Vitamins and Minerals

Vitamins and minerals are classified as micronutrients due to their small quantities required in a dog's diet in comparison to macronutrients such as fat, carbohydrate, and protein. These micronutrients play crucial roles in supporting the body's metabolic processes and must be provided in the diet to meet those needs. However, dogs have the ability to synthesize some vitamins themselves.

A well-balanced and formulated diet should provide sufficient levels of essential vitamins and minerals by incorporating a variety of ingredients that serve as sources for these micronutrients. Nevertheless, there may be instances where the appropriate supply or bioavailability of certain vitamins and minerals presents challenges. This can result in deficiency or potentially toxic excess, and diet formulation should account for these factors.

It is important to note that deficiencies in many vitamins and minerals tend to have cumulative effects and can take time for the signs of deficiency to manifest. This is particularly relevant for home-prepared diets where appropriate micronutrient levels may be poorly managed. Therefore, care should be taken to ensure that appropriate levels are provided. Additionally, there is a risk of inadequate nutrient levels in any diet that has not been properly formulated, stored, or processed.

A typical response-curve for micronutrients in the diet. Each micronutrient has its own specific response curve, and some will have much wider ‘safe’ intake zones than others.

It is imperative to understand that excessive intake of vitamins and minerals can lead to significant harm. Micronutrients have a specific deficient-optimal-toxic response curve, and some have a broader safe intake range than others. For instance, vitamin E has a wider safe level of intake, while selenium has a smaller one. Being aware of the roles, significance, signs of excess, and deficiency of essential vitamins and minerals in our dogs' diets can help ensure a safe and appropriate dietary supply. This can be achieved through the food fed, ingredients incorporated, or supplements used. Commercial diets typically use vitamin and mineral premixes to fortify their diets, compensating for nutrients lost or damaged during processing or storage. Home-prepared diets may require a mixture of ingredients to provide key micronutrients, and supplements may be necessary in case of shortfall or bioavailability issues. Specific micronutrient supplements may also be used to support specific health conditions in dogs, even when the dietary supply seems adequate.

Vitamins

Prior to the comprehensive understanding of vitamin chemistry, it was widely recognized that certain ailments were linked to dietary deficiencies. One such affliction was scurvy, which posed a significant health concern for seafarers on extended voyages, lacking access to fresh produce. With the realization that scurvy was caused by a deficiency in vitamin C, the provision of fresh limes to sailors became a standard practice, effectively reversing the condition.

Vitamins are essential to support many body functions, including energy release from food and bone health.

Dogs have the unique ability to synthesize their own vitamin C, but there are instances where additional supplementation may prove advantageous. While each vitamin has a recommended minimum dietary level, certain factors such as breed genetics, health conditions, and physiological state may require altered or managed levels of vitamin intake. The term 'vitamin' was coined by the Polish biochemist Casimir Funk before vitamin chemistry was fully understood. Originally, vitamins were named after letters of the alphabet, with nine vitamins from A to I described. Although some of this naming system remains, there have been revisions, with some compounds later discovered not to be true vitamins, such as vitamin F (now known to be essential fatty acids), and others being mixtures of several different vitamins - the vitamin B complex. Vitamins are organic substances that are essential for normal body function but are not utilized as energy sources or for body structures. They are classified as either water-soluble, which includes the vitamin B complex and vitamin C, or fat-soluble, which includes vitamins A, D, E, and K.

Water-Soluble Vitamins

The group of water-soluble vitamins encompasses vitamin C and vitamin B complex, which are identified by their specific names or numerical designations. These vitamins boast a broad safety margin, as any surplus is typically eliminated from the body, thereby minimizing the risk of toxicity or hypervitaminosis. Nevertheless, since the body does not store these vitamins, a consistent dietary intake is necessary. In canines, the majority of cases indicate that they are able to produce sufficient levels of vitamin C on their own, and their diet is sufficient in providing the necessary B vitamins.

Vitamin C

Canine physiology allows for the endogenous synthesis of vitamin C, rendering a dietary source unnecessary. Nevertheless, vitamin C is a potent antioxidant and may prove beneficial for highly active or convalescing dogs. Supplementation may also be advantageous for canines with hepatic dysfunction, as the liver is responsible for synthesizing this nutrient. Additionally, vitamin C plays a crucial role in promoting skin health, making dietary vitamin C a potentially valuable addition to certain canine diets.

