The effect of inbreeding, body size and morphology on health in dog breeds

Abstract

Background: Dog breeds are known for their distinctive body shape, size, coat color, head type and behaviors, features that are relatively similar across members of a breed. Unfortunately, dog breeds are also characterized by distinct predispositions to disease. We explored the relationships between inbreeding, morphology and health using genotype based inbreeding estimates, body weight and insurance data for morbidity.

Results: The average inbreeding based on genotype across 227 breeds was F_adj = 0.249 (95% CI 0.235-0.263). There were significant differences in morbidity between breeds with low and high inbreeding (H = 16.49, P = 0.0004). There was also a significant difference in morbidity between brachycephalic breeds and non-brachycephalic breeds (P = 0.0048) and between functionally distinct groups of breeds (H = 14.95 P < 0.0001). Morbidity was modeled using robust regression analysis and both body weight (P < 0.0001) and inbreeding (P = 0.013) were significant (r² = 0.77). Smaller less inbred breeds were healthier than larger more inbred breeds.

Conclusions: In this study, body size and inbreeding along with deleterious morphologies contributed to increases in necessary health care in dogs.

Keywords: Canine; Genetic; Inherited; Morbidity; Mortality.

Fig. 1

Violin plot of Median F adjusted values across breeds. The percentage heterozygosity for 227 breeds or varieties was adjusted to an estimate of Wrights inbreeding coefficient-F_adj. Median and quartiles lines are indicated

Fig. 2

Morbidity by inbreeding levels. Morbidity values as VCE/10,000 dog years at risk (95% confidence intervals and mean are shown) plotted by mean F_adj within each breed in relevant categories. There were 11 breeds with F_adj < 0.125; mean morbidity for those breeds was 1282 (95% CI 1173–1391). For F_adj between 0.125 and 0.25, there were 66 breeds with a mean of 1537 (95% CI 1468–1606), and for F_adj over 0.25 there were 85 breeds with a mean of 1626 (95% CI 1562–1690). Significant differences for morbidity were identified between the three categories of F_adj using Kruskal-Wallis test (P = 0.0003). The relative risk morbidity compared to mixed breed dogs (F = 0 in dataset 1 and F_adj = 0.037 in dataset 2) for low inbred dogs was 1.01, meaning that they have a 1% increase in veterinary care events compared to mixed breed dogs. Breeds with inbreeding between 0.126 and 0.25 had a relative risk of 1.22 i.e. a 22% increase in veterinary care events while breeds with inbreeding over 0.25 had a relative risk of 1.29 i.e. a 29% increase in veterinary care events compared to mixed breed dogs

Fig. 3

Morbidity values within FCI groups. Violin plots of morbidity as number of veterinary care events/10,000 dog years at risk plotted by FCI group (95% Confidence intervals and mean are shown). FCI breed groupings are ordered from high mean morbidity on the left to low mean morbidity on the right. 2 = pinscher, schnauzer, molossoid, swiss mountain and cattle dogs, 8 = retrievers, 10 = sighthounds, 3 = terriers, 7 = pointing dogs, 1 = sheepdogs and cattledogs, 6 = scent hounds and dachshunds, 9 = companion and toy, and 5 = spitz and primitive types

Fig. 4

Morbidity as a function of body weight and inbreeding. Morbidity in number of veterinary care events /10,000 dog years at risk for breeds plotted by mid-range body weight. Regression lines are shown for different levels of inbreeding as indicated. As an example, the morbidity values for a 30 kg dog at no inbreeding (F_adj = 0) are predicted to be 1534.5 (SE 36.75) compared to high inbreeding (F_adj = 0.40) 1688 (SE 24.47) which is a 10% increase in veterinary care events. The morbidity value for a 5 kg dog at F = 0.25 is 1396.9 (SE 18.88) and for a 60 kg dog it is 1911.8 (SE 38.67), which is a 37% increase in veterinary care events