本文发表在 rolia.net 枫下论坛We've all had a dog of our heart, a companion with whom we'd like to spend the rest of our days, but even the longest-lived dog will enjoy only about a third of our life spans. In fact, most dogs don't live nearly as long as many other species. Why, we might ask, has nature decreed that our best friends in the animal kingdom die so young? The answer lies with the wolf.
Dogs are the direct descendants of wolves--sharing 99.9 percent of their DNA--and wolves have lived very dangerous lives from time out of mind, taking down well-armed prey with nothing more than their mouths. Under these perilous conditions, those wolves who matured young and bred early passed on their genes while those wolves who delayed reproduction did not. In this way, natural selection compressed the lives of wolves, and our dogs have inherited this fateful genetic legacy. They will probably never live as long as we do, yet we can extend their naturally brief lives by how we breed and care for them.
There's no better place to start than nutrition. Although geneticists recently discovered that dogs can digest carbohydrates better than their ancestor the wolf, veterinary researchers have also demonstrated that the amount of starch a dog eats determines how much its blood sugar spikes. If dogs eat too much starch, they can eventually suffer from diabetes and obesity. It's also been widely noted that consistently maintaining blood sugar levels at the low end of the normal range, and the concomitant low insulin levels that result, are associated with longer life spans whether you're a worm, a mouse, a dog, or a human.
These facts suggest that if want our dogs to live longer, we should keep their blood insulin levels low. However, one of the most commonly used ingredients in dry dog food is corn. Not only is corn rich in soluble carbohydrates, raising blood sugar levels in dogs quickly, it's also heavily sprayed, receiving 30 percent of all agricultural herbicides used in the U.S.
Instead of feeding corn to our dogs every day, we can choose dog food that is grain-free but still contains carbs in the form of vegetables, especially green leafy and yellow-orange ones, both of which have been shown to reduce the incidence of cancer in dogs. A well-rounded dog food should also contain a variety of high-quality protein, for although dogs can digest carbs, they're not vegetarians by choice. They're omnivores who thrive on an eclectic diet, and numerous studies have demonstrated that dogs on high-protein diets have more endurance and superior aerobic performance. Chicken, duck, lamb, pork, venison, bison, and fish, rotated periodically, are good choices.
Pet food manufacturers have begun to pay attention to these findings. They now offer a variety of kibbles as well as frozen and dried raw food that meet these criteria as well as having no artificial colors or carcinogenic preservatives. Such kibbles can be had for $500 per year to feed a 70-pound dog, about twice the $229 per year that surveys by the American Pet Products Association show the average American spends on dog food.
We can also hedge our bets about our dogs living longer lives by vaccinating them minimally. Vaccines, for as much good as they do, are not benign and can cause adverse reactions--everything from arthritis to fatal hemolytic anemia. As a result, the American Animal Hospital Association's Canine Vaccine Task Force now recommends that dogs be inoculated no more frequently than every three years with the four core canine vaccines: distemper, parvovirus, adenorvirus-2, and rabies.
A third strategy we can use to improve the health of our dogs is to clean up their home environment. Dogs, like children, are more sensitive to environmental pollutants because they're smaller than adult humans and their exposure is greater per unit of body weight. Instead of feeding them out of plastic bowls, which may contain endocrine-disrupting phthalates, we can provide them with bowls made from stainless steel or glass as well as with beds that don't use flame-retardant fillers since they, too, leach endocrine disruptors. Avoiding carpets finished with formaldehyde, a known carcinogen that takes up to a year to off-gas, is a wise idea and so is filtering tap water as it removes heavy metals, chlorine, and nitrates. Finally, we can purchase non-toxic dog toys and forego spraying herbicides on our lawns and trees.
When it comes time to spay or neuter our dogs, we should consider this decision carefully. Over the last decade an emerging body of evidence in the veterinary literature has shown that spayed and neutered dogs have more adverse reactions to vaccines than do intact ones and are more likely to be obese. In addition, spayed and neutered dogs have a higher incidence of urinary incontinence, endocrine dysfunction, and ACL injuries. Most worrisome, they're more susceptible to developing certain cancers, like bone cancer, bladder cancer, and hemangiosarcoma, a cancer of the blood vessels that is the leading killer of Golden Retrievers in North America.
There are safer alternatives to spaying and neutering. We can give female dogs a tubal ligation or a hysterectomy and male dogs a vasectomy. The reproductive result is the same as that achieved by spaying and neutering--no puppies--but because these procedures leave the ovaries and testes intact, the dog retains its beneficial sex hormones, which are important in forestalling or preventing many of these health conditions.
Of course, one of the best ways to enjoy more years with our dogs is to choose long-lived ones from the start. Unfortunately, many current breed standards, which emphasize human conceptions of canine beauty rather than fitness, do nothing but steal years from our dogs. Consider dogs who have been bred to have short muzzles, like Pugs, Pekingese, and Bulldogs. They can have trouble breathing and, unable to pant effectively, overheat easily. Or take German Shepherds, with their unnaturally low-slung rear ends. These dogs have a 60 percent chance of having osteoarthritis in their hips once they pass the age of two, whereas Labrador Retrievers, with their normal-looking rear ends, have only a 20 percent chance.
