CHAPTER 5 Growth

Generalizations about normal growth in puppies and kittens are difficult to make; this is particularly true in respect to dogs because of the wide variety of breeds encompassing many body shapes and sizes. Dogs are one of the few species with such a variety of size, which makes metabolic and growth rates significantly different. Normal adult dogs can vary in size from less than 5 lb to 150 lb in weight and still be healthy. This diverse morphologic range is rarely seen in any other species. Not only are there differences in the length of the exponential growth phase but also in the individual rates of growth (Figure 5-1).

Figure 5-1 Mean growth curves for 11 breeds of dogs (SEM bars are excluded for clarity): English Mastiff (), St. Bernard (), Irish Wolfhound (), Great Dane (), Newfoundland (), Labrador Retriever (), Beagle (▪), English Springer Spaniel (), Cocker Spaniel (), Miniature Schnauzer (), and Papillon ().

(Adapted from Hawthorne AJ, Booles D, Nugent PA, et al: Body-weight changes during growth in puppies of different breeds, J Nutr 134:2027S-30S, 2004.)

Determination of appropriate growth for an individual animal can be difficult. Unless a particular animal is still with siblings or has an owner with a good understanding of not only this breed but also of this specific lineage, normal growth for a particular animal can be difficult to define. An example of this situation is manifest in the Dachshund—a breed in which miniatures (less than 11 lb) and standards (16 to 32 lb) can be whelped in the same litter. Generalizations about normal growth can be made between dog breeds that will attain approximately the same adult size (Table 5-1).

TABLE 5-1 Growth characteristics of different dog breeds calculated by fitting a logistics equation to growth curves^*

Many factors contribute to the normal development and growth of puppies and kittens. Genetics, environmental influences, endocrine and metabolic processes, nutrition, and disease are all major factors in determining growth. Growth is regulated by somatotropin (growth hormone), which triggers insulin-like growth factor-1 (IGF-1) release. When stimulated by thyroid hormone, IGF-1 is responsible for triggering cell proliferation, protein synthesis, and skeletal growth.

Growth of an animal is influenced by many factors, and it may be difficult to determine the specific contribution of each of the factors involved. These factors can include alterations in energy requirements as a result of the length of haircoat, breed temperament (compare the Jack Russell Terrier to the Clumber Spaniel), and body mass to surface area (English bulldog vs. the Whippet).

Assessment of normal stature in dogs can be difficult. Purebred breeds have written standards that include optimal size, usually height at the withers, but occasionally include weight guidelines (Table 5-2). Seasoned breeders usually have enough experience to recognize abnormal puppy growth trends. This does not mean all purebred dogs meet their standards requirement. Dogs with registration papers may or may not be “show” dogs; these “pet quality” dogs (graded as pet quality by the breeder because of a variety of faults, one of which may be size) are sold and should ideally be spayed or neutered. Unfortunately, the new pet owners may not sterilize their pets, and if the breed is particularly popular, may breed with another registered pet quality dog. Since these pet owners do not have the expertise in genetics or an understanding of the breed type, these puppies often have issues relative to their breed standards and frequently these dogs are much larger than the written standard requires. This is illustrated by the 100-lb registered Golden Retrievers (standard calls for 65- to 75-lb males) seen daily in the veterinary hospital.

TABLE 5-2 Desired heights and weights for dogs

Dogs that are bred, shown, and become champions have survived in the gene pool by meeting the rigors of independent judging in the show ring; by definition the dog show is designed to “exhibit” correct breeding stock. An example of this situation is the requirement for the Lakeland Terrier directed by its written parent club standard, which calls for the male to be inches at the withers ( inch). Another example are the Miniature Dachshunds, which are not to exceed 11 lb. Some standards require disqualification if size requirements are breached, whereas in other breeds, deviation from the suggested size (either height or weight) is considered a significant fault in the show ring. The net effect is that purebred dog breeds do have standard sizes that a veterinarian can obtain, which is useful in determining if a particular puppy is incorrectly sized (see Table 5-2). However, it should be remembered that a puppy may be considerably sized incorrectly and still be healthy. Mongrel puppies have no known expected growth guidelines, unless the veterinarian can get some information on the parents’ size. It must also be kept in mind that pregnancies that occur without human supervision may have multiple sires, thereby confounding the issue.

Breed-specific differences in growth patterns are affected by the dog’s ultimate adult size, temperament, and type of hair coat. Any condition that requires an increase in energy consumption can negatively affect growth rates if nutritional adjustments are not made. A Bulldog puppy may be more languid than Parson Russell or Wire Fox Terrier puppies, which have a much higher energy demand because of their increased activity levels. Breeds with longer, denser haircoats will require less energy to keep warm in cooler climates than shorthaired or thin-coated individuals. All of these types of influences will impact energy requirements, which will permit various growth rates either faster or slower when the animal is fed any diet with a fixed caloric density.

Exponential growth rates (log-body weight increased linearly) occur in all puppies, regardless of subsequent adult stature. This exponential growth rate continues until the puppy reaches approximately half its adult size. This period of tremendous rate of growth is prolonged with corresponding increases in adult size. English Mastiffs end this phase at about 23 weeks of age, whereas toy breeds have finished their exponential phase at 11 weeks of age. Interestingly, in one study, the fastest exponential growth rate occurred in English Springer Spaniels at 18%, whereas the slowest was in the English Mastiff at 10.8%. Growth rates, increase in percentage of body weight gain per week, are strikingly similar until half of adult size is reached. These early exponential percentage growth rates range from 13% per week in toy breeds to 17% per week in giant breeds.

The time necessary to achieve 99% of the adult body weight varies with the final adult size. Toys, small-, and medium-sized dogs achieve adult body size by 9 to 10 months of age. Giant breeds do not achieve 99% of their adult body size until 11 to 15 months of age.

There may be differences in growth rates of dogs of approximate equivalent adult size. This observance can be seen in differences between the Newfoundland, which had a lower adult body weight and a higher exponential growth rate than other giant breeds studied.

Male and female dogs have different growth patterns, with males taking longer to reach adult size. This may be a function of sex hormones affecting growth plate closure; however, the full etiology of the difference has yet to be fully elucidated.

Domestic cats, on the other hand, with a few exceptions, such as the large Maine Coon cat, are generally fit into the same size range relative to height. There are some substantial differences in size of skeletal structure and weight. Examples would be comparing many of the heavy-boned, stout English breeds with the slender athletic Southeast Asian breeds. The Cat Fanciers of America recognizes 39 breeds, each with a written standard. Only one has actual recommendations for ideal weight; the remaining recommendations are either generalized as small, medium, or large or do not address size at all (Table 5-3).

TABLE 5-3 Size recommendations for cats

Kittens grow on average 100 gm/week up to 6 months of age. Average-sized kittens weigh roughly a pound per month of age up to 10 months. When reviewing the feline growth chart, male kittens are usually in the upper two-thirds, whereas females routinely fall into the lower two-thirds (Figure 5-2).

Figure 5-2 Mean growth curves for domestic cats. This graph is a relative growth time line for kittens.

(Data from Harlan Sprague Dawley, Inc., July 1, 1996, catalog.)

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