Showsight May 2021



H istory and experience have demonstrated that when two or more breeders gather together, their conversation, oftentimes, centers on the number of pups born and what might have gone wrong. For years, breeders have speculated as to why some litters are larger than others. Since most breeders do not review the literature and are not trained in biology or in veterinary medicine, a review of these questions was addressed. BACKGROUND A review of how nature has addressed these topics shows us that animals adapt to their living conditions. For example, horses and cattle live in herds as herbivores and cover considerable distances each day. They tend to have a long period of gestation and pro- duce a single offspring. Their young are born among the herd as it moves slowly, because only in the middle of the great herd can they be protected. The problem is quite different for canines. They live in small communities and their young are born in a safe hideout. Because they hunt, they cannot afford a long period of gestation. The reason that carnivores usually do not have single offspring lit- ters stems from the nature of their existence. They must be con- stantly hunting to struggle for existence, and the casualties among their young are high. Severzov calculated that the morality among young wolves was 45 percent at the end of the first year, and a fur- ther 32 percent by the end of their second year, with a total loss of about 77 percent for all young wolves. If their litters consisted of only a few pups, the likelihood would diminish that the survivors could contribute to maintaining the survival of the species.

There are several ways to approach the study of litter size in dogs. One perspective is to look at what can influence the size of a litter; another is to study one-puppy litters. Goldbecker and Hart reported experiences with both. For the one-puppy litters, they suggested the use of foster mothers and treating the singleton as an orphan because they have similar problems. They believed that these pups needed siblings (or other dogs to interact with) in order to learn the rules of the dog world. To that end, it is generally accepted that, at least for canines, littermates provide valuable and necessary practice sessions. Interactions provide opportunities for using their teeth, developing eye contact, and a wide range of other canine behaviors that become useful as adults. Most of the small breeds, notably the Toys and Terriers, usually produce very small litters. This is, in part, because of their very small size, which limits their capacity to carry large litters. But in the larger breeds there are wide variations in litter size, ranging from 1 to 21 and, in some instances, they have been larger. Breed- ers have, for years, unsuccessfully tried to make improvements in litter size via breeding and selection techniques—with little suc- cess. While many traits have high heritability, litter size is not one of them. It has a low heritability (around 10-15 percent), which means that one cannot count on the genes to increase the number of pups born. What can be expected will largely be determined by the non-additive factors of dominance. For example, wither height has a heritability estimate of 40-65 percent, which is reasonably high. Therefore, it is relatively easy for the breeders of the German Shepherd Dog to produce offspring with high withers. However, when it comes to litter size, selecting parents that come from large


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