B Vitamins

There are eight B vitamins and choline, a vitamin-like substance that was originally designated as vitamin B4 (see Table). The B vitamins play a crucial role in metabolic reactions and the release of energy from food. These vitamins are often found in the same foods, such as meat, eggs, nutritional yeast, and dairy, although some plants also contain them. Well-formulated dog foods typically provide sufficient levels of B vitamins, but supplementation may be necessary in certain circumstances. Genetic conditions and digestive illnesses can affect the absorption of B vitamins in the small intestine, and disruptions to the intestinal microbiome can also impact their synthesis. In such cases, supplementation with vitamin B12 may be useful. For active dogs, B vitamins are essential to support their metabolism and energy generation, and folic acid is critical for normal fetal development. Pregnant bitches may benefit from supplementation with folic acid before mating and during early pregnancy to reduce the incidence of developmental disorders. Dogs with skin and nail problems may also benefit from supplementation with biotin and other B vitamins. It is important to note that the bioavailability of B vitamins can be affected by other dietary ingredients. For example, biotin deficiency can result from feeding high levels of raw egg white, which contains a substance that binds to biotin, making it unavailable. Similarly, thiamine (vitamin B1) deficiency can occur when high levels of raw, white fish are fed due to an enzyme, thiaminase, that destroys the thiamine. Cooking can destroy thiaminase and minimize this risk.

The water-soluble vitamins of importance in the dog’s diet

The Fat-Soluble Vitamins

The fat-soluble vitamins, namely A, D, E, and K, are assimilated in the small intestine and predominantly accumulated in the liver and adipose tissues of the body. While these reserves can prove beneficial during instances of nutritional inadequacy, excessive levels of these vitamins can result in toxic outcomes. Certain fat-soluble vitamins are present in plant tissues as provitamins, which are transformed into functional vitamins post-consumption. Beta-carotene, or pro-vitamin A, frequently found in carrots, serves as a notable example in this regard.

Vitamin A

Canine physiology allows for a high threshold of excess dietary vitamin A, thereby minimizing the likelihood of toxicity. Vitamin A plays a crucial role in maintaining normal vision, immune and reproductive function, and overall skin and skeletal health. Inadequate levels of vitamin A can result in negative impacts on these systems, particularly during growth and development. Fortunately, vitamin A deficiency is a rare occurrence in dogs, as they are able to convert beta-carotene into the active form of vitamin A and commercial diets provide sufficient quantities.

Vitamin D

Dogs have a restricted ability to produce the active form of vitamin D in their skin from sunlight, unlike humans. As a result, dogs require a dietary source of vitamin D to promote their skeletal structure and maintain normal levels of calcium and phosphorous in the body. The regulation of calcium and phosphorus levels in the body is closely linked to vitamin D. Insufficient or excessive amounts of these nutrients can lead to significant skeletal abnormalities, particularly in developing puppies.

Vitamin E

Vitamin E is a potent antioxidant that can be beneficial for highly active dogs and should be included in diets that are rich in polyunsaturated fatty acids, particularly when fish oils are added. Additionally, older dogs may benefit from vitamin E supplementation to mitigate the effects of age-related changes. Commercial dog food often includes vitamin E as an antioxidant to prevent rancidity. It's important to note that vitamin E works synergistically with selenium, and maintaining balanced levels of both nutrients is crucial for optimal function.

Vitamin K

Vitamin K is a crucial group of compounds that play a vital role in the normal clotting of blood. While deficiency is rare, dogs that have ingested certain forms of rodent poison are treated with vitamin K. The intestinal microbiome of dogs synthesizes vitamin K as a by-product, which can be absorbed and utilized. However, commercial diets also provide sufficient levels of this essential nutrient.

Minerals

Minerals play a crucial role in maintaining normal body structure and function in dogs. It is important to note that while they are required in small amounts, they are essential. Minerals are identifiable by their common name and characteristic chemical symbol. While some minerals such as iron (Fe) and copper (Cu) are well-known, others like manganese (Mn) and selenium (Se) are equally important for metabolic function. Macrominerals, such as calcium and phosphorus, are required in larger quantities (g/day) than microminerals (mg/day), also known as trace elements. The latter, including cobalt (Co) and molybdenum (Mo), are more numerous. It is worth noting that all minerals are inorganic, single chemical elements that do not include carbon. However, minerals are often found in specific chemical forms within foods, often as salts, meaning the mineral element forms a compound with another element. Therefore, the mineral forms that exist in different foods can affect their bioavailability and must be considered when formulating diets.

