, including many aquatic mammals at the top of the food chain, contain very high concentrations of vit A in their livers. As a result, animals (and humans) can receive toxic levels of vit A if they consume the liver of some carnivores.

Vitamin D

Vitamin D comes in two major forms D₂ (ergicalciferol) and D₃ (cholecalciferol). Vit D is very important for calcium uptake and regulation. Rickets in both animals and humans is the common expression of vit. D deficiencies. Metabolically, mammals are more dependent of vit D₃ but can utilize D₂, although much less efficiently. Fish, amphibians, reptiles, and birds cannot use the D₂ form at all and thus require the D₃ form. You may already be aware that sunlight plays an important role with regard to vit. D needs. Ultra violet light contacting the skin converts 7-dehydrocholesterol, a sterol produced naturally by animals, to a vit D₃ precursor. It is interesting (at least to me) that vit D₂ production does not require sunlight and thus its limited use by mammals may have evolved because of the nocturnal habits of many early mammals.

Vit D is not stored in great quantities in animal tissue, thus a constant supply from the diet and/or UV irradiation is required. Confinement-reared animals without access to sunlight and consuming inadequate diets can express a vit. D deficiency within a few days. Be aware that UV radiation does not penetrate most glass and plastics thus simply placing a terrarium next to a window will not help your favorite herptile as far a vit. D is concerned. It is important that bulbs with proper UV spectrum and/or diets that contain sufficient vit. D be supplied. Milk of many mammals is also deficient in vit. D and thus bottle-fed infants without access to sunlight are prime candidates for vit. D deficiencies. Fish and fish products generally contain sufficient levels of vit. D₃, although as with other nutrients, improper or lengthy storage can greatly diminish these levels. Commercial forms of vit. D are available but as with vit. A, large excesses can lead to toxicities. Bone abnormalities can result with excess as well as a deficiency of this important vitamin.

Vitamin E

Vitamin E plays a significant role in the reduction of free radicals which can damage cell membranes and other lipid-containing structures. Vit. E and selenium compliment each other in the role of free radical reduction; however, one should not attempt to alleviate a vit. E deficiency by increasing selenium or vice versa. Several forms of this vitamin exist as compounds known as tocopherols. Vit. E is only synthesized in plant and bacterial cells thus herbivores derive vit E from plants and carnivores derive vit E from meat and other animal products. Levels of vit. E are generally high in fish products, however these levels quickly decrease during storage, especially if the fish contains excessive fats and oils. It has been found that vit E. deficiencies can occur readily in fish-eating birds in captivity if the diet is restricted to dead, partially rancid fish. It should also be noted that vit. E deficiencies are very common in captive rhinos and elephants. This is probably because they are adapted to plants with higher levels of vit E than are found in domestic hay. Additionally, other compounds having vit. E activity may be specific to Asian plants that can be utilized by these large mammals. Commercial forms of this vitamin are available for supplementation. Again, excesses should be avoided as they may adversely affect other metabolic processes.

Vitamin K

Vitamin K is the last fat soluble vitamin to discuss. It is most noted for its role in blood clotting. Two natural forms exist; phylloquinone (K₁), which is synthesized by green plants and menaquinone (K₂), synthesized by gut bacteria. Menadione is a commercial form of the vitamin. Because of its widespread occurrence in plant stuffs and production within the animal, vit. K generally only needs to be included in purified or pure meat diets. Vitamin K is generally not toxic except when included at very high concentrations, thus the vitamin can be routinely supplemented in most diets without much concern.

Water soluble vitamins

Deficiencies of these vitamins are generally not a problem due to their synthesis by gut bacteria and common occurrence in most feedstuffs. As such, there is much less information available regarding these vitamins. Because of animals' reliance on intestinal microflora for many of these vitamins, diets for patients treated with broad spectrum antibiotics or other therapies that impact on enteric populations should be supplemented to compensate for potential loss of synthesis.

Vitamin C

Vitamin C (ascorbic acid) can be synthesized by many animals including amphibians, reptiles, some birds, and some mammals. Because the ability to synthesize this vitamin is variable among species, and excess can be given with little concern for toxicity, this vitamin should be routinely supplemented for all captive animals via green plants, fruits, or commercial sources. Liver is a good source of the vitamin for carnivores.

Vitamin B1

Vitamin B1 (thiamine) is another water soluble vitamin for which at least some information is available. Unlike most water soluble vitamins, thiamine deficiencies are somewhat common in captive animals, especially aquatic mammals and birds. Although thiamine is found in fish, other compounds, especially thiaminase, in fish and shellfish degrade this vitamin during even brief storage. Thiaminase usually occurs in an inactive form in living animals and becomes active following death. However, active thiaminase can be found in some plants (including ferns and other lower vascular plants), baby chicks, which are often used as food for carnivores, and the heart and spleen of mammals. Thiaminase can also be synthesized by rumen bacteria, especially when grazers are fed high concentrate (high grain) diets. Ingested thiaminase can create a thiamine deficiency even when the vitamin is supplemented, so it is important that animal care experts be aware of this potential problem. If there is a question, determination of thiaminase activity in highly specialized or strict diets may be warranted.

Other water soluble vitamins

I don't want to burden you with reams of information on all these nutrients. I've pointed out some of the more important issues regarding selected nutrients and, as indicated above, I will be providing a table with additional information on these and other vitamins for your own use. Additionally, because much of the work involving these requirements for common livestock has been addressed through commercial vitamin/mineral premixes, we can quickly move on to more pressing issues.