> Common Health Issues|
|Greyhound - Common Health Issues|
|Building better bones |
Fractures, splints, breaks, deformities are all bone related injuries that are very much dreaded within the greyhound industry.
Why? Because they mean time off from training and racing and are probably linked with a hefty vet bill or, worse still, could mean the end of a promising racing career.
Fractures, splints, breaks and deformities are injuries that could be related to a weakness of the skeletal system. The racing greyhound’s skeleton in particular endures significant loads, withstanding up to 2.5 times the dogs body weight on the inside front limb up the straight and up to 5 times during a sharp turn on a race track. The wrist joints of the front limbs experience pressures of up to 500psi when cornering during a race1, a considerable force when comparing this amount with the average car tyre, which contains 30 – 40psi.
Ensuring the skeletal system is healthy plays an important role in prevention of bone related injuries. In this editorial, we will run though the role of the skeleton, the nutrients required for healthy bones and also some of the bone related diseases that are directly related to nutrition.
|The function of bones |
Bone is one of the important tissues of the skeletal system. Bones act as the supporting framework for the body’s organs and other structures; they provide areas for muscles to attach and contain bone marrow for the production of both red and white blood cells. Bones also play an important role in mineral balance, storing a reserve of calcium and phosphorus within their matrix. These two minerals are stored in the bones at a ratio of approximately 2:1, along with a small amount of magnesium2.
Bone is continually being remodelled, a complex cycle which involves forming new bone and eroding and resorbing old bone in preparation for new bone remodelling. This process of bone remodelling takes several months to complete.
|Vitamins and minerals important for bone |
An adequate and correctly balanced supply of calcium and phosphorus is required for skeletal maturation, development and strength in young growing greyhounds and for bone remodelling in training and racing greyhounds. A typical greyhound diet traditionally contains meat, which is high in phosphorus but low in calcium.
Calcium is the mineral of greatest abundance in the greyhound body. The requirements for calcium are greatest during the formation of bones and teeth throughout the growth phase, which begins in the foetus prior to whelping. Calcium also plays a vital role in a wide variety of physiological and metabolic processes throughout life, including muscle contraction, blood coagulation, nerve impulses and intracellular chemistry3.
99% of calcium is found in the skeleton and teeth4. Research suggests the amount of calcium stored in the body doubles from approximately 6 mg/kg of bodyweight at birth to 12 mg/kg of bodyweight in adult dogs3.
Phosphorus is the second most abundant mineral in the greyhound body, with an estimated 86% of phosphorus found in the skeleton. Phosphorus also plays a structural role in DNA, RNA (for cell metabolism and turnover), locomotion and overall energy metabolism including acid-base balance3.
- Calcium and Phosphorus work together
Due to the wide-ranging functions of calcium and phosphorus throughout the body, a complex system exists for maintaining the correct balance of those minerals in the circulating blood, ensuring that adequate levels are available for immediate metabolic requirements.
Hormones are responsible for regulating the amount of calcium and phosphorus circulating in the bloodstream. The major hormones involved in this process include parathyroid hormone (PTH) and calcitriol.
Calcitriol is the most active form of vitamin D, produced in the body from the dietary Vitamin D source, typically in the form of cholecalciferol (vitamin D3)5. It must be noted that Vitamin D is an essential vitamin in dogs and cats (ie. it must be provided in the diet), as it cannot be synthesised in these species under the influence of sunlight - unlike in other mammals.5
- Other minerals are also involved
Zinc and magnesium are also important in the development and maintenance of healthy bone and a wide variety of other metabolic processes. Zinc has a vital role in production of bone, and thus is a critical dietary requirement throughout life3. Magnesium is involved in over 300 metabolic processes including calcium absorption, secretion and function of hormones and it plays an important role in the mineral function of bones and teeth3.
|Bone abnormalities associated with incorrect mineral supply|
- Calcium deficiency
If a greyhound’s diet becomes deficient in calcium, a condition known as Nutritional Secondary Hyperparathyroidism develops. The low calcium level in the diet reduces the circulating level of calcium in the blood. This stimulates Parathyroid Hormone (PTH) and Calcitriol to begin resorption of the calcium reservoirs stored in bone. Calcium is removed from the bones and enters the bloodstream enabling other essential bodily functions such as nerve and muscle activity and blood clotting to occur.
Specifically, Calcitriol stimulates increased calcium (and phosphorus) absorption from the gut, while PTH and Calcitriol act together to stimulate bone resorption to draw calcium and phosphate from bone.
This reduction of calcium in the bone mineral content leads to skeletal abnormalities and weaknesses such as bone deformities and fractures.
- Vitamin D deficiency
As we discussed last week greyhounds require a suitable source of vitamin D in their diet. Greyhounds receiving insufficient vitamin D in their diet are at risk of developing the disease known as “rickets”. The low intake of vitamin D limits the amount of Calcitriol that can be synthesised internally, which in turn, limits the amount of calcium absorbed from the gut. This disrupts the normal circulating calcium and phosphorus balance.
