Brilliant weather draped in crisp, vivid colors signals the beginning of fall hunting and field trial season. Owners of sporting dogs optimistically set off with high expectations, but unless a dog is properly conditioned and nutritionally prepared, physical exhaustion, and stress could result in injuries or health problems.
“A certain amount of stress is good. It helps the body to be prepared to handle stress,” says Purina Nutrition Scientist Arleigh Reynolds, DVM, Ph.D. “Too much stress without time to recover affects a dog’s attitude, how quickly it fatigues, and its willingness to perform. It’s best to prepare a dog slowly and take time to see results.”
When stress takes a toll, injuries such as strained tendons and muscles, foot accidents, and broken bones, may be more common. Dehydration, diarrhea, vomiting, and infections may occur, and signs of physical fatigue and mental exhaustion are likely to be noticeable.
During the past 20 years, increased knowledge about how dogs use energy when they are working has provided nutritional insights that have led to the formulation of performance diets with higher levels of fat and protein and fewer carbohydrates. More recently, nutritionists have boosted levels of antioxidants to help minimize oxidative damage to cells during intense activity.
“We have gained tremendous understanding about the mechanics involved in providing energy to muscle cells,” says Francis Kallfelz, DVM, a James Law Professor of Medicine at Cornell University’s College of Veterinary Medicine. “Particularly, we have observed the importance of fast as an energy source and of protein in building lean body mass and maintaining structural integrity.”
“A dog uses its energy stores based on the activity is performs,” Reynolds says. “A dog performing a short intense sport, such as a 40-second sprit race, largely uses glycolytie (anaerobic) energy, whereas a dog involved in an endurance activity, such as Large Pack or Small Pack Option field trials, mostly burns oxidative (aerobic) energy. The energy for endurance sports may cycle between glycolytic and oxidative energy, pulling from all available fuel sources.”
The first burst of energy supplied to muscles comes from high-energy compounds; called phosphagens Adenosine tri-phosphate (ATP) and phosphocreatine (PC) are two of the most important phosphagens in muscles cells. Phosphagens provide the first 15 to 30 seconds of energy needed for jumping or starting a race. Since phosphagens are made of protein metabolism byproducts, phosphagens performance is hindered when there is a protein insufficiency.
Glycolytic energy is produced in the conversion of glucose to lactic acid in an anaerobic or non-oxygen requiring process. The metabolism of carbohydrates that takes place in producing glycolytic energy is considered a primary source of energy in working muscles during intense exercise lasting from two to seven minutes.
A well-conditioned dog may convert to an oxidized level of energy metabolism after two minutes. Oxidative energy provides the energy that sustains dogs during endurance activities. This aerobic system uses oxygen to burn whatever energy stores can be found in cells, predominantly fat since it is the most energy dense, but also glucose and protein.
In recent years, scientists have gained a better understanding about the stress that occurs during oxidative metabolism and how it affects a dog’s performance and contributes to injuries. Work or exercise involves an increase in oxygen consumption. Oxygen metabolism generates free radicals, also called reactive oxygen species, made up of unstable particles, such as peroxides or superoxides, which can injure cells by causing oxidative damage to lipids in cell membranes, proteins, and DNA.
“We know exercise causes an increase in the production of free radicals,” Reynolds says. “Performance dogs that fail to consume a diet that provides adequate antioxidants to offset free radical production may suffer from muscle stiffness, damage, and sub par performance. Repetitive endurance exercise causes greater oxidative stress because it involves a prolonged increase in oxygen consumption.”
One study of 24 healthy sled dogs evaluated the effect of repetitive endurance exercise on antioxidants. The study involved randomly placing dogs in either an exercise group that completed a 58 kilometer (35.96-mile) run on three consecutive days or in a control group that was housed in a kennel. “We found decreases in blood vitamin E concentration in the exercise group, “says Kenneth Hinchcliff B.V.Sc., Ph.D. professor of clinical sciences at the Ohio State University’s College of Veterinary Medicine. “This relates to a decrease in antioxidant capacity and an increase in fat peroxidation. It also can be an early indicator of skeletal muscle damage.”
A dog’s diet is the foundation that helps support its performance. For maximum efficiency, the diet should contain a highly digestible source of energy that is readily and rapidly available to muscle cells. The diet also should provide complete and balanced nutrition to help minimize inferior performance and stress-related illnesses.
Hardworking sporting dogs can hardly get enough fat. “A diet that skimps on fat will significantly contribute to a reduction in endurance and overall fitness,” says Kallfelz, who is a member of the National Research Council committee that is rewriting the nutritional requirements for dogs. “Performance dogs require a diet that contains an appropriately high level of fat and protein to meet demanding physical activities.
