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Protein in the Diet

By Lew Olson • November 2005 Newsletter
This month is covering the third session of the Nutrition Course. Protein is an important topic, as protein is needed for organ integrity, skin and coat, the immune system and energy. We will cover what foods contain protein, what protein consists of and what the protein needs are for dogs.

Most foods contain proteins, carbohydrates and fats. The foods most commonly thought of as containing proteins are meat, fish, eggs and dairy. Grains and vegetables also contain proteins, but not all proteins are equal.

Proteins are groups of amino acids in various chain lengths. These are usually linked in numbers of three to ten. The pancreas secretes digestive enzymes called protease (proteolytic enzymes), that break these down into smaller chains, which enable them to become ready to be absorbed by the small intestine. Except in a very few cases, intact proteins cannot be absorbed. However, puppies until 24-48 hours after birth are able to do this while ingesting colostrum, to allow them to gain temporary immunity.
There are two types of amino acids, essential, and non-essential. The non-essential amino acids can be supplied in the diet, or the dog’s body can synthesize them. The essential amino acids need to be present in the food that dogs consume to be available for them. These amino acids include:
Essential Amino Acids
*Taurine has been considered a non essential amino acid in dogs, but recent studies have indicated that it may likely be conditionally essential.
Nonessential Amino Acids
Animal proteins are considered complete proteins and plant proteins are called incomplete proteins. This refers to the amino acid profiles contained in these proteins.
Amino acids that are often missing in plant proteins include arginine, taurine, methionine, lysine and tryptophan. Corn does not contain any glycine, lysine or tryptophan. The lack of these essential amino acids denotes the protein quality of the food. Meat contains all the essential amino acids, and is considered very high quality. The measure for assessing the protein quality is based on the chicken egg, which is considered to have all the amino acids needed in sufficient amounts.
Protein Digestibility List
Egg whites: 1.00
Muscle meats (chicken, beef, lamb): 0.92
Organ meats (kidney, liver): 0.90
Milk, cheese: 0.89
Fish: 0.78
Rice: 0.72
Oats: 0.66
Wheat: 0.64
Corn: 0.54
Note: Values in this table are approximate, as they have been taken from several nutritional sources and personal communications with nutrition experts.)
Second to the quality of egg protein is animal protein (meat and organs) at about 90% digestibility, and the least quality is plant proteins, which fall as low as 45%. It takes more plant proteins than animal proteins to give the adequate protein percentages, and even at that, some amino acids will be lacking. It seems more sensible to feed meat protein, which is more protein dense, to achieve the amino acid profiles needed for dogs.
Heat is another factor in amino acid integrity. Studies have shown that high temperatures, or long time exposure to heat, can alter the amino acid chains. This can cause either a loss or a lowering of the quality of these proteins. (1) Meat cooked at extreme temperatures, over a long period of time loses more nutritional quality than meat cooked less than twenty minutes. While such cooking may be necessary for omnivores, carnivores have digestive tracts designed to readily and easily digest meat that is raw.
In a study Dr D.S. Kronfeld conducted in 1982, he concluded after analyzing the protein content of dry and canned dog foods, “Two reservations on this point concern the high fiber content of the canned product intended for older dogs and the possibility of over cooking the dry foods, for both of these factors tend to depress protein digestibility. Overcooking form amino-aldehydo bonds between protein and soluble carbohydrates, and this particularly interferes with availability of certain amino acids, notably lysine.”
Dr Kronfeld also reports that overcooking of dog foods destroys the amino acids methionine and histidine, and the cooking reacts with the proteins and starch to produce such side products as caramel, which contains no nutrients for a dog. As protein quality decreases, more is needed to meet the dog’s needs. However, if more poor quality proteins are added, the dog will still not get the amino acid requirements.
Poor quality proteins are more taxing on the liver and kidneys to process and digest. This can create a strain on these organs, which is even more difficult for a dog with compromised kidney or liver function. The added strain on an already diseased organ can further complicate these diseases.
Dr Kronfeld reports that older dogs and dogs with compromised kidneys can easily process high quality proteins. He states that high quality proteins in percentages as high as 54% can actually kill bacteria in the kidneys and create an acidic condition that is healthier for these organs. This would be helpful for urinary tract infections and other bacteria in the dogs system. (2)
Similarly, Dr Bovee’s research in the mid 1970’s concluded that high protein levels were more advantageous to dogs with deteriorating kidneys. He reported that the kidney function was much better in dogs fed a diet of 54% protein than 27% protein, for up to two years in his studies. (This study is in complete opposition to the recommendations of the NRC (National Research Council) for low protein for dogs with renal disease.) The same studies concluded that high percentages of protein in the dogs’ diet also help to kill bacteria in the urinary tract. (3)
Furthermore, a study was designed to test the hypothesis that restricting protein intake in older dogs may protect the kidneys and experimental dogs were divided into two groups. Dogs in both groups had a kidney removed to increase vulnerability of the remaining kidney to any protein effects. One group was fed a low protein diet (18%) and the other group received a higher protein diet (34%) for the subsequent four years. Results of this study indicated that there were no adverse effects from the higher protein diet, and mortality was actually higher in the lower protein group. (4)
