Questions benefits of high carbohydrate content in canine diets

I read the article “Role of carbohydrates in the health of dogs”¹ with interest. However, I worry that the article could be seen as attempting to justify feeding diets containing carbohydrate contents similar to those commonly found in commercial pet foods (ie, 30% to 60% on a dry-matter basis). I agree with the authors that, “Dogs do not have a dietary requirement for carbohydrate, except during pregnancy and lactation.”¹ In my opinion, then, it is incumbent on pet food manufacturers to convincingly demonstrate that carbohydrate contents this high are healthful. In my opinion, conclusive evidence of this is lacking.

Of special concern to me is the authors’ treatment of evolutionary diets (ie, diets based on the presumed diets of the ancestral wolves from which modern-day dogs and wolves are descended). I was especially disappointed that the section entitled “Carbohydrate Content in Evolutionary Diets” did not address the contents of evolutionary diets. Instead, most of this section reviewed a study² that used comparative genetics to show that dogs can digest and absorb starch more efficiently than wolves do. Unfortunately, that study sheds little light on the ideal diet for dogs since the ability to process specific nutrients does not mean that a diet rich in them is health promoting. Humans can digest and absorb ethanol and sucrose, but it does not follow from this that we would benefit from a diet rich in those nutrients. This section concludes by mentioning that wolves have consumed diets consisting of up to 50% plant matter. Although this may be true, plant matter is not the preferred diet of wolves, and the fact that wolves occasionally consume substantial amounts of plant material when prey is unavailable does not prove that carbohydrates are a desirable diet component.

A comprehensive review³ of 50 diets of wild wolves reported in the literature found that, on average, the protein-fat-carbohydrate profile of wolves is 54:45:1% of metabolizable energy. This percentage of carbohydrates is very different from National Research Council guidelines for dogs, which allow up to 78.8% carbohydrate.¹ Furthermore, the authors of that review³ state that, “The nutritive characteristics of commercial foods differ in several aspects from the dog's closest free-living ancestor in terms of dietary nutrient profile and this may pose physiological and metabolic challenges.”

Although it is not certain that evolutionary diets are ideal for domestic dogs, in my opinion, presenting a more complete view of this concept would have enhanced this report.

Doug Knueven, DVM

Beaver Animal Clinic Beaver, Pa

The authors respond

We thank Dr. Knueven for taking the time to respond to our review and welcome the opportunity to provide our thoughts.

This review was intended to present current knowledge regarding carbohydrates and nutrition in dogs. We agree that there is a lack of evidence concerning the health benefits of either high- or low-carbohydrate diets. Dogs live a very different lifestyle from (eg, they are mostly neutered and frequently live a relatively inactive indoor life) and have a longer life span than wolves. There is insufficient evidence that the diet of wolves provides optimal nutrition for dogs.

Long-term trials are needed to investigate the effects of carbohydrates on canine health. Unfortunately, these trials are expensive and time-consuming. As highlighted in our review, when given the choice, dogs self-selected for a diet with 36% metabolizable energy from carbohydrates when differences in flavor were masked.¹ Although it is believed that these diets were selected on the basis of physiologic requirements, it is unknown whether self-selection for macronutrient balance provides a diet that supports optimal health.

The role of protein in canine health was outside the scope of this review, but relevant to Dr. Knueven's comments. The consequences of a high-protein diet on long-term health of dogs are unknown. In humans, high protein intake may lead to protein fermentation in the gut and the production of harmful metabolites that have been linked to renal disease and colorectal cancer.^2,3 Reduced fecal quality has been reported in dogs fed a high-protein diet.⁴ This topic warrants further investigation in dogs. Additionally, some high-protein ingredients are also high in fat, which may create other health concerns, including pancreatitis and obesity.

It is estimated that globally, 9 billion people will need to be fed by 2050. Therefore, food sustain-ability is a critical consideration. The United States has the largest pet population globally, with > 163 million dogs and cats.⁵ This is equivalent to a country of approximately 690 million people in terms of animal-derived energy consumed. Meat production requires more energy, land, and water and has a greater environmental impact, compared with production of plant-based foods.⁶ Thus, how pets are fed has a considerable environmental impact. Protein is an economically and environmentally expensive macronutrient. As discussed in our review, carbohydrates are a more efficient energy source because nitrogenous waste does not need to be excreted. Protein is used for important processes, such as hormone synthesis and tissue repair, but once an animal's amino acid requirements are met, excess protein is used for energy or converted to fat for storage. Therefore, if carbohydrates can be used to meet energy requirements without negative health consequences, they represent a more sustainable energy source for pets.

