Nutritional considerations for optimal puppy growth-
Calcium and phosphate
Calcium is involved in many body functions, including coagulation, enzyme activation, regulation of endocrine hormone secretions, cardiac function, and control of neuro-muscular excitability. More than 99% of the body’s calcium is found in bone, in the form of hydroxyapatite and calcium carbonate within a protein matrix. This mineral structure contributes to the integrity of the skeleton in its supporting role. Both calcium deficiency and excess, in conjunction with the calcium: phosphate ratio, can lead to bone disorders during growth.
A deficiency of calcium in the diet results in nutritional secondary hyperparathyroidism and calcium cation when dogs are fed meat-only diets that are high in phosphate and low in total calcium concentration; one study reported that diets containing insufficient levels of calcium can lead to spontaneous fractures in growing great Danes fed ad lib (10).
Excessive calcium intake has been shown to inhibit bone and joint remodeling during growth, thus preventing normal bone and joint formation (8, 11). In great Dane puppies, researchers have demonstrated that a concentration of calcium as 3.3% dry matter (DM) basis was associated with an increased prevalence of radius curvus syndrome, osteochondrosis (OCD), retained cartilage core and stunted growth when compared to a diet containing 1.1% calcium (11). These osteochondrodystrophy lesions appeared at major load-bearing sites such as the proximal and distal ends of the humerus, radius, ulna and tibia, and also in sites where weight has no influence, such as in the ribs.
Small and large growing dogs are not comparable in terms of calcium tolerance. One report showed that in the miniature poodle, calcium concentrations that varied between 0.33% and 3.3%/kg DM provided apparently normal bone growth when compared to control dogs receiving 1.1% calcium (12). Nevertheless, a food with a high calcium concentration led to histological lesions in growing dogs of small breeds (from 2-6 months), but without any clinical signs of osteochondrosis (12). Collectively, these studies have shown that large and giant breed puppies have special requirements compared to small breed puppies.
Young puppies absorb calcium both passively and actively in their intestines. They are incapable of effectively protecting themselves against excess dietary calcium since at least 45-50% of intestinal calcium is absorbed regardless of the quantity ingested (10). Diets rich in calcium therefore lead to chronic excessive absorption of this mineral in the puppy. This excess calcium then stimulates the production of calcitonin, which decreases the blood calcium concentration in order to re-establish normo-calcemia. It is through this hormone that calcium produces its adverse effects for growth. The role of calcitonin is in fact to favor the deposition of calcium in the bone tissue and to slow resorption of calcium from the bone. However, in the growing period, the bone tissue is continuously turning over, so that there are considerable exchanges of calcium between bone and blood. These exchanges are slowed by the action of calcitonin, which results in inhibition of bone tissue remodeling, leading to abnormal bone structure and to osteoarticular deformations.
Vitamins and minerals
Although dietary requirements of trace elements and vitamins are higher during growth, there is no need to supplement commercial puppy diets with these nutrients. Moreover, some trace elements and vitamins including vitamin A, vitamin D and iodine may be toxic if supplemented excessively. In addition, supplementation with some trace elements (e.g. zinc) may interfere with the absorption of others - such as copper - and thereby induce secondary deficiencies.
A number of anecdotal accounts, mostly poorly regulated or uncontrolled clinical studies, have suggested supplementation with vitamin C could help in the prevention and treatment of hip dysplasia, osteochondrosis and panosteitis (13). However, there is no adequate scientific evidence to recommend routine vitamin C supplementation to prevent skeletal problems in growing dogs (1). It is well established that the dog is capable of synthesizing all the vitamin C that it needs in its liver. Moreover, large doses of vitamin C (1200 mg per puppy daily) have been shown to aggravate orthopedic problems in Labrador puppies (7,14). These observations show that vitamin C has no beneficial effect on the skeleton of puppies and excessive supplementation is contraindicated.
The puppy’s gastrointestinal tract undergoes a period of intensive growth starting in the very first hours after birth and continuing well beyond weaning. Lactase and enterokinase are especially active during the suckling period, whereas the activity of trypsin, chymotrypsin, and aminopeptidase progressively increases throughout growth (Figure 1). The activity of enzymes such as pancreatic amylase, some peptidases, maltase, sucrase and trehalase only increases after weaning. All of these enzyme changes have profound repercussions on the digestion of carbohydrates and proteins.
Puppies also have shorter gastric evacuation times and higher intestinal permeability than adult dogs (15,16). Size also has a significant influence on gastrointestinal function and should be considered in the selection of an appropriate diet for growth. Several studies have reported that when fed the same diet, large-breed dogs have a lower digestive tolerance than small-breed dogs (15-20).
These differences appear to be linked to anatomical differences: the gastrointestinal tract of a giant breed dog is proportionally smaller (2.8% bodyweight) than that of a small breed dog (7% bodyweight) (21), whereas the volume of the colon is 40 times larger (22). Studies comparing the digestive function of dogs of various sizes (miniature poodles, standard schnauzers, giant schnauzers and great Danes) showed that the overall ability to digest nutrients, the absorptive capacity of the small intestine, gastric emptying, and intestinal transit did not differ between dogs (15,16,18-20). However, a low overall absorption of electrolytes (possibly due to the increased permeability of the small intestine) and strong fermentative activity (from a particularly long colon transit time) are two significant differences that may explain the low quality of stools in large breeds.
Stress can also be a factor in explaining poor stool quality, especially in breeds of dogs in a constant state of alertness e.g. the German shepherd or hyper-active/highly energetic breeds such as the boxer, greyhound etc. Growth is also a period of learning and immense exploration. Collectively, all these challenges, and the physiological changes seen in the developing gastrointestinal system, may explain the higher likelihood for puppies to have soft stools and episodes of diarrhea (Figure 2). Therefore it is important that diets for puppies are not only designed to optimize growth, but also to facilitate optimal digestion and support of the gastrointestinal system.
Throughout growth, a puppy gradually loses the protective immunity received via the dam’s colostrum. During this time it also develops its own immune defenses from contact with the environment and (especially) from appropriate and timely vaccination. However within this period a window of vulnerability exists where the puppy’s own immune system has not yet developed adequate protection but levels of maternal antibodies have declined below protection thresholds (Figure 3). For optimal health this period of vulnerability needs to be minimized. Studies have clearly shown that supplementing the diet with a synergistic combination of antioxidants (vitamin C, vitamin E, taurine, lutein) can significantly increase the levels of serum antibodies, and protective levels are attained more rapidly following vaccination (Figure 4) (23). This illustrates a role for antioxidants in optimizing the response to vaccination and protection from life-threatening preventable infectious diseases, and therefore puppies should receive a growth diet supplemented with antioxidants.
Growth is a challenging and constantly changing period for the puppy and the nutritional needs differ based on the individual’s age, sex, size and breed. Providing a complete and balanced diet that is specifically designed to support a puppy’s unique needs is critical for optimal growth and prevention of disorders associated with growth. The key to successful growth is to monitor food intake and constantly adjust the amount fed to maintain ideal body condition.
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