October 30, 2017

Inherited defects in pedigree dogs. Part 1: Disorders related to breed standards

https://adelaidevet.com.au/pet-library/brachycephalic-obstructive-airway-syndrome-%E2%80%93-flat-nose-dogs

This article studies the negative effects of requirements of certain aspects of a dog’s body shape determined by the UK Kennel Club breed standards. An index was constructed to compare the severity of the disorders, which was “used to construct statistical analyses to determine the factors affecting reported breed predisposition to defects” (Asher 402). The Pug was one of the breeds found to have the “most associations with confirmation-related disorders” (204). This article is especially important when considering the severity of the pedigree-dog industry. There is much pressure to adhere strictly to the breed standard despite the health problems that may evolve. The purpose of this study is to “examine the number, prevalence and impact of disorders related to conformation aspects of the breed standards” (402).

Conformational breed-associated defects are not a new discovery, yet they continue to evolve due to phenotypic changes and modern changes to a dog’s environment. Some of these defects can be corrected by procedures and therefore result in less incentive to take action against harmful breeding. This research focuses on “inter-disorder comparisons,” instead of isolating the inherited disorders, in order to combine the clinical and epidemiological research. The additional goal of this review was to “develop a generic illness severity index for dogs (GISID) that could be applied to each disorder identified” (403). The study focused on the top 50 KC-registered breeds in the UK.

Three existing databases of inherited disorders in dogs were perused to create a comprehensive list of all inherited disorders in the top 50 breeds (403). Then more research was conducted to collect a database of data about the specifics of the inherited disorders, especially focusing on the primary organ system affected, details relevant to the prognosis, treatment, complications or impact on behavior, prevalence, age of onset, links with conformation, related disorders, and any other potentially relevant information. From this literature, a severity scoring system (Figure 1) was developed “to provide inter-disorder comparisons” (403). Disorders were classified as conformation-related (C) if the disorder directly resulted from a conformational trait, confirmation-inherited link (CD) if it was an inherited disorder made worse by a conformational trait, or as a non-conformational disorder (D) if the disorder was inherited, but was not due to conformational traits. These distinctions of disorders were totaled for each of the fifty breeds, and the severity scores were summed.

The results of the experiment displayed that the Pug had 33 total disorders (C + D + CD), 16 C disorders, and 2 CD disorders. The cumulative severity range for Cs and CDs for Pugs were 60-145 and 9-20 respectively. The Pug has also experienced one of the greatest relative increases in popularity since 1998 (up 449.1%), which then aids to the pressure of breeding to the standard at the cost of health. The Pug is the second highest breed after Miniature poodles to be predisposed to the most C disorders. Many of these disorders result from the brachycephalic head shape of the Pug, including stenotic nares, an elongated soft palate and hypoplastic trachea (406). A combination of these conditions is brachycephalic airway obstruction. Also, as dogs with protruding eyes, Pugs are more prone to ulceration or irritation of the eye. 17% of Pugs had keratopathy syndrome, which is chronic irritation of the surface of the eye. Although this issue is of low severity, it is a concern due to its high prevalence in certain breeds, especially the Pug.

Overall, the problem is in the breed standard. “By selecting for appearance rather than function or health, many breeds have become predisposed to health problems,” even going so far as to encourage breeders to select dogs predisposed to disease (409). This is especially relevant to the Pug:

Another example is the Pug. Breeds with screw-tails or curly tails are predisposed to spina bifida and hemivertebrae, but the breed standard for Pugs specifies that the tail should be ‘curled as tightly as possible over hip, double curl highly desirable’ (Kennel Club, 2008). The Pug breed club6 in the UK is aware of the high incidence of hemivertebrae in Pugs and has recommended that all dogs should be X-rayed before breeding. This move is laudable but will not eliminate the disorder if the breed standard is not altered (409).

The biggest accomplishment of this article is the establishment of a generic illness severity index for dogs (GISID), which “offers a framework for ethical and cost-effective decision-making in the care of dogs with inherited disorders and the debate around pedigree-dog breeding” (409). The main point of this article was to discuss the inherited disorders that stem from conformational traits, and to shed some light on breeding habits that ultimately are hurting the breed itself.

L. Asher, G. Diesel, J. Summers, P. McGreevy, L. Collins. “Inherited defects in pedigree dogs. Part 1: Disorders related to breed standards.” The Veterinary Journal, vol. 182, no. 3. Dec. 2009: 402-411. Web.

Original Article: http://www.sciencedirect.com/science/article/pii/S1090023309003645

Reviewed by Stephanie Lushniak