Page 92 - Small Animal Clinical Nutrition 5th Edition

92 Small Animal Clinical Nutrition

size each protein must be present. The amino acid in shortest
Table 5-16. Ideal amino acid profiles (relative to lysine) for supply relative to demand is called the “first limiting amino
dogs and cats.*
VetBooks.ir Amino acids Dogs Cats acid.” An imbalance occurs when one or more amino acids
Lysine
needed, but at least one other amino acid is provided in excess
0.64
1.00
Methionine + cystine 1.00 1.00 needed for protein synthesis are not available in the quantity
Tryptophan 0.22 0.19 (Harper et al, 1970). Amino acid antagonism occurs when
Threonine 0.67 0.87
Arginine 0.71 1.12 amino acids have similar chemical structures (Harper et al,
Isoleucine 0.57 0.63 1970).Typically, an excess of one of these amino acids increas-
Valine 0.75 0.75 es the requirement of one or more chemically similar amino
Leucine 1.00 1.50
Histidine 0.29 0.38 acids (antagonism). Amino acid imbalance or antagonism
Phenylalanine + tyrosine 1.00 1.12 does not typically occur in animals consuming commercial pet
*Baker DH, Czarnecki-Maulden GL. Comparative nutrition of cats foods because most foods use complementary proteins (plant
and dogs. Annual Review of Nutrition 1991; 11: 239-263.
and animal sources). However, even use of complementary
protein sources can result in imbalances or deficiencies of
other amino acids. Therefore, it becomes important to under-
food than low-calorie foods. The opposite is also true. Larger stand the optimal levels and ratios of the essential amino acids
portions of low-calorie foods are typically consumed; therefore, necessary for animals.
animals can adequately meet their daily requirements with a The ideal or perfect protein concept was first established in
food that has a lower percentage of protein. swine. This concept defines the ideal ratio of essential amino
Adult animals also need dietary protein to replace the amino acids necessary to maximize tissue growth and diet usage.
acids that enter pathways of amino acid catabolism and are Researchers used the same concept for dogs and cats by extrap-
permanently lost. Healthy adults also have a daily requirement olating data from requirement studies using foods with purified
for protein to replace nitrogen lost as urea, ammonia, creati- amino acids (Baker and Czarnecki-Maulden, 1991). The
nine, nitrate in urine and feces, sloughing of epithelial cells in requirement of each amino acid was determined by feeding
skin and the GI tract, sweat, hair, nasal secretions, semen from graded levels of essential amino acids (with the same metabo-
males and secretions due to reproductive cycles in females. lizable energy) to puppies and kittens. These amino acids were
Dietary protein that must be consumed each day to replace the then compared to the lysine requirement. Thus, the ideal pro-
obligatory nitrogen loss is termed the maintenance protein tein concept creates ratios of the essential amino acids to lysine
requirement. and is independent of total dietary nitrogen (crude protein of
Adult and growing animals have maintenance requirements the food) and energy levels (Table 5-16). This ratio assures the
for protein, but only growing animals have the additional pro- protein in the food is “perfect” by containing optimal levels of
tein requirement for growth. The additional protein required amino acids (no imbalances or deficiencies).
by pregnant and lactating animals really supports growth. An
animal’s physiologic state also may result in increased or Protein Requirements for Dogs and Cats
decreased protein catabolism and nitrogen losses. For exam- The absolute minimum dietary protein requirement can be
ple, patients with cancer, burns and trauma may have estimated by feeding extremely high-quality protein or com-
increased daily protein requirements. monly used protein sources. If the estimate is based on feed-
Nitrogen balance is the difference between the nitrogen ing high-quality protein (e.g., lactalbumin), a growing dog
consumed and the amount lost each day. Growing animals, requires approximately 18% DM protein and an adult dog
pregnant females and any animals that are replenishing or about 8% DM protein (NRC, 2003). AAFCO has estab-
rebuilding tissue are in positive nitrogen balance. Zero nitro- lished that canine foods containing commonly used protein
gen balance occurs in normal healthy adults receiving mini- ingredients should contain at least 22% DM protein for
mally adequate or more than adequate dietary protein when growth, and 18% DM protein for adult maintenance (2007).
nitrogen output equals nitrogen intake. Negative nitrogen It is important to note that AAFCO recommendations
balance can occur during lactation, starvation or fasting when should be interpreted as daily allowances, not as absolute min-
there is inadequate or no protein intake. Excessive body pro- imum requirements.
tein catabolism due to burns, injury, fever, infections, hor- Growing kittens and adult cats have higher protein require-
monal imbalance or psychological causes can also cause neg- ments than most other domestic species. The minimum pro-
ative nitrogen balance. Amino acid imbalances and antago- tein requirement has been estimated to be about 18% DM for
nisms can cause negative nitrogen balance even when ade- kittens and 16% DM for adult cats, assuming use of extreme-
quate amounts of protein are consumed. ly high-quality protein sources (NRC, 2003). For commercial
foods using commonly available protein sources, AAFCO has
IMBALANCE AND ANTAGONISM recommended that foods for kittens and adult cats contain at
Essential amino acids must be provided in adequate least 30 and 26% DM protein, respectively (2007). Again,
amounts and in proper balance. When amino acids are used AAFCO recommendations for protein should be interpreted
for protein synthesis, all the amino acids necessary to synthe- as daily allowances, not as an absolute minimum requirement.