Dogs suffering from rickets initially develop clinical signs of lethargy and general loss of muscle tone which in turn does not allow them to run quickly3. Over time, the internal mechanisms for maintaining the correct circulating mineral balance induces bone resorption, in an attempt to return the blood calcium levels to normal.
As the condition progresses, swelling and bending of the bone occurs – the extent dependent on the degree of weight bearing. Profound muscle weakness and lameness are common in such dogs, due to disruption in normal functions of bone, muscle and nerve tissue caused by mineral deficiency or imbalances3.
- Phosphorus toxicity
Not surprisingly, dietary phosphorus levels also affect the balance of blood and bone minerals.
Increased levels of circulating blood phosphorus (eg. due to inadvertent excessive dietary intake) causes negative feedback on the production of Calcitriol, which in turn limits the amount of calcium and phosphorus absorbed from the gut.
Specific bone abnormalities, as well as muscle, nerve and metabolic disorders, can develop as a consequence of the amounts of vitamin D, calcium or phosphorus provided in the diet – whether they be too little or too much.
|Nutrition – energy levels and mineral balances are important|
Nutrition of young dogs is a subject frequently discussed between breeders and their veterinarians. Often, “traditional” thinking and scientifically based recommendations have to be brought together. However, it is important that clear guidelines and recommendations regarding nutrition are available for greyhound owners and breeders, because optimum nutrition is now recognised as the most important factor influencing growth rate and development6.
Daily weight gains and overall growth rates can vary greatly between dogs with different adult body weights. As discussed earlier, research findings over the last three decades indicate overfeeding, inadequate calcium and / or phosphorus supply (or incorrect calcium: phosphorus ratio), and other mineral or trace element imbalances (eg. Vitamin D deficiency) are important causes of skeletal developmental abnormalities.
Adequate feeding of growing and adult greyhounds most certainly requires a well balanced diet. It is expected that most reputable, commercially available “complete” dog foods would provide such a balanced diet, however, deficiencies or unbalanced diet composition can potentially occur with home-prepared diets not correctly supplemented with vitamins and minerals. The same risk exists for rations containing part commercial “complete diet” with an additional home-made meat and vegetable component, as it is difficult to determine the energy and mineral oversupply or shortfall of such a ration.
- Calcium absorption from the gut
Factors other than the specific calcium content in the diet can influence the amount of calcium that can actually be utilised by the greyhound (i.e. calcium availability).
Calcium availability is lower during growth periods and also decreases as the calcium content of the diet increases3. The calcium to phosphorus ratio in the foodstuffs may affect the absorption of calcium from the diet, as can the type of calcium supplement used. Furthermore, calcium appears to influence the availability of other dietary components such as zinc3.
Research has found that the bones of exercising dogs are 10% heavier relative to bodyweight as compared to sedentary dogs, and there is evidence that bone turnover is greater in exercising dogs. Fractures of the small foot bones are common in racing greyhounds and many areas of bone remodelling are evident using the specialised bone-imaging technique, called scintigraphy, often in the absence of radiographic signs of bone injury3.
It is also important to note that just as calcium deficiency can cause bone disorders, excessive calcium in the diet can also result in skeletal deformities and metabolic abnormalities, particularly in growing dogs. It is common practice for many dog owners to add calcium supplements, eggs, cheese, meats or other table scraps on an ad-hoc basis, to the commercially-prepared ration of puppies7. Such supplementation not only changes the absolute amounts of calcium and phosphorus in the diet but also alters the accepted 1.2 – 1.5:16 ratio of calcium to phosphorus.
The energy and mineral content of a greyhound’s diet should be based on consideration of such factors as the dog’s age, life-stage and levels of exercise and also with the view to achieving the correct dietary mineral balance.
- Pregnancy and lactation requirements
In addition to the high demands for calcium and phosphorus during growth are other periods of high-demand for those minerals.
During pregnancy the requirements of the bitch increase significantly in the mid to late period of gestation and during lactation and gradually decline to normal adult maintenance levels when lactation ceases. In late gestation the requirements for calcium increase, up to two and half times that of a resting greyhound and double again to five times the requirement of a resting greyhound during peak lactation.
When the weaning process begins, the provision of a well-balanced growth diet for the puppies is recommended, including adequate supplementation of vitamins and minerals, becomes essential for optimum growth and development.
The requirement for adequate dietary intake of minerals, particularly calcium and phosphorus, continues throughout a dog’s life, since mineral losses in the urine and faeces are a normal part of mammalian metabolic processes.
|Nourishing the bones|
The importance of providing an adequate dietary supply of calcium and phosphorus to all dogs cannot be overstressed. It is essential that dogs receive a balanced, scientifically formulated diet suitable to their life-stage and energy demands.