Minerals are involved in a number of key body processes, including skeletal structure, fluid balance, energy generation and functioning of the nervous system.

Minerals constitute around 4% of an animal's body weight, with the majority being present in the skeleton, which is abundant in calcium (Ca) and phosphorous (P). Although other minerals are equally crucial, their presence is relatively minimal. Iodine (I), for instance, plays a pivotal role in regulating metabolism and the proper functioning of the thyroid gland.

The fat-soluble vitamins of importance in the dog’s diet

Electrolytes

Electrolytes are a crucial classification of minerals that facilitate the conduction of electrical impulses in the body, playing a vital role in maintaining normal cell function. These minerals are essential for various physiological processes, including the regulation of water balance and pH levels, as well as the transmission of nerve impulses. Notable examples of electrolytes include calcium (Ca), potassium (K), sodium (Na), phosphorus (P), and chloride ions. While electrolytes are lost during perspiration, dogs typically experience minimal electrolyte loss through this route due to their limited sweating capacity. In most cases, a well-balanced diet should provide adequate levels of electrolytes for dogs.

Mineral Requirements

Determining the exact dietary requirements for minerals can be a challenging task. Reference ranges are available to indicate minimum to maximum levels; however, due to the wide variation in the biology of domestic dogs, a single ‘recommended daily amount’ to cover all individual dogs and their situations may not be appropriate. Furthermore, mineral interactions with each other and other nutrients can cause additional issues if not carefully balanced. Some minerals have antagonistic interactions with others, while others work together, and levels need to be carefully considered. For example, there is a close relationship between selenium and vitamin E, and their levels require careful consideration. It is also important to note that some minerals have a narrow safety margin, and toxicity is a concern when supplementing. Although there are more than sixty minerals found in the dog’s body, not all of them are considered essential. Therefore, it is crucial to consider minerals individually and prioritize those that are important for our dogs.

Macrominerals of Importance in the Dog’s Diet

Calcium (Ca) and Phosphorous (P)

Calcium (Ca) and phosphorus (P) play a critical role in skeletal development and overall health. While they have other functions in the body, their bioavailability can vary and their requirements change throughout a dog's life. To ensure balanced nutrition, a Ca:P dietary ratio of 1.2:1 is generally considered ideal, with a minimum of 1% Ca and 0.8% P for growth and reproduction. Large-breed puppies are particularly sensitive to Ca and P levels, and careful formulation is recommended to ensure balanced levels. For adult maintenance, minimums of 0.6% Ca and 0.5% P are suggested. It is important to note that Ca and P from plant sources are less bioavailable than from animal sources. Fresh meat, meat meals, and organ tissue tend to be low in Ca, while P is widely distributed in foods. Poorly formulated diets that are rich in meat can cause unbalanced levels of Ca and P, leading to skeletal disorders, especially in growing puppies. Excess Ca can also be problematic, resulting in bone growth and development issues. Avoiding excess Ca supplementation is important if an otherwise balanced diet is fed. If you are home-preparing a diet, ensuring that the levels of Ca and P are appropriate is essential. For dogs with renal (kidney) problems, levels of phosphorus (as phosphate) in the diet might need to be reduced as part of dietary management.

Potassium (K)

Potassium (K) is a crucial electrolyte necessary for maintaining normal nervous system function. It works in conjunction with sodium (Na) to regulate the body's fluid balance. Insufficient levels of potassium can have adverse effects on heart function and may lead to weakness, growth issues, and diarrhea.

Sodium (Na)

Canine physiology appears to tolerate high levels of dietary sodium more effectively than human physiology. While hypertension and high blood pressure resulting from high-sodium diets are rare in dogs, increased water intake is a common occurrence that can be beneficial in certain circumstances. Sodium is a crucial electrolyte, and a steady supply is necessary due to ongoing excretory losses. Dehydration is a significant concern for active dogs, and sodium deficiency can exacerbate this issue.

Sulphur (S)

This mineral serves a crucial structural role as a fundamental constituent of amino acids and proteins within the body, specifically in tissues such as skin and hair.