Those of us in the market for a new dog can avoid the entire issue of unhealthy breed standards by going to our local animal shelter and picking a well-formed, long-nosed, mixed-breed dog--one who can breathe easily and run well. Such mixed-breeds suffer from fewer genetic diseases and live up to 1.8 years longer than purebred dogs of equivalent weight.
But if we're really set on living with a purebred dog, we can do some research to safeguard its future health. We can check to see that its breeder has done all the orthopedic and DNA health screenings appropriate for the breed, and we can temper our enthusiasm for a particular breed with sober reflection upon its documented longevity. For example, the average life span of Irish Wolfhounds is only 6.5 years. Bernese Mountain Dogs live between seven and eight years, and 75 percent of Saint Bernards are dead by the age of ten. By contrast, Australian Shepherds, Border Collies, Labrador and Golden Retrievers, Beagles, Dachshunds, and Standard Poodles all live about twelve years.
We can push every one of these canine life spans upwards by tracing the pedigree of a prospective litter back through time with the help of online data bases. By then calling the breeders of the litter's ancestors we can get an idea of how long they lived and what they died of, noting where longevity lies. Some Labrador Retrievers lines, for instance, live an average of only twelve years whereas some live fifteen. Calculating a prospective litter's coefficient of inbreeding with a downloadable software program (http://www.pedfast.com/) is also worth doing. Aim for coefficients of inbreeding of less than 6 percent. Such dogs have fewer chances of receiving two copies of the recessive genes that can cause fatal diseases. Finally, we can visit the kennel of our chosen breeder to appraise the conditions in which our new pup will be nurtured during its all-important first weeks of life. One doesn't have to be a USDA inspector to notice cleanliness, care, and love.
If, despite all these efforts, our dogs become seriously ill, we can then initiate treatments that were unimaginable just a few years ago. Dogs with lymphoma, for example, can be given a bone marrow transplant, the same standard of care offered to humans; bioartificial livers, cultured from a dog's own cells, have been successfully implanted in Beagles with liver failure; and in the very near future magnetically tagged nanoparticles will be able to deliver anticarcinogenic antibodies precisely to tumors.
It's been several thousand years since Odysseus returned to Ithaca and shed a tear for his beloved Argos, whom he had left as a young dog twenty years before and who had become so crippled that he couldn't rise and greet him. All of us who have loved a dog know the feeling. We will always lament their too-short lives, but at least we now have more science-based strategies that can increase our time together.
Ted Kerasote is the author of the new book Pukka's Promise: The Quest For Longer-Lived Dogs.更多精彩文章及讨论，请光临枫下论坛 rolia.net
Dogs are the direct descendants of wolves--sharing 99.9 percent of their DNA--and wolves have lived very dangerous lives from time out of mind, taking down well-armed prey with nothing more than their mouths. Under these perilous conditions, those wolves who matured young and bred early passed on their genes while those wolves who delayed reproduction did not. In this way, natural selection compressed the lives of wolves, and our dogs have inherited this fateful genetic legacy. They will probably never live as long as we do, yet we can extend their naturally brief lives by how we breed and care for them.
There's no better place to start than nutrition. Although geneticists recently discovered that dogs can digest carbohydrates better than their ancestor the wolf, veterinary researchers have also demonstrated that the amount of starch a dog eats determines how much its blood sugar spikes. If dogs eat too much starch, they can eventually suffer from diabetes and obesity. It's also been widely noted that consistently maintaining blood sugar levels at the low end of the normal range, and the concomitant low insulin levels that result, are associated with longer life spans whether you're a worm, a mouse, a dog, or a human.
These facts suggest that if want our dogs to live longer, we should keep their blood insulin levels low. However, one of the most commonly used ingredients in dry dog food is corn. Not only is corn rich in soluble carbohydrates, raising blood sugar levels in dogs quickly, it's also heavily sprayed, receiving 30 percent of all agricultural herbicides used in the U.S.
Instead of feeding corn to our dogs every day, we can choose dog food that is grain-free but still contains carbs in the form of vegetables, especially green leafy and yellow-orange ones, both of which have been shown to reduce the incidence of cancer in dogs. A well-rounded dog food should also contain a variety of high-quality protein, for although dogs can digest carbs, they're not vegetarians by choice. They're omnivores who thrive on an eclectic diet, and numerous studies have demonstrated that dogs on high-protein diets have more endurance and superior aerobic performance. Chicken, duck, lamb, pork, venison, bison, and fish, rotated periodically, are good choices.
Pet food manufacturers have begun to pay attention to these findings. They now offer a variety of kibbles as well as frozen and dried raw food that meet these criteria as well as having no artificial colors or carcinogenic preservatives. Such kibbles can be had for $500 per year to feed a 70-pound dog, about twice the $229 per year that surveys by the American Pet Products Association show the average American spends on dog food.
