Nutrition

We hear about the minimum daily requirements (MDR) for nutrition all the time. Whether for us or our pets, food labels trumpet that they meet the MDR for protein, carbohydrates, vitamins, minerals and the list goes on. We all know that these are established amounts of different aspects of nutrition that someone, somewhere determined that humans and animals need in order for our bodies to carryout their basic functions.

But how are MDR’s established? If there’s a minimum, what’s the maximum? Who decides? There are many websites and articles premised on the idea that MDR’s are fabricated or so low that cardboard sprayed with vitamins would meet the requirements. Although the in-depth investigation of animal nutrition is still new and evolving, the knowledge grows greater every year with studies by academia, industry and regulatory agencies.

First, the who; in the U.S., the Nutrition Resource Council, part of the National Academies of Science (NAS), are the busy bees who determine the levels of nutrition for humans and domesticated animals. It is their findings that the Department of Agriculture and (for the most part) the Food and Drug Administration base their requirements the food industry to follow. The NAS has their own research laboratories, but also gathers information from studies done by universities and the food industry. The NAS Board on Agriculture is the department setting the requirements for domesticated animals.

Next, the science; dry and boring as it is, it’s really important. Nutrition amounts are based on how much energy is produced by a food. So, a food is placed in a bomb calorimeter (I can only imagine what one of those looks like!) and completely oxidized (broken down). The total combustible energy released is known as gross energy. But not all gross energy is available for metabolism, these is some loss in feces, gas and urine (now, that’s gross energy!). So subtract for waste and you have metabolizing energy (ME) in various proteins, fats and carbohydrates – the basic building blocks in which all mammals break their food down.

Determining energy requirements for all dogs is not a simple task as adult size and growth rates of breeds vary greatly. For testing purposes, dog breeds are divided into small, medium and large, using an average age of 6 years, and an average body weight, the NRC uses an equation to find the relationship between basal metabolic rate (BMR) and metabolic body weight (MBW) and this is used to establish how much ME dog’s of each size need. From this, they determine how much protein, fat and carbohydrates are needed to fulfill an average dog of a certain size’s MDR. How’s that for a lot of initials?!

Next, purebred dogs of various sizes and ages are fed controlled, purified diets for 60 weeks. Regular blood and fecal tests are done to determine what nutrients, vitamins and minerals the dogs have present in their blood and waste. Physical exams including stress tests are also performed to see if the dogs are healthy, with appropriate growth for pups. Through this, the types of nutrients and some vitamins are determined.

Problems with the studies: Most studies have been in controlled environments. Recent studies, however, have shown that temperature, shelter or the lack of it, amount of exercise and even hair growth affected energy requirements. Next, different breeds have hereditary issues that may affect the ability to convert food into energy. Mixed breeds may have a combination of hereditary factors affecting nutritional requirements.

Vitamins and Mineral: Here’s where it gets murky (murkier) – the NRC states: “Certain vitamins have been recognized as essential nutrients for dogs for more than 60 years. Despite this long history, precise quantitative requirements have not been established for every vitamin.” Vitamins that have been studied include A, D, E, K, Thiamin, Riboflavin, Pantothenic Acid, Niacin, B6, Biotin, B12, Choline, and Vitamin C (dogs synthesize this themselves and don’t need to get it from food). Minerals are in the same boat and the NRC points out, “It is common practice to include all the minerals shown to be required by other mammals in the formulation of dog diets, even though the quantitative requirements for all minerals have not been established experimentally for this species. (emphasis added)”) Vitamin and mineral concentrations are based on 1) estimates from the requirements of other species; 2) from data obtained from studies that involve dogs even though they weren’t designed to study nutrient requirements, but still had results that yielded nutritional information; 3) from experience with diets that resulted in acceptable performances in dogs.

Other guidelines from the NRC: puppies require about 2 times as much energy per unit of body weight as adult dogs of the same breed and should be given multiple daily meals. You should decrease the amount to 1.6 times (approximately) when 40% of adult body weight is achieved and 1.2 times when 80% of adult weight is reached. Too much food given from weaning to adolescence can result in maximal growth rates and cause improper skeletal development. A little too lean is always better than overweight, especially in puppies.

Pregnant bitches need only slightly more food than those recommended for non-pregnant dogs for the first two-thirds of gestation. During the last two weeks, energy requirements may increase to as much as 150 to 160 percent of preconception values. Energy requirements during lactation increase greatly and are influenced by size of the litter. Bitches with large litters may require 3 or more times their normal energy requirement. The ability to meet these requirements may be limited by the capacity of the bitch to consume sufficient food (think picky eaters). Foods of high nutrient density (more protein, fat and carbohydrates) are recommended for feeding at this time.

Working dogs require more food, but again, a leaner dog is a healthier dog. Also, dogs living in hot, humid conditions may need more food, especially if they are working or involved in performance events and training.

Ironically, the bottom line from the NRC: “Regardless of the accuracy of any prediction of energy requirements, the judgment of how much to feed is ultimately with the individual feeding the dog. This judgment is based on weight, conformation, and general appearance of the dog in question.” After all experts, the studies and the mathematics, it’s still up to us to determine how much to feed our dog!

The bottom line? Nutritional research is still a new and evolving science. It changes daily for humans where there are many studies ongoing. Nutritional analysis for animals lags far behind that of humans. So, expect the data to change and new discoveries to be made yearly. Try to stay up on the latest information through websites and newsletters. Your Vibrant Pets® website, the National Resource Council, Association of American Feed Control Officials, Center for Veterinary Medicine and the USDA all has both online and hard copy resources available to the general public.