Forty-odd years ago, growing up with a Great Dane, the only factor considered was the cost of the food. In the 1970s very little was known about canine nutritional requirements. In fact, it was 1991 before a paper citing nutritional requirements for different sizes of dogs was published (Burger and Johnson, 1991) and a further 6 years before the first commercially prepared large-breed diet was launched by Royal Canin®. Since then, nutritional knowledge has continually deepened, with thousands of publications available on PubMed for those who are interested.
By the time most puppies and kittens reach adulthood, they will have increased their birth weight by 40–50 times (Case et al, 2011). However, owing to the great variation in dogs’ sizes, from tiny Chihuahuas at around 2 kg to Irish Wolfhounds at about 70 kg bodyweight, canine growth periods vary significantly (Figure 1). Cats and small-breed dogs usually reach physical maturity at 9–12 months of age; large and giant breeds, not until they are 18–24 months old (Case et al, 2011). If one considers that an adult giant-breed dog may weigh the same as an adult human, who would take 18 years to reach maturity, this is a remarkably rapid growth period.
Puppies and kittens are born helpless at birth, unable to stand, hear or see, and totally dependent on their mother for the first few weeks of life (Burger, 1995). Consequently, this pre-weaning stage carries the highest mortality rate around 10–30% (Cave et al, 2002). One important contributing factor, along with maternal behaviour and the aptitude of the breeder, is the quality of the mother's diet during the last trimester of pregnancy. With very few antibodies (only around 10–20%) crossing the placenta (Case et al, 2011), puppies and kittens rely on the high quality, and adequate quantity, of colostrum provided in the first 24–48 hours after birth, to support healthy development and, more importantly, to provide passive immunity against some infectious diseases during the first 4 months of life (Case et al, 2011). Colostrum is also important for the provision of other bioactive factors such as lysozyme, which prevents the growth of certain types of bacteria and bile salt-activated lipase, which aids in the digestion of fat (Case et al, 2011). If colostrum is unavailable (for example, as a result of the death of the queen), it has been shown that it may be beneficial to give serum from an adult cat by subcutaneous or intraperitoneal injection, to supplement the immunoglobulins not received via colostrum (Levy et al, 2001).
Growth of puppies and kittens
Both puppies and kittens are born with a low percentage of body fat, and so require a high-fat diet to increase body fat to around 22% by adulthood (Case et al, 2011). The polyunsaturated omega 3 fatty acid, decosahexaenoic acid (DHA), is considered essential for normal neurological and retinal development. Although puppies can convert eicosapentaenoic acid (EPA) or alpha-linolenic acid to DHA, this is an inefficient way to acquire it (Case et al, 2011). Studies show that retinal function and learning ability were better among 12-week old puppies who received preformed DHA as fetuses and during weaning, than those that did not. Therefore, the recommendation for both puppies and kittens is to receive preformed DHA during fetal and neonatal growth (Case et al, 2011).
The growth period can be broken into three stages:
During the pre-weaning stage, the bitch or queen will ideally provide all the nutrients required via her milk, unless she is unable to do so for any reason. At weaning, around 3–4 weeks of age, the animal is still growing rapidly and will need an energy-dense moist diet, which is easier to eat (as the teeth are still erupting) and should be highly digestible to avoid digestive upsets (Debraekeleer et al, 2010). In both species, weaning should be complete by about 6 weeks of age (Figure 2).
Post-weaning sees the most rapid growth phase until the animal reaches adulthood, although as mentioned, in dogs it varies with different breed sizes. Male kittens grow faster than females, with a daily gain of almost twice that of females, and their growth phase is longer (Malandain et al, 2006).
During growth, the need for energy is greater than at any other stage of a dog or cat's life, with the exception of lactation (Case et al, 2011). The growth phase can be broken into the following two stages:
Energy requirements
Energy requirements for growing puppies were defined by Burger (1995). Table 1 shows the huge increase in energy requirements for growing puppies; it shows clearly that an ideal growth diet should be very energy-dense and provided over several meals because of the sheer volume of food an animal may need to consume to fulfil daily nutritional requirements. The digestive anatomy of different-sized breeds should also be borne in mind. With a large-breed canine gastrointestinal (GI) tract being around 2.7% of its bodyweight (Grandjean, 2006), and a growing animal's GI tract being immature (Case et al, 2011), one could suppose that feeding energy-dense food is less likely to result in diarrhoea and reduced nutrient absorption. Of course, during the post-weaning phase, puppies and kittens are very active and curious, and a high-energy content helps facilitate this.
| Bodyweight | Age in months | ||||
|---|---|---|---|---|---|
| Kg | 2 | 3 | 5/6 | 12 | 24 |
| 1 | 1045 | 836 | 523 | 523 | 523 |
| 2 | 1756 | 1404 | 1053 | 878 | 878 |
| 5 | 4368 | 3494 | 2098 | 1747 | 1747 |
| 10 | 7348 | 7348 | 3528 | 2940 | 2940 |
| 15 | 9961 | 5977 | 3983 | 3983 | |
| 20 | 12 519 | 7411 | 4941 | 4941 | |
| 30 | 11 721 | 8373 | 6696 | ||
| 50 | 19 646 | 12 281 | 9823 | ||
| 60 | 14 082 | 11 265 | |||
During their first few weeks, puppies and kittens require very high-fat, high-protein milk. Table 2 shows the differences in milk composition between species. This illustrates why it is inappropriate to feed cow's milk if hand-rearing a puppy or kitten, as the levels of all nutrients in cow's milk are insufficient to fulfil the nutritional needs of puppies and kittens. The immune system is still developing and a number of studies have shown that supplementing with antioxidants, specifically with lutein, vitamin A and E and betacarotene, may help boost the immune response of puppies and kittens to vaccination (Kim et al, 2000; Koelsch and Smith, 2001; Khoo et al, 2005).
