Practical nutrition for working dogs

Introduction

Although the number of working dogs that will be presented to the average small animal practicing veterinarian may be low, it remains important to know how to advise their owners, as these dogs have very specific nutritional requirements. In order to give an overview of the different factors that should be taken into account when addressing this issue, this article will briefly discuss how muscle physiology functions during strenuous activity, and then present a summary of the requirements for the different types of working dog. It can be helpful to categorize these dogs as follows;

• Low-intensity, high-duration exercise (e.g., endurance dogs)
• Moderate-intensity, moderate to high-duration exercise (e.g., police dogs, hunting, search and rescue, service dogs)
• High-intensity, short-duration exercise (e.g., sprinting, agility and weight pulling)

It is essential to take into account not only the actual nutritional requirements for these animals, but also to consider other management factors that can be applied in order to help these canine athletes function to the best of their ability.

Energy sources during exercise

During exercise, muscles requires ATP (adenosine triphosphate) as fuel. This can be obtained from different sources, and can be both from within the muscle (endogenous sources) and from other organs (exogenous sources). When oxygen is available, aerobic metabolism (oxidation of glycogen, fatty acids and amino acids) will occur in the cellular mitochondria, whereas in the absence of oxygen anaerobic metabolism will take place in the cytoplasm (Figure 1). Which fuel source will be used is determined by the type and the intensity of the work, and the conditioning and nutritional status of the working dog.

There are four important energy-generating pathways: creatine phosphate (Cr-P) and glycolysis, which occur in the absence of oxygen, and carbohydrate oxidation and fat oxidation, which can only take place when oxygen is available. The first two methods can generate ATP from endogenous storage in the muscle during the first seconds (Cr-P) or minutes (glycogen) of activity, and are thus very important for short, high-intensity exercise such as sprinting and weight pulling. Complete oxidation of carbohydrates and fatty acids will supply the muscles with energy over a prolonged period of time (hours) and are thus the most important energy sources for low to moderate-intensity exercise such as hunting, agility, police work (Figure 2) and pulling sleds.

During exercise, negative byproducts are also produced, namely heat, acids (CO₂ and lactic acid) and free radicals. A dog will disperse the heat by panting, whilst the aerobically produced CO₂ is lost through the renal system or the respiratory tract. Anaerobic production of lactic acid will limit muscle functionality very quickly, because a suboptimal muscle pH will inhibit muscle enzymes. When a dog is no longer able to lose excess heat by panting, its body temperature will rise, and muscle functionality will decrease. Training will not only increase the endogenous storage capacity of the muscle, it will also enhance the number of mitochondria in muscle cells and the overall lung capacity, which in combination will increase the dog’s capacity to perform exercise.

How should a working dog be fed?

The amount and type of food a working dog should receive depends on various different elements. These include the work intensity and duration, but also environmental factors such as the ambient temperature (not only throughout the work period but also during rest/recovery), the terrain being worked, and the dog’s temperament. Although consideration may be given to predicting caloric expenditure during training and exercise by assessing the speed and intensity of the work involved, it is important to also take into account the distance the dog will travel during an exercise period.

Whilst there are NRC (National Research Council) guidelines available that can be used as a starting point, each animal should be considered as an individual case. The 9 point Body Condition Score (BCS) is the main physical benchmark when calculating the amount of food to be fed. Dogs that perform low- or moderate-intensity exercise should be kept at a BCS of 4 or 5, whereas dogs performing high-intensity exercise are usually kept at a BCS 3 or 4. Dogs in the high- and moderate-intensity classes usually do not require more than twice the recommended MER (Maintenance Energy Requirement) for pet dogs 1, whereas dogs in the low-intensity category may require up to 6 x MER, for example during a racing season. This variability in energy requirements also has an impact on the main energy sources that should be identified when advising a specific diet. Where dogs in the high and moderate classes require energy both from digestible carbohydrates and fats, dogs that undertake low-intensity activities will require mainly fat as an energy source and negligible amounts of digestible carbohydrates 2. In contrast to other species of athletes (humans, horses), where the rapid reloading and replenishing of glycogen stores following a workout is proven, studies in dogs have resulted in conflicting results. However, from knowledge of muscle physiology it can be assumed that dogs in the high- and moderate-intensity categories will use some of their glycogen stores during exercise that (ideally) will be replenished as efficiently as possible. Therefore, it is advisable that these dogs have some of their energy requirement supplied as digestible carbohydrates. Dogs subject to high-intensity exercise should get 40% or more of their calories from the nitrogen free extract (NFE) section of their diet (i.e., the fraction that contains the sugars and starches), whilst dogs in the moderate-intensity category should get 15-40% of calories from the NFE. Keep in mind that, in combination with the correct amount and type of training, these glycogen stores can be increased, thus improving performance by delaying the onset of acidosis.

