Reproductive patterns in the domesticdog : a retrospective study with theDrever breed as model

Abstract: Despite the long history of joint life between man and the dog (Canis familiaris), there are still many aspects of canine reproduction that are not well understood. Domestication of the dog from its ancestor the wolf is thought to have occurred at least 14 000 years agoIt is a unique situation that both the ancestor – the wolf, and the domesticated descendant - the dog, are still present world wide, which gives them a very important place in the fields of interest for scientific research. The reproductive pattern of the dog, as a very divergingspecies among all the mammals, requires specific methodology in research and studies.To study the differences between seasons of the year regarding the distribution of matings and whelpings, litter size, neonatal deaths and sex ratio, and the effects of age and parity of the bitch at the time of whelping on litter size, as well as the influence of litter size on thelength of gestation, and fertility and frequency of whelping problems in the domestic dog, data from the Swedish Kennel Club (SKK) registry for the Drever breed during 1995-2006, 2717 registered litters, was analyzed together with more detailed data from a private,professional kennel of Drevers, with 285 matings and 224 whelpings during the same time period. Significantly more matings took place during winter, and the fewest during summer. Most whelpings took place during the winter and spring seasons. Of the 224 pregnant bitches 78% whelped, 6.25% experienced dystocia, and 5.36% underwent a Ceasariansection. Duration of pregnancy was not different between seasons. The largest litters were born during spring. Litter size was significantly, negatively, correlated with the duration of pregnancy (r = -0.18). Each extra pup caused a shortening of the gestation by 0.25 days.Bitches giving birth to their first litter after 5 years of age produced a smaller litter than younger bitches. For all the whelpings, bitches gave birth to 0.33 pups less per litter per additional year of age. Litter size in the private kennel increased from the 1st to the 3rdparity, and then decreased. The number of registered pups, increased from the 1st to the 2nd parity in the SKK data and from the 2nd to the 3rd parity in the private kennel, and then decreased. Mating a bitch only once resulted in a smaller litter size compared to multiple matings. None of the studied factors had any influence on the sex ratio. There were significant differences between males in whelping rate among the mated bitches, but nodifference in mean litter size, which indicates a female problem rather than a male one. Available data strongly suggest that the domestic dog still is under a considerable seasonal influence, modified by ambient and management factors.