Page 655 - Small Animal Clinical Nutrition 5th Edition

678 Small Animal Clinical Nutrition

ing puppies, are the effects of specific fatty acids on trainability
VetBooks.ir Box 33-3. Dietary Cation-Anion Balance. and the development of special senses. Studies indicate that
docosahexaneoic acid (DHA) is essential for normal neural,
Alteration of dietary cation-anion balance (DCAB) has been retinal and auditory development in puppies (Pawlosky et al,
1997). Similar results have been found in other species
reported to influence skeletal development in several species.
The DCAB of a food can be described, most simply, by the equa- (Pawlosky et al, 1997; Birch et al, 2002; Diau et al, 2003;
tion ([Na] + [K] – [Cl] mEq)/100 g dry matter (DM). As the DCAB Hoffman et al, 2003). The inclusion of fish oil as a source of
increases, the net physiologic effect is alkalinization. Conversely, DHA in puppy foods improved trainability (Kelley et al, 2004).
as it decreases an acidification effect is observed and calcium The conversion of short-chain polyunsaturated fatty acids to
excretion in urine is increased. Acidification will be buffered by DHA is an inefficient process in puppies (Bauer et al, 2005).
carbonate liberated from bone by increased osteoclasia, thus Thus, the essentiality of adding a source of DHA should be
increasing osteoporosis in adult and bone remodeling in young considered for this growth phase. The minimum recommend-
animals. The mechanism for these effects on skeletal develop- ed allowance for DHA plus eicosapentaenoic acid (EPA) is
ment is unclear. In addition, regulation of body acid-base bal- 0.05% (DM) with EPA not exceeding 60% of the total (NRC,
ance, calcium homeostasis and osmolality of the synovial fluid 2006). Thus, DHA needs to be at least 40% of the total DHA
compartment may be influenced. plus EPA, or 0.02% (DM).
The role of electrolyte balance in canine nutrition appears to
be most relevant to preventing canine hip dysplasia. Investigators
have associated the DCAB with the radiographic changes of sub- Calcium, Phosphorus and the Ca-P Ratio
luxation in the coxofemoral joints in several canine breeds.A food The amount of true calcium absorption in dogs ranges from 25
with a DCAB ([Na] + [K] – [Cl]) <23 mEq/100 g DM fed to large- to 90% depending on the amount of intake and the age of the
breed puppies was associated with less severe femoral head animal (Nap and Hazewinkel, 1994; Hazewinkel et al, 1991).
subluxation, on average, when the puppies reached six months Calcium is absorbed via three mechanisms: 1) active absorption,
of age.The slowed progression of subluxation was also observed 2) facilitated absorption and 3) passive diffusion. Passive diffu-
in dogs fed a food with a reduced DCAB from 33 to 45 weeks of sion is especially important in young animals. Active absorption
age. Hip joint laxity was determined using Norberg hip scores is most important in the proximal GI tract.Passive diffusion and
computed from radiographs. Significant correlation between facilitated absorption, however, are important in the distal GI
radiographic findings (e.g., Norberg hip scores) and progression tract, primarily because of prolonged transit time and increased
of canine hip dysplasia, either radiographic or clinical, was not
proved. The authors proposed the balance of anions and cations calcium concentration through that section. Vitamin D 3
3
in the food (specifically Na, K, Cl) influenced the electrolytes and metabolites, especially 1,25-dihydroxyvitamin D , are the most
osmolality in joint fluid. The joint fluid of dysplastic dogs has important hormonal regulators of GI calcium absorption (Birge
higher osmolality and is increased in volume when compared and Avioli, 1990). Analysis of 90 dogs revealed that active calci-
with that of disease-free hips from dogs of the same breed. The um absorption decreases with increasing age, whereas passive
changes in osmolality and fluid volume could be a result rather absorption remains constant during the period of rapid growth.
than a cause of canine hip dysplasia. These studies suggest an When calcium intake is high, active absorption becomes negli-
association between DCAB and joint laxity without proving a gible and passive absorption accounts for up to 53% of total
mechanism of action. Most commercial growth foods encompass absorption of the amount eaten.There is no difference between
a very small range of DCAB and probably do not vary greatly in breeds (Tryfonidou et al, 2002). Previous studies showed serious
risk. consequences for skeletal development in large-breed dogs
In commercial dog foods, the relation between cations and
anions is 22 to 46 mEq/100 g DM. The balance of only the elec- (Hazewinkel et al, 1985) but not for small breeds (Nap et al,
3
trolytes Na, K, Cl, calculated as equivalents, will be between 15 1991). PTH, vitamin D and dietary cation-anion balance
to 42 mEq/100 g DM. Feeding foods with a dietary anion gap of modulate renal handling of calcium (Box 33-3), whereas calci-
8 mEq/100 g DM lowered the severity of subluxation of the tonin does not play a significant role in this aspect in dogs.
femoral head in growing dogs of different breeds. Increasing this In the face of adequate levels of calcium in the food, the
relation to 41 mEq/100 g food was accompanied by a higher absolute level of calcium, rather than an imbalance in the calci-
degree of subluxation as determined by the Norberg angle on um-phosphorus ratio, influences skeletal development (Haze-
radiography. Because the knowledge and experimental databas- winkel et al, 1985; Hazewinkel et al, 1991) (Boxes 33-4 and 33-
es are very small in dogs, mineral salts should not be added in 5). In one study, the prevalence of DOD was significantly
large amounts to nutritionally balanced foods. Problems may increased in young, giant-breed dogs fed a food containing
arise not only from the addition of anions, but also from increas- excess DM calcium (3.3%) with either normal DM phospho-
ing the amounts of cations. Further research is needed in this
field but it seems prudent to avoid excessive acidifying foods or rus (0.9%) or high DM phosphorus (3%, to maintain a normal
acidifying agents in growing puppies. calcium-phosphorus ratio) (Hazewinkel et al, 1991). These
puppies apparently were unable to protect themselves against
The Bibliography for Box 33-3 can be found at the negative effects of long-term calcium excess (Hazewinkel et
www.markmorris.org. al, 1985; Tryfonidou et al, 2002). Furthermore, long-term cal-
cium intake increases the frequency and severity of osteochon-
drosis (Nap and Hazewinkel, 1994). The minimum calcium