Because fat is more energy-dense, increasing fat concentration in a diet is the only way to increase energy density. Fat supplies 8.5 kilocalories of metabolizable energy per gram, whereas protein and carbohydrate provide 3.5 kilocalories per gram. Metabolizable energy is the energy ultimately available to a dog after fecal and urine losses.
“A performance diet should have meat with a highly digestible, quality protein source as its first ingredient,” Kallfelz says. Trace elements should be included in an appropriate amount to provide a safety margin during performance. For example, iron and copper deficiencies can lead to anemia. Zinc is involved in muscle contractions, and iodine aids with thyroid function. Selenium, along with vitamin E, is important in helping preserve muscle integrity and protect cells from oxidative damage.
Based in Alaska, where he evaluates the impact of nutrition on the performance of sled dogs, Reynolds has studied canine performance stress for 15 years. “The goal should be to maintain each dog’s ideal weight and body composition,” Reynolds says. “Dogs should be weighed regularly, and the diet adjusted as needed to maintain ideal body condition. A dog’s individual energy requirement and body condition score is the gold standard determining how much food to feed.”
To help a dog get off to a good start nutritionally, owners should begin feeding a performance diet several weeks-ideally from 8 to 12 weeks before training begins. This allows time for a dog’s metabolism to adapt and for nutritional reserves to build.
The timing of food administration also is important. Dogs that work hard with food in the gastrointestinal tract may experience impaired performance and gastrointestinal upset. Because the gastrointestinal tract and the muscular system both require a large blood supply while working, neither can function optimally if both try to work intensely at the same time.
Exercise often is associated with loose and even bloody stools. This condition often referred to as “stress diarrhea,” may be due to exercising while the gastrointestinal tract is processing a large meal. Stress diarrhea can often be improved or prevented if the dog has time to completely process a meal and defecate its remains before his next bout of exercise.
“Ideally, a dog should be fed after exercise, when it is completely cool. If a dog is fed too soon, there is a risk of bloat or torsion, particularly in large-chested breeds,” Reynolds says. These breeds also should not be allowed to consume a large volume of food or water following exercise.
Though a little stress is not harmful, too much stress may deplete protein and nutrient reserves, and also diminish immune competence. “Overtraining may cause too much stress,” Reynolds says. “When this happens, protein degradation occurs and muscle mass breaks down. A dog may quickly fatigue and become tired, which affects attitude and performance.”
Training techniques that overly emphasize endurance work or involve too little work to adequately strengthen muscles and tendons may result in injury or decreased performance. Successful training involves a series of graded and tolerable exercises for the purpose of improving ability. In comparison, repeated exercise during depletion may lead to cumulative stress or overtraining.
Both environmental and emotional stress may contribute to reduced athletic potential. Environmental stress includes temperature extremes, humidity, overcrowding, unsanitary kennels, exposure to infectious agents, parasites, contaminated water, and poor diet.
“Heat is the single, biggest negative factor,” Reynolds says. “Dogs don’t sweat, and though panting cools them, it is inefficient. Dogs have an intricate blood supply that goes straight to the head to cool the brain and keep the central nervous system working at the expense of making the body warmer.”
Unavailability of drinking water may contribute to dehydration. Proper hydration is important, although dogs also can drink too much water and become sick. Reynolds recommends taking along a squirt bottle and if possible, allowing a dog to drink a small amount of water every 10 to 15 minutes.
Emotional stress may result from competition and aggression among dogs, leading to injuries, poor nutrition, and chronic stress. Nervousness before a competition – during transport or placement in a holding pen – may deplete muscle glycogen stores and energy. In addition, it may cause uncontrollable panting, which can result in dehydration, respiratory illness, and diminished performance.
Reynolds suggests techniques for lessening emotional stress. “It may help to pair a nervous dog with one that is confident. Sometimes you can adjust for stress simply by working with the dog’s individual personality,” he says.
POST – SEASON TRANSITION
Once the hunting or field trial season is over it helps to progressively de-escalate a dog’s training and exercise. The diet also should be gradually reduced or transitioned to a quality maintenance food. Most important, a dog should continue to participate in light exercise and cross-training.
“If a dog’s primary sport involves running, you may want to take up walking or swimming, “Reynolds says. “It helps to do things that are fun. Ultimately you want a well-rounded athlete that is able to handle stress. This helps to keep a dog in top condition for next season.”