Magnesium (Mg)

Magnesium (Mg) plays a crucial role as an electrolyte and in the formation of skeletal structure. It also contributes significantly to the generation of energy in cells, making it particularly important for highly active dogs. Mg is commonly found in the form of mineral salts in bones and certain plant-based sources, particularly cereals and grains. Although uncommon, a deficiency in Mg can lead to weakness and uncoordinated movement. Conversely, an excessive intake of Mg can result in a laxative effect.

Common macrominerals of importance in the dog’s diet

Chlorine (Cl)

Chloride (Cl) is typically found as chloride ions and plays a crucial role as an electrolyte in regulating the body's pH levels. Additionally, it is a vital component of hydrochloric acid (HCl) in the stomach, which is necessary for proper digestion.

Microminerals of Importance in the Dog’s Diet

Iron (Fe)

The proper transportation of oxygen in red blood cells and muscle is contingent upon the presence of Fe, a crucial component of the pigments haemoglobin (in blood) and myoglobin (in muscle). The absence of Fe can result in anaemia, fatigue, and, in some cases, pica - the consumption of non-food items such as soil. Although absorption is well regulated, Fe toxicity is infrequent. Nevertheless, excessive levels can lead to constipation.

Copper (Cu)

Copper is a crucial mineral that plays various essential roles in the body. Its deficiency can negatively impact the pigmentation, hair, skin, and nails. Copper is also involved in the formation and functioning of red blood cells and acts as an enzyme co-factor for metabolic reactions. However, excessive copper levels can be toxic, leading to liver disease since the liver is the primary storage site for copper in the body. Certain dog breeds, such as Bedlington terriers, Labrador retrievers, Doberman pinschers, West Highland white terriers, and American cocker spaniels, are more susceptible to potential copper toxicity. Therefore, it is advisable to monitor and manage copper levels in their diet while seeking veterinary support and guidance. Although there has been a recent trend of liver disease associated with copper toxicity in dogs, not all dogs are at risk. If concerned, it is recommended to seek further advice from the manufacturer regarding the diet's complete nutritional analysis.

Bedlington terriers can suffer from an inherited condition where there is excess storage of copper in the liver which can lead to toxic consequences.

Iodine (I)

The proper functioning of the thyroid gland and hormone production is reliant upon iodine. A deficiency of this essential nutrient can lead to significant issues with hormonal functioning, growth, and overall metabolism. Prolonged deficiency may result in goitre, which is characterized by an enlargement of the thyroid gland in the neck. Fish and seaweed are excellent dietary sources of iodine.

Cobalt (Co)

Cobalt is a crucial component of vitamin B12 and plays a significant role in supporting optimal bodily function and preventing the onset of anaemia.

Zinc (Zn)

Zinc is a crucial mineral that plays an essential role in supporting overall health and wellbeing. It is involved in various functions, including reproduction, skin health, and immune system function. Since the body has limited storage capacity for zinc, it is imperative to obtain it through dietary sources. The majority of zinc absorption occurs in the small intestine, and any excess is excreted in the feces. Certain breeds, such as huskies, may have genetic predispositions that affect their ability to absorb and metabolize zinc, making them potential candidates for zinc supplementation.

Manganese (Mn)

Manganese (Mn) serves as a cofactor for enzymes involved in metabolic processes, similar to many other minerals. Additionally, it plays a crucial role in maintaining bone and cartilage health. Supplementation with Mn may prove beneficial for dogs experiencing joint issues.

Selenium (Se)

Vitamin E and selenium have a crucial role as antioxidants in the body, working together in synergy. It is imperative to maintain a balanced intake of these nutrients in the diet. Selenium is particularly important for active dogs and situations where there is a higher level of oxidative stress, such as in older dogs or those with inflammatory conditions. However, it is important to exercise caution when supplementing with selenium, as it is a highly toxic mineral.

Common microminerals (trace elements) of importance in the dog’s diet

Summary

• Micronutrients such as vitamins and minerals are crucial for supporting life and must be present in adequate amounts in the diet.
• Certain vitamins can be produced from dietary precursors or by intestinal microbes.
• Fat-soluble vitamins consist of vitamins A, D, E, and K.
• Water-soluble vitamins include the B complex and vitamin C, which dogs can synthesize.
• Although minerals are required in small amounts compared to other nutrients, they are vital for normal biological processes. For example, proper levels of calcium and phosphorus in the diet are necessary for skeletal health.