Nutritional requirements of the dog: work

The working conditions of dogs are extremely varied and, as for humans, can range from pure sprints to marathons. Greyhounds run at a speed of 60-70 km/hour for 30-50 seconds, while sled dogs at the Pole cover from 50 to 80 km a day dragging loads of almost 50 kg for periods of 6-8 weeks in temperatures close to -40°C. Working dogs constitute a very well represented category; it has been estimated that there are least one million owners and breeders of working dogs in Italy alone._⁴

Before entering into the details of the nutritional requirements of working dogs, it is worth remembering that the energy released following the breakdown of foods is not used directly for the work of muscles; it serves to produce the only chemical molecule that can be used by muscle cells to contract: adenosine triphosphate (ATP). The energy available to muscles is produced during the hydrolysis of ATP into adenosine diphosphate (ADP) and inorganic phosphorus.

The reserves of ATP must be continuously replaced; there are various pathways through which this can occur. In a chronological sense, and schematically, there are three stages of energy expenditure, which condition the physiological, metabolic, haematological and endocrinological responses of the animals.

The first stage, the so-called creatine phosphate (alactic) anaerobiosis, lasts from 5 to 30 seconds and involves the use of muscle ATP and does not seem to be influenced by external factors such as diet or training.

The second stage, lactic anaerobiosis, occurs in 2 to 3  minutes and uses muscle glycogen and blood glucose. Lactic acid, one of the main factors limiting effort, is produced in this stage. In extreme cases the accumulation of lactic acid can cause severe damage to the muscle tissue through:

• osmosis-induced muscle oedema, accompanied by an increase in the haematocrit and a state of apparent dehydration;
• predisposition to myoglobinuria (the presence of myoglobin in the urine, caused by the lysis of muscle cells).

The third stage, aerobiosis, also exploits glucose and glycogen, but above all the non-esterified fatty acids (NEFA) and, in part, amino acids; this process occurs in the presence of oxygen and requires at least 3 minutes before it can intervene effectively. Oxidation of fatty acids constitutes the main source of muscle energy in the case of long-lasting efforts of medium or light intensity. This metabolic pathway is favoured by:

• suitable training;
• a cold climate;
• fat-rich rations of food.

The dog obtains most of its energy from adipose tissue and, unlike man, can meet its own energy needs with a diet free of sugars._¹

The mechanical yield of the energy produced in muscles is not high (being about 25%); indeed, three-quarters of the energy produced is transformed into heat. Thus, increasing intensity of muscle work is accompanied by a rise in body temperature and increases in body temperature varying from 1 to 3°C have been recorded in dogs undergoing physical effort._^5-7 In the presence of high ambient temperatures, marked atmospheric humidity and greater thermal isolation of the skin (long, thick hair, subcutaneous fat) the rise in body temperature is accelerated. Ambient temperatures above 25°C, with a humidity over 75%, are potentially harmful to dogs that do not have access to water. The heat developed by the muscles is dispersed by the dog principally through panting, which enables water to evaporate from the nose and mouth, and secondarily through the skin, by radiation and convection (Fig.1).

If the dog cannot maintain its body temperature below 42 °C, its performance decreases rapidly because the excess heat must be eliminated through the body surface. In this case the peripheral blood supply increases at the cost of the blood supply to the muscles. Large losses of water decrease the amount of intravascular water causing an increase in the concentration of the blood.

For all these reasons, for the purpose of immediate performance, the intake of water is more important than further amounts of energy.

The energy requirements of the working dog or canine athlete are the sum of the maintenance energy requirement and the energy needed for the work that the dog undertakes. The work requirements are influenced by many variables and in order to be able to estimate them some parameters need to be known: the duration and type of work, the environmental conditions in which the work takes place and the degree of training.

