Page 95 - Small Animal Clinical Nutrition 5th Edition

Macronutrients 95

5-2). If specific essential amino acids are deficient, the clinical direct effects protein excess might have on the progression of
VetBooks.ir signs can be similar to those of general protein deficiency. A subclinical renal disease (Klahr, 1989), excess protein may con-
tribute to acidemia (Chapter 37).This development is especial-
deficiency of calories (energy) and essential amino acids (pro-
ly important in older cats with marginal renal function. Thus,
tein-energy malnutrition) increases catabolism of muscle and
other body proteins (e.g., albumin and immunoglobulins). even in apparently healthy dogs and cats, excess dietary protein
Continued failure to consume protein results in muscle atro- may at times be conditionally toxic.
phy and decreased blood levels of albumin, transferrin, thyrox- Protein excesses are found in pet foods for several reasons.
ine-binding protein and retinol-binding protein because car- Cats are strict carnivores (Chapter 19) and have a higher pro-
bon skeletons from these proteins are used as an energy source tein requirement than dogs, which are omnivores (Chapter
to supply glucose through gluconeogenesis. 12). However, some pet food companies have perpetuated the
Albumin concentrations in serum are not a particularly sen- myth that dogs are carnivores and that meat-based, high-pro-
sitive indicator of short-term protein malnutrition because the tein foods are more natural and thus better than lower protein
turnover rate is relatively long. Fatty liver can also be a sign of foods that contain both animal and plant sources of protein.
protein deficiency because specific apolipoproteins needed by Other fallacies, such as high levels of dietary protein build
VLDL to package and export fat from the liver are not synthe- more muscle or a thicker coat, have contributed to pet owners’
sized in adequate quantities or at all during protein deficiency. mistaken perception that higher protein is indicative of a high-
er quality pet food.
Protein Toxicity/Excess Excess protein adds unnecessary cost to foods. Excess protein
Although not a practical problem, amino acid toxicity can is used for energy. As an energy source, protein is no better than
occur if any amino acid is fed at a very high level. It is very digestible carbohydrate; however, protein is a more expensive
hard to create an amino acid toxicity by feeding protein energy source. The increased costs associated with increased
sources from plants or animals; however, synthetic amino dietary protein are invariably passed on to pet owners.
acids mistakenly added to foods at very high levels can cause There are no nutritional reasons that support providing
toxicity (Harper et al, 1970). Synthetic amino acids currently excessive amounts of dietary protein. After the protein/amino
added to some pet foods include L-methionine or D,L- acid requirements are met, additional protein provides no addi-
methionine, L-lysine, L-arginine and taurine. tional benefits. Thus, dog foods for adult maintenance should
The minimum dietary protein requirement for healthy adult not exceed 30% DM protein. Cat foods for adult maintenance
dogs is about 8% (DM) (NRC, 2003); however, AAFCO rec- should not exceed 45% DM protein.
ommends that dog foods contain a minimum of 18% DM pro-
tein (2007). Healthy adult cats require a minimum of 16% DM Sources
protein (NRC, 2003); however, AAFCO recommends that Many ingredients supply protein/amino acids to pet foods
foods contain at least 26% DM protein (2007). Commercial (Table 5-17). Typical pet food ingredients that have high-pro-
dog foods contain three to seven times the minimum protein tein concentrations are animal tissues from chicken, turkey, fish,
requirement. Some commercial cat foods contain two to four beef and lamb and viscera such as livers, lungs and spleens.
times the minimum protein requirement (Chapter 20). Grains also supply protein to pet foods. In fact, a large portion
Excess dietary protein can be problematic for dogs and cats of the protein in cereal-based dry pet foods typically comes
with specific disease conditions. For example, any disease that from grains, including rice, corn, wheat and barley. Some plant
affects organs involved with conversion of ammonia to urea and products (e.g., soybean meal and corn gluten meal) are concen-
waste nitrogen disposal can result in accumulation of toxic by- trated sources of plant protein.
products of protein metabolism. In particular, protein intake Multiple protein sources are often combined to improve the
above requirement should be carefully monitored in any animal overall quality and amino acid profile when foods are formu-
with impaired renal or liver function (Chapters 37 and 68). In lated. This method of improving protein quality is termed
other situations, such as struvite urolith dissolution in dogs and protein complementation (Zapsalis and Beck, 1985). Protein
adverse food reactions in cats and dogs, minimizing excess sources are combined based on their amino acid excesses and
dietary protein is a beneficial part of therapy (Chapters 31 and deficiencies so that the nutritional weaknesses of each source
43). In these cases, excess dietary protein could be considered will be counterbalanced by the strengths of other sources,
“conditionally toxic.” resulting in a food with high-quality protein. Corn and soy-
Feeding protein above requirements or recommendations for bean meal are typically used in animal food formulations to
healthy dogs and cats does not result in a true toxicity because take advantage of protein complementation. Corn protein is
the excess amino acids from the protein are catabolized and the low in lysine and tryptophan, whereas soybean meal is ade-
waste nitrogen is excreted. However, not all dogs and cats that quate in both amino acids. When used together in one food,
appear healthy are free of disease. Dogs and cats with chronic these two protein sources provide a well-balanced amino acid
renal disease are usually subclinical until the disease has pro- profile.
gressed to the point that two-thirds or more of functional renal Amino acid fortification is another method for improving
tissue is lost (Osborne and Stevens, 1981). Protein excess may the protein quality of foods (Zapsalis and Beck, 1985). Here,
contribute to progression of the disease. In addition to any one or more individual amino acids are added to a food when