We can also hedge our bets about our dogs living longer lives by vaccinating them minimally. Vaccines, for as much good as they do, are not benign and can cause adverse reactions--everything from arthritis to fatal hemolytic anemia. As a result, the American Animal Hospital Association's Canine Vaccine Task Force now recommends that dogs be inoculated no more frequently than every three years with the four core canine vaccines: distemper, parvovirus, adenorvirus-2, and rabies.
A third strategy we can use to improve the health of our dogs is to clean up their home environment. Dogs, like children, are more sensitive to environmental pollutants because they're smaller than adult humans and their exposure is greater per unit of body weight. Instead of feeding them out of plastic bowls, which may contain endocrine-disrupting phthalates, we can provide them with bowls made from stainless steel or glass as well as with beds that don't use flame-retardant fillers since they, too, leach endocrine disruptors. Avoiding carpets finished with formaldehyde, a known carcinogen that takes up to a year to off-gas, is a wise idea and so is filtering tap water as it removes heavy metals, chlorine, and nitrates. Finally, we can purchase non-toxic dog toys and forego spraying herbicides on our lawns and trees.
When it comes time to spay or neuter our dogs, we should consider this decision carefully. Over the last decade an emerging body of evidence in the veterinary literature has shown that spayed and neutered dogs have more adverse reactions to vaccines than do intact ones and are more likely to be obese. In addition, spayed and neutered dogs have a higher incidence of urinary incontinence, endocrine dysfunction, and ACL injuries. Most worrisome, they're more susceptible to developing certain cancers, like bone cancer, bladder cancer, and hemangiosarcoma, a cancer of the blood vessels that is the leading killer of Golden Retrievers in North America.
There are safer alternatives to spaying and neutering. We can give female dogs a tubal ligation or a hysterectomy and male dogs a vasectomy. The reproductive result is the same as that achieved by spaying and neutering--no puppies--but because these procedures leave the ovaries and testes intact, the dog retains its beneficial sex hormones, which are important in forestalling or preventing many of these health conditions.
Of course, one of the best ways to enjoy more years with our dogs is to choose long-lived ones from the start. Unfortunately, many current breed standards, which emphasize human conceptions of canine beauty rather than fitness, do nothing but steal years from our dogs. Consider dogs who have been bred to have short muzzles, like Pugs, Pekingese, and Bulldogs. They can have trouble breathing and, unable to pant effectively, overheat easily. Or take German Shepherds, with their unnaturally low-slung rear ends. These dogs have a 60 percent chance of having osteoarthritis in their hips once they pass the age of two, whereas Labrador Retrievers, with their normal-looking rear ends, have only a 20 percent chance.
Those of us in the market for a new dog can avoid the entire issue of unhealthy breed standards by going to our local animal shelter and picking a well-formed, long-nosed, mixed-breed dog--one who can breathe easily and run well. Such mixed-breeds suffer from fewer genetic diseases and live up to 1.8 years longer than purebred dogs of equivalent weight.
But if we're really set on living with a purebred dog, we can do some research to safeguard its future health. We can check to see that its breeder has done all the orthopedic and DNA health screenings appropriate for the breed, and we can temper our enthusiasm for a particular breed with sober reflection upon its documented longevity. For example, the average life span of Irish Wolfhounds is only 6.5 years. Bernese Mountain Dogs live between seven and eight years, and 75 percent of Saint Bernards are dead by the age of ten. By contrast, Australian Shepherds, Border Collies, Labrador and Golden Retrievers, Beagles, Dachshunds, and Standard Poodles all live about twelve years.
We can push every one of these canine life spans upwards by tracing the pedigree of a prospective litter back through time with the help of online data bases. By then calling the breeders of the litter's ancestors we can get an idea of how long they lived and what they died of, noting where longevity lies. Some Labrador Retrievers lines, for instance, live an average of only twelve years whereas some live fifteen. Calculating a prospective litter's coefficient of inbreeding with a downloadable software program (http://www.pedfast.com/) is also worth doing. Aim for coefficients of inbreeding of less than 6 percent. Such dogs have fewer chances of receiving two copies of the recessive genes that can cause fatal diseases. Finally, we can visit the kennel of our chosen breeder to appraise the conditions in which our new pup will be nurtured during its all-important first weeks of life. One doesn't have to be a USDA inspector to notice cleanliness, care, and love.
If, despite all these efforts, our dogs become seriously ill, we can then initiate treatments that were unimaginable just a few years ago. Dogs with lymphoma, for example, can be given a bone marrow transplant, the same standard of care offered to humans; bioartificial livers, cultured from a dog's own cells, have been successfully implanted in Beagles with liver failure; and in the very near future magnetically tagged nanoparticles will be able to deliver anticarcinogenic antibodies precisely to tumors.
It's been several thousand years since Odysseus returned to Ithaca and shed a tear for his beloved Argos, whom he had left as a young dog twenty years before and who had become so crippled that he couldn't rise and greet him. All of us who have loved a dog know the feeling. We will always lament their too-short lives, but at least we now have more science-based strategies that can increase our time together.
Ted Kerasote is the author of the new book Pukka's Promise: The Quest For Longer-Lived Dogs.更多精彩文章及讨论，请光临枫下论坛 rolia.net