A summary of eight studies done on dogs with reduced renal mass found that levels of protein up to 45% in the diet had no harmful effect on the kidneys. (5)
Another question is on protein and senior dogs. Many commercial foods now sell formulas designed specifically for the needs of the senior dog. These are often diets that offer lower protein, but studies show that this can cause more harm than good.
A diet rich in protein is especially important for older dogs. Senior dogs appear less efficient at metabolizing protein, so they require additional protein in their diets to help compensate. In fact, research has shown that healthy older dogs may need as much as 50 percent more protein than normal young healthy adult dogs. (6).
The importance of providing adequate dietary protein to senior dogs was brought out in research conducted at the Purina Pet Care Center. In this study, 26 English Pointers, ranging from 7 to 9 years old, were fed diets that were either 15 percent or 45 percent protein over several years. Dogs fed the high-protein diet maintained a directionally higher percent of lean body mass and lower percent of body fat (6).
There is also more information on protein needs in the newsletter
Protein, Kidneys & Seniors
The need for high quality protein is also applicable for puppies. Too little protein will do more harm than good, and there is no research to show that too much protein is damaging to a growing puppy.
“Dietary protein requirements are much higher for growing puppies than for fully grown dogs. In addition to supplying the protein needed to support protein turnover and normal cellular metabolism, protein is needed to build growing muscles and other tissues.” (7)
“Research at the Purina Pet Care Center and at other facilities has shown that puppies fed inadequate protein do not grow as well and are more susceptible to health problems than those fed nutritionally complete diets. At the Pet Care Center, English setter puppies that were fed a low-protein diet showed stunted growth compared to puppies fed higher levels of protein. However, when the protein level was increased in the puppies at the Pet Care Center, the deficiency was corrected.” (7)
“Concern about protein causing developmental bone problems in large-breed puppies has led some breeders to reduce the amount of protein they fed. However, in research published in 1993 based on studies of Great Dane puppies at Utrecht University in the Netherlands, it was shown that dietary protein does not contribute to these problems.” (7)
“Herman A. Hazewinkel, D.V.M., Ph.D., professor of veterinary medicine at Utrecht University, led the research that found no detrimental effects from protein levels up to 32 percent of the diet. However, puppies fed a diet of only 15 percent protein showed evidence of inadequate protein intake.” (7)
“Too low protein decreases the growth rate of puppies and also their immunological response,” Hazewinkel says. “This is true for large- and small-breed puppies. An adequate protein level should be higher than 15 percent.” (7)
“This study, conducted in young Great Danes during their first half-year of life, concluded that dietary protein increased to 32 percent does not negatively affect skeletal or cartilage development in these dogs. The research also confirmed that dietary protein did not have detrimental effects on liver and kidney functioning.” (7)
So the conclusion of the above referenced research stresses the need for high quality protein to achieve the best growth and immune systems. No proof was found that protein amounts affect skeletal growth adversely, except when using too little or too poor quality.
Since dogs are carnivores, and their digestive systems are designed to handle large amounts of raw meat and fat, it would seem logical that they would do better on a diet that nature intended. Cooking animal protein changes many amino acids chains, and makes some of the amino acids dogs need unusable. Dogs’ needs for amino acids differ from humans, and raw meat contains many or most ingredients for good tissue health, immunity and good coat and skin for carnivores.
For more information on this, see the article on Vegetarian Diets for Dogs
The bottom line is that protein is important for dogs in all stages, and the quality of the protein is equally important. This also lends to the need for variety in the diet, to insure that a wide spectrum of amino acids is being provided. This would include red meat, poultry, organ meat, dairy and eggs. No one choice will offer the variety needed for good health, and protein needs cannot be met by feeding grains, starches and vegetables. While these may lend fiber, some minerals and vitamins, only animal based proteins will give the full array of amino acids that is needed for canine good health and longevity.
In December we will be covering “Carbohydrates in the Diet”, so see you then!
(1) Kronfeld, DS PhD DSc MVSc, Protein Quality and Amino Acid Profiles of Commercial Dog Foods, (Journal of the American Hospital Association, July/August 1982, Vol. 18) 682-683
(2) Kronfeld, DS PhD DSc MVSc, Home Cooking for Dogs, Food Energy-Carbohydrates, Fats and Proteins, (American Kennel Club Gazette, June, 1978) 64
(3) Bovee, KC DVM, Dietary Considerations in Chronic Renal Failure, (Canine Nutrition, University of Pennsylvania, School of Veterinary Medicine, 1972) 37-38
(4) Finco DR, Brown SA, Crowell WA, Brown CA, Barsanti JA, Carey DP, Hirakawa DA. Effects of aging and dietary protein intake on uninephrectomized geriatric dogs. Am J Vet Res. 1994 Sep; 55(9):1282-90.
(5) Summary of Experiments on Dogs With Reduced Renal Mass That Examined Renal Effects of Diet.
(6) Ralston Research Fellow Dottie Laflamme, D.V.M., Ph.D. Nutritional Needs Of Older Dogs.
(7) Breeder’s Magazine
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