Authorities such as the National Research Council (NRC), Association of American Feed Control Officials (AAFCO) and various research institutions provide guidelines on the energy and mineral requirements of dogs as determined from research data they have generated or are able to access. Those requirements are generally presented in the form of a series of tables, each specific to a particular life stage or activity level, such as growth, resting, highly active, pregnant and lactating.
In addition to the NRC and AAFCO recommendations provided by those scientific organisations, a differing range of requirements is often advocated by individuals involved in specific activities such as greyhound racing. With respect to energy and calcium requirements, for example, some individuals providing feeding advice to the greyhound racing industry suggest a 30 kg racing greyhound requires 2,500 Kcal Metabolisable Energy and up to 6 – 8 g calcium per day7, but the basis for such recommendations are not always clear. Other sources propose that more active dogs need additional energy but not more calcium, phosphorus or vitamin D.5
Greyhound owners for a variety of reasons prefer to prepare home-made diets for their dogs, or use a combination of meat and commercial dry foods. In these instances it is important for trainers to understand the variation in nutrient content in all potential diet ingredients5. For example, chicken meat has a very low calcium: phosphorus ratio with low levels of iron and copper; diets high in cereals and grains contain higher levels of salts called “phytates” which can interfere with the absorption of calcium, zinc, iron, phosphorus5. Thus, diets with a high grain and phytate content (ie. lower quality foods) need a higher calcium and phosphorus content to provide the required levels of those minerals for absorption.
To ensure that a dog’s diet is complete and balanced, it is strongly recommended that the owners seek guidance from a veterinarian or other expert with specialised knowledge and experience in analysing the nutritional content of diets. Review of the diet components and quantities, ingredients and diet preparation protocol, along with a thorough physical assessment of the dog by a veterinarian, may highlight potential nutritional concerns and prevent avoidable illness.
Once the energy requirements of the dog have been determined, supplementation, where indicated, should be given on the basis of the calculated nutrient content of the ration base (be that raw meat or a combination of meat, commercial dry food, vegetable, dairy component etc.). The correct levels of vitamins and minerals must be determined in relation to the energy levels of the diet and with an understanding of the need for correct mineral balance5.
As determining the nutritional content of the meat portion of a greyhound’s diet is difficult Virbac and Vetsearch developed a product called Calci-D®, designed to balance the calcium and phosphorus ratio of meat and also adds the other important co-factors – Vitamins A and D, Magnesium and Zinc. Calci-D® is unique in that the amount added to the diet depends on the weight of meat fed, ensuring that your greyhound receives the correct balance of calcium and phosphorus in every meal.
In 2004, the late Allan Brown commissioned an article entitled: Caveat Emptor – Buyer Beware, which drew attention to the folly of buying the unknown. There is a huge variety of calcium supplements marketed for greyhounds and as we have just discussed, several factors that impact on the absorption and availability of calcium during digestion. It is essential that trainers and breeders only use supplements from reputable companies or nutritionists with a proven history of providing high-quality products.
Supplements should be manufactured at a facility operating under a Good Manufacturing Practice (GMP) licence. GMP licences are issued by Australian Government agencies and companies operating under GMP licence must ensure product is manufactured according to strict standards of quality and hygiene. This includes the use of high quality raw materials which will provide maximal nutritional benefit and avoid toxicities from potential impurities. It is also important that nutritional supplements are carefully formulated to avoid unwanted interactions between vitamin and mineral components and that the manufacturer has ensured the final product is stable over its stated shelf-life.
Calci-D® along with all the other Virbac and Vetsearch supplements are manufactured at GMP licensed sites, so the quality of the Vetsearch range can be guaranteed.
1. Gilette, R. L. (2002). Managing the greyhound racing surface – Part 1. Available from www.sportsvet.com [accessed 23rd March 2011]
2. Dyce, K.M., Sack, W.O., Wensing, C.J.G. (2002). Textbook of veterinary anatomy, 3rd Ed. Saunders, Philadelphia.
3. National Research Council (NRC): Animal Nutrition Series. (2006). Nutritional Requirements of Dogs and Cats. Washington D.C. National Academy Press, Chapters 7 and 15.
4. McDonald, P. et al. (2002). Animal Nutrition, 6th Edition. Pearson Education Limited, UK.
5. Hazewinkel, H.A.W. (2005). Consequences of nutrition on skeletal development in puppies. Iams Clinical Nutrition Symposium, Seville, Spain, January 29, 2005.
6. Zentek, J. (2008). Orthopedics – Growth Abnormalities: The Role of Nutrition. Proceedings of the Southern European veterinary Conference and Congreso Nacional AVEPA, 2008, Barcelona, Spain.
7. Kohnke, J. R. (2002). Feeding the racing greyhound. 497 – 501
|Your local Representative|