Mineral and vitamin additives

If you are considering adding any supplements to your dog’s diet, understand their purpose first.

Calcium

Most good quality dry foods are heavily supplemented with sufficient calcium, so no supplementation is needed if feeding the correct proportions of dry food to meat. If fact, there is often too high a level of vitamin D in many of our dry foods, which in turn increases absorption of the calcium in the diet.

A higher quantity of meat in the diet, however, provides more phosphorus than is necessary, particularly if the high-density phosphorus meats such as kidney, liver and heart are fed. High phosphorus levels in the diet inhibit calcium absorption; to counter this lowered absorption, more calcium may be needed to balance the diet.

The availability of calcium in the diet of rapidly growing puppies is very important in the correct development of bone structure. Puppy dry foods usually have particularly high levels of calcium added, as do cereal-based dry foods, where absorption of calcium is much lower than with meat-based dry foods.

Too much calcium in the diet can be seen particularly in puppies of breeds with short, upright pasterns when fed high-cereal puppy dry foods in cold weather.

Due to the cold, the tendons of the wrists contract, causing a knuckling forwards and/or sideways (this is known as carpal luxation). The wrists may need to be taped for several days and the diet corrected – taking the puppy off high vitamin D and cereal-based puppy dry foods and increasing the percentage of meat in the diet for a few days usually corrects the problem as quickly as it developed.

Too little calcium in the diet has been a considerable problem in the past, but with the improvements to dry foods over the past 15–20 years, cases of affected puppies have become very rare. However, with the increasing number of people trying ‘homemade diets’, we are starting to see cases of these deficiencies reappearing.

The lack of calcium (and other minerals) available in homemade diets can result in nutritional secondary hyperparathyroidism, also known (incorrectly) as ‘rickets’. The bone structure of affected puppies is so weak that they cannot stand and many will drag their hindquarters.

These puppies often have multiple hairline fractures and are in extreme pain unless handled very gently. On X-ray, the bones are ghostly. The condition is reversible over several weeks if the dietary problems are corrected early on.

Vitamin D

Manufactured by the dog through exposure to sunlight, vitamin D helps calcium absorption, but too much can cause the body to start reabsorbing calcium from the bones. If the weather is bright and sunny, it is unnecessary to add any extra vitamin D.

During prolonged periods of overcast or wet weather, young growing dogs may go down on their pasterns. This can be from a lack of exposure to sunlight; during these periods, a vitamin D supplement may be given as often as twice weekly if absolutely necessary.

Sardines in oil are a user-friendly source of extra vitamin D if needed; as the vitamin D available from the sardines is not too concentrated, you are less likely to over-compensate than if using supplements.

Zinc

An essential component of all diets, zinc is the most common mineral deficiency seen in dogs today. Zinc is essential to many enzymes and pathways throughout the body, and is also essential to reproductive health, skin and coat health and ligament strength, to name a few critical areas.

Cereal-based dry foods are low in zinc and, where extra zinc is added, other components in the diet often interfere with its absorbtion. Chelated zinc products, which have zinc molecules bonded to proteins, have very high absorption rates.

Very heavy-boned puppies or breeds may occasionally need small amounts of zinc added to their diet if the feet and pasterns suddenly change. Use low doses first and if you see improvement, reduce the dose and then stop.

Only use low doses of any supplement if, and only, when needed and if there is no improvement within a week, talk to your veterinarian about where the diet may be lacking.

Vitamin C

As a dog’s liver is capable of synthesising vitamin C, it is not an essential additive to the diet. Vitamin C assists in the cohesion of structural tissues, so it affects bone cell maturation in growing dogs.

While there is no current indication for the addition of vitamin C to dog diets, it can be given, but preferably only in moderation – 250 mg daily is quite enough for a growing puppy of a larger breed. Low-dose vitamin C may be of benefit in fast-growing puppies that are sore in the bones and joints.

Multi-vitamin

Most of these are fairly good provided they are not given in vast quantities. Multi-mineral supplements can supply trace elements that may be lacking in some cereal-based diets, but many of the vitamins and minerals are quite readily available in a well-balanced diet.

Adverse conditions, such as drought, can create a deficiency of certain trace elements in cereals, and heavy work, lactation and stress situations can increase the requirements for many minerals and vitamins.

Dr Karen Hedberg BVSc is a veterinarian at North Richmond Veterinary Hospital.