Sled dogs are perhaps in a class of their own when it comes to nutrition (Figure 3). As can be imagined, the amount of food that can be physically consumed by a sled dog on a daily basis is a limiting factor, thus more than 60% of the energy for these animals should be supplied as fat, which has a high energy density. Because of this, and also because of financial restraints, some owners will prepare a home-produced diet for their sled dogs, which may include raw foodstuffs. The pro and cons of such diets have been extensively reviewed elsewhere in the literature and will not be discussed further here, although the risk of bacterial contamination (e.g., Salmonella, Campylobacter spp.) should not be ignored. Emphasis should always be put on balancing these diets with appropriate addition of a vitamin/mineral/trace element premix in order to support performance.

Working dogs also have differing protein requirements. During training, and certainly during performance, protein turnover is increased, although to what extent is difficult to quantify. However, protein recommendations for the different intensity categories are not dissimilar: diets for dogs that do high-intensity and short-duration moderate-intensity work should contain between 24-28% protein (DM) from high-quality protein sources, whereas diets for animals subject to long-duration, moderate-intensity or low-intensity exercise should contain > 30% protein (DM) 3. As a general rule, the protein supplied should be sufficient to meet the dog’s anabolic requirements with sufficient non-protein energy nutrients (fat and NFE) given to meet its energy requirements.

What about other factors?

Given the importance of the respiratory tract and the renal system to keep the body functioning optimally during and after exercise, the significance of water amount and supply cannot be overlooked. As a general rule fresh drinking water should be made available at all times whenever possible, so ideally before, during and after exercise. The one exception to this rule is with sprint dogs, where water is sometimes withheld before the race to decrease ballast.

Another important consideration is the digestibility of the food. The higher the digestibility, the less food is required to supply dogs with their energy requirements and the less fecal bulk is produced. A dry matter digestibility of > 80% is therefore advisable. In addition, and as discussed earlier, with certain high- and moderate-intensity activities part or even the entire glycogen storage may be depleted during exercise, so for dogs performing in multi-day events, a carbohydrate boost post-exercise could help replenish these stores more quickly.

As with every process in the body, free radicals are produced during exercise. Normally these are neutralized by the available antioxidants (e.g., vitamin E, vitamin C and selenium) but when free radical production is excessive, oxidative stress will result. In human athletes, this is known as chronic muscle disease or overtraining. When advising antioxidant supplementation, it is important to keep in mind that high doses of a single antioxidant may actually have a pro-oxidant effect and should therefore be avoided 4. Using a lower dose of a multi-nutrient antioxidant is always to be preferred, as vitamin E, Vitamin C and selenium work synergistically. Table 1 offers recommended guidelines for the common antioxidants that can be added to the diets for working dogs, although as when considering addition of a multivitamin/mineral premix, a blanket recommendation to supplement without consideration of an animal’s base diet is never a good idea.

(Table 2) offers a brief summary of the various factors that should be considered when advising the owner of a working dog as to their nutritional requirements.

How about a puppy with working dog ambitions?

A brief mention of puppies that are scheduled to be working dogs is appropriate, as environmental and nutritional factors will greatly influence the future athletic performance of a growing dog. Above all, these animals should be fed a puppy diet designed specifically for their expected adult weight; so for example large breed puppies require a diet with less calories and calcium that allows them to maintain a lean body weight at all times, in order to avoid them gaining excess weight or growing too fast. Failure to do so may result in osteochondrosis lesions, skeletal abnormalities and hip dysplasia. High-intensity training for puppies should be avoided until skeletal growth is complete, but low-intensity/impact training can be undertaken during dynamic growth.

In addition, at least one study has shown that beneficial effects on early performance and behavior training can be achieved by modulating the uptake of the omega-3 fatty acid DHA (docosahexaenoic acid) in puppies up to 1 year of age. However, more work needs to be done in this area, as the diet used in this study contained other additional nutrients that could positively affect learning and memory (e.g., vitamin E, taurine, choline and L-carnitine) 5.

It is important to appreciate that working dogs will not only vary in their dietary requirements depending on the type of work that they do, but that many extrinsic factors also come into play. The veterinarian should take an individual approach to each dog and make recommendations after a thorough assessment of the work undertaken, as well as considering the physical and emotional aspects of the animal.