Current research does not suggest that the health of dogs suffers when they are fed a moderate quantity of carbohydrates. Similarly, there is no evidence that a diet similar to that eaten by wolves would improve their health. The topic of optimal macronutrient balance for dogs, especially taking into account various breeds and sizes, is of interest to many animal scientists and veterinarians and certainly requires more research.

Alexandra Rankovic, MSC

Adronie Verbrugghe, DVM, PhD

Department of Clinical Studies Ontario Veterinary College University of Guelph Guelph, ON, Canada

Jennifer Adolphe, PhD

Petcurean Chilliwack, BC, Canada

Continued discussion on banning cat declawing

I want to thank Dr. Neunzig for his recent letter¹ regarding bans on cat declawing, which brings this topic into the open for discussion. The difficulty with the topic of declawing is that, in the past, most statements about the anatomy of the distal phalanx in cats, postoperative complications of declawing, owners’ perception of the outcome of declawing, and whether owners would be able to identify negative outcomes associated with declawing were opinions. Given what we have learned about the neurophysiology of mammals in the past 30 years, there should no longer be any debate about whether all mammals, including cats, feel pain. More recently, veterinarians have made substantial strides toward understanding how cats express both acute and chronic pain.² This information requires attention from all veterinarians evaluating declawed cats on a regular basis, no matter the reason for examination.

Dr. Neunzig is correct that “poor surgical technique is unacceptable regardless of the procedure performed,” but this statement needs clarification with regard to declawing as there does not appear to be a standard technique for declawing that is consistently used across the profession. For example, one study³ found that 63% of a population of declawed cats that underwent radiography had distal phalangeal fragments that had been left behind.

In addition, many questions regarding the long-term effects of declawing remain unanswered: What happens to the cartilage on the distal end of the middle phalanx? Could damage to the distal articular cartilage of the middle phalanx lead to subchondral sclerosis, as can be seen in humans?⁴ Why do some paw pads become misaligned with the middle phalanx? Does removal of the distal phalanges from the forelimbs alter weight distribution, leading to back pain, as can be seen in humans?⁵ Are neuromas common and how might they affect cats? What happens if the distal phalangeal growth plate is damaged? What happens if the digital extensor tendon is cut but not the deep digital flexor tendon?

Given these questions and concerns, I do not believe that the opposition to declawing is based on anthropomorphic concerns. Unfortunately, scientific literature detailing the long-term outcome of declawing in cats is not available. This may require us, as veterinarians, to extrapolate from human research, but doing so is not anthropomorphizing cats so much as applying mammalian anatomy and physiology across species. I believe that with continued attention to declawed cats, we will be forced to consider the possibility that we were in the wrong in perpetuating this procedure. Ultimately, veterinarians should be the leaders in advocating for the health of animals. Nontherapeutic, convenience-based declawing of cats does not provide any medical benefits to cats, has not been shown to prevent relinquishment of cats, and is not among the recommendations made by the CDC for the protection of immunocom-promised people.⁶ Therefore, it should not be available.

Nicole K. Martell-Moran, DVM, MPH

Feline Medical Center Houston, Tex

Preparing for practice

I can't thank Meindl et al¹ enough for their recent commentary “Never apologize for wanting to be ‘just’ a general practitioner.” This piece should be required reading for all first-year veterinary students, empowering them to resist the voices that will attempt to dissuade them from demanding an educational experience that truly prepares them for general practice.

As a general practitioner with more than 12 years in mostly mixed animal practice, I can attest that faculty advisors at my alma mater sometimes seemed more intent on preparing students for advanced study than on preparing me to hit the ground running after my four years. I was told that “the days of James Herriot are over.” As a nontraditional-age student, life had shown me that my rural hometown would welcome a caring, well-rounded, competent veterinarian able to work within budgetary limits. During my fourth-year clinic rotations, I often swam against the current by—unsuccessfully—requesting that I be permitted, with supervision, to do daily pressure bandage changes on my equine patient with colitis, pass a nasogastric tube on a horse with colic, perform pregnancy checks on cows and horses in various stages of pregnancy, and close skin incisions on selected surgery patients. I would, after all, be a living, working ambassador for my school. In my place, interns and residents practiced these hands-on skills over and over during my clinical year.

To their credit, I was taught by some very pragmatic clinical professors, and I am forever grateful for their unspoken recognition that the public will judge us by our results, not our pedigree. To me, other instructors seemed blind to the importance of imparting hands-on skills to students. For this reason, I recommend easing restrictions on fourth-year externship opportunities. Let students maximize their time in real-world practice settings. Institute a mandatory skills list for every student to master before graduation. They will be better prepared to enter general practice and thus less likely to feel the need to enter an internship because of lack of preparedness. Remember that students are the customers of the university system and that their feedback as both students and practitioners is critical.

Pamela J. Milligan, DVM

Chattahoochee Veterinary PC Cleveland, Ga