Post-weaning, but during the remaining growth phase, the diet should remain of high-energy density, with high digestibility, and adhere to guidelines from the European Pet Food Industry Federation (FEDIAF). If a diet too high in energy is fed, the growth rate will be accelerated (and conversely, with too little energy, growth rate will be retarded). However, there is no benefit to speeding up the growing process and, in the case of largeand giant-breed dogs, this can actually be detrimental to their health (Larsen, 2010).
One study showed that giant-breed puppies, who were fed ad libitum a high-energy food, displayed a multitude of skeletal abnormalities (Hedhammer et al, 1974). These included enlargement of the costochondral junctions and the epiphyseal-metaphyseal regions of the long bones; carpal flexor deformities (Figure 3); and sinking of the forelimbs — all of which resulted in pain and lameness.
In later studies, excess energy and the resultant rapid growth were found to contribute to canine hip dysplasia (CHD) (Case et al, 2011). Feeding a reduced-energy diet, which slowed down growth, showed a positive influence on joint formation, and the incidence of subsequent CHD and osteoarthritis was reduced (Kealy et al, 1992).
Key nutrients
Two key nutrients for consideration during growth are calcium and phosphorus. These should be present at optimal levels, remain in a ratio of approximately 1:1, and not be over-supplemented (FEDIAF, 2012). Recommended amounts, according to FEDIAF, are shown in Table 3. Dietary calcium and phosphorus supplements should never be added to a complete balanced diet for either cats or dogs. Owing to the immaturity of the intestinal wall in young animals, calcium absorption is passive during this phase and therefore unregulated (Case et al, 2011).
| Canine | Adult | Growth | Early growth(<14 weeks) | Late growth (>14 weeks) |
|---|---|---|---|---|
| Ca | 1.25 | 2.50 | 2.00 | |
| P | 1.00 | 2.25 | 1.75 | |
| Feline | ||||
| Ca | 1.48 | 2.50 | ||
| P | 1.25 | 2.10 | ||
Another complication of over-supplementation of calcium is hypercalcaemia and hypophosphataemia (Case et al, 2011), which lead to calcium deposits in the kidneys and, in turn, cause chronic renal failure and serious effects on the GI tract, cardiac function, and possibly neurologically (Gardbaum, 2013).
Hypercalcitoninism is another condition that was shown by Stephens et al (1985) to occur in dogs fed excess calcium during growth, resulting in a slowing of articular cartilage formation, and the possibility of eventual detachment of that cartilage, as seen in osteochondrosis including ununited anconeal process (UAP) (Figure 4). As the puppy or kitten approaches adult weight and growth slows down, there is a shift in energy use from growth towards daily maintenance requirements.
Copper and zinc are also important to consider during the growth phase. Copper is vital for osteoblast activity during skeletal growth and to absorb and transport iron, among other things (Case et al, 2011), and zinc is important for protein synthesis.
Protein requirements are higher in growth than in adulthood because of muscle-building in addition to normal maintenance needs. A summary of protein, energy and calcium effects on skeletal development and nutritional recommendations for large and giant breeds, who are the most sensitive to abnormalities during the growth period, can be seen in Table 4 (Case et al, 2011).
| Nutrient | Low | Medium | High | Nutritional recommendation | |
|---|---|---|---|---|---|
| Protein | Decreased growth rate if deficientd | Normal growth rate | Normal growth rate | 26–28% | |
| Energy | Decreased growth rate if deficient | Normal growth rate | Increased growth rate and risk of skeletal disease | 360–400 kcal/cup | |
| Calcium | Decreased growth rate. Decreased bone mineral content and strength | Increased bone mineral content and strength; proper conformation; reduced risk of hypertrophic osteodystrophy (HOD) | Increased bone mineral content and strength. Poor conformation. Increased risk of HOD | 0.8–0.9% Ca:P ratio = 1.2:1 |
There are many published studies showing that undersupplementation of calcium or over-supplementation of phosphorus can cause nutritional secondary hyperparathyroidism, usually because affected animals were fed a meat-only diet (Kawaguchi et al, 1993; Taylor et al, 2009; Krook and Whalen, 2010). Interestingly, a case of nutritional secondary hyperparathyroidism was even identified in a 3-month-old tiger cub (Won et al, 2004), having been fed a meat-only diet. This indicates that even growing wild cats can suffer without proper calcium: phosphorus ratios and levels.
Finally, it is vitally important that the ideal body condition score (BCS) of a growing puppy or kitten is maintained right from the start. This could be the key to reducing the risk of obesity later in life, as noted by Glickman et al (1995), who found that overweight adolescent dogs were more likely to gain excess weight as adults. A study of 41 growing, intact kittens in Zurich found that as early as 3–8 months, those with a higher-than-ideal BCS were already showing insulin sensitivity (Haring et al, 2013). Recent studies in rats have also supported this finding (Gwóźdź et al, 2016).
Conclusion
Growth dramatically affects the nutritional requirements of both cats and dogs if the adult animals are to be of optimal size, form and health. The growth periods of both species are fast and dynamic, and certain specific nutrients are essential for the correct formation of musculature, organs, the skeleton and various functions, including vision and brain development. In addition, for both species, maintaining an ideal bodyweight right from the start is a vital consideration for optimal, long-term health. Finally, inappropriate feeding during growth can lead to catastrophic skeletal abnormalities, particularly for large- and giant-breed dogs.