In trained animals, the speeds that a medium-sized dog can reach are:

• walking: 4-5 km/h
• trotting: 8-12 km/h
• galloping: 12-16 km/h

These speeds can be maintained for 6 to 8 hours or more, with pauses and possible changes in gait. Racing dogs can even reach a speed of 70 km/hour, although only for a few minutes; pointing dogs, in competitions, can trot and gallop at much faster speeds than those listed above, but only for limited periods. The faster gaits are obviously associated with higher energy expenditure; thus, for an equal body weight and duration of work, a galloping dog will use from three to five times more energy than a walking dog.

The speeds reported above are those for the movement on the level; obviously they change considerably depending on the slope of the ground_^2,3 which can, therefore, become another variable that must be evaluated when calculating energy requirements. A dog hunting on a mountain will always be at a gradient, often very tasking. For example, it is thought that 20 minutes’ work on the level does not increase body temperature, whereas with a gradient of 12% the temperature rises to about 40°C and with a gradient of 22% the temperature can reach almost 42°C._⁴ The increase in body temperature considerably reduces the work yield and, beyond a certain limit, becomes life-threatening to the animal. If the ambient temperature in which the dog works is high, the animal will have a greater energy expenditure because of the need to implement mechanisms of heat dispersion. The ambient humidity acts as an aggravating factor and the temperature perceived can be higher in conditions of marked humidity. Finally, another variable to consider is the asperity of the surface, which, when marked, hampers running and walking, forcing the dog to make further efforts and also putting the locomotor apparatus (bones and tendons) at risk. A classic example is hunting in areas dense in high vegetation in which the dog is forced to “jump” continuously. Running on soft, deep snow is also exhausting. The energy expenditure for jumping has been calculated to be 0.008 kcal ME/kg of body weight/jump._⁴

In practice, the variables that are currently considered in the calculation of energy requirements of working dogs and canine athletes are mean speed (determined by the type of work the dog undertakes), work duration and body weight of the dog. Table 1 presents the parameters used.

Table 1. Energy requirements of a medium-sized dog in relation to various types of effort (kcal ME/kg body weight)._¹

As far as concerns the requirements for other nutrients, well-established minimal levels for working animals are lacking, mainly because of the large variety of working conditions of the animals. The main indications in the literature concern the requirements for water, carbohydrates, proteins and antioxidants. Table 2 summarises the main indications according to the type of activity.

Table 2. Indications concerning nutrient requirements in different working conditions (PUFA: polyunsaturated fatty acids; NfE: nitrogen-free extracts; ME: metabolisable energy)._⁸

Among the nutrients listed in Table 2, particular mention should be made of polyunsaturated fatty acids and vitamin C. As far as concerns the former, it is important to remember that these play an important role in the composition of the membrane of neurones and that a study in 2003_⁹ showed that the degree of saturation of the fats can affect the olfactory capacity of dogs. For vitamin C, on the other hand, it is worth recalling that maintenance doses of the nutrient are not considered because dogs, unlike humans, are able to synthesise this vitamin._¹⁰ However, in working dogs, given the increased need of antioxidant substances, integration with the amounts indicated in the table could be useful with the aim of improving indicators of oxidative stress, in analogy to what has been demonstrated in horses._¹¹

In summary, the nutritional requirements of working dogs are probably those least known at present, both because of the limited availability of studies on the physiology of exercise carried out “in the field” in the various disciplines and because of the obvious difficulty in quantifying the many variables that strongly affect energy expenditure. It is to be hoped that in the future the advent of new technologies_^2,3 will be of help in the objective quantification of all the variables so as to be able to determine, with a certain precision, the nutritional requirements of this group of dogs as well.

References

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3. Lasagna A. La Pernice Bianca Lagopus mutus helveticus (Thienemann 1829) in Valle d’Aosta. Indagine preliminare sullo status delle popolazioni (2009). Assessorato Agricoltura e Risorse Naturali  – Dipartimento Risorse Naturali e Corpo Forestale – Direzione Flora, Fauna, Caccia e Pesca.
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