Hip Dysplasia in Cavalier King Charles Spaniels
- - OFA Evaluation
- - PennHIP Method
- - Cornell's DLS Test
- - BVA/KC Scheme
- Breeders' Responsibilities
- Research News
- Related Links
- Veterinary Resources
Hip dysplasia (HD) is a heritable disease in cavalier King Charles spaniels which can cause the dogs terrible pain and debilitation. HD is the abnormal development of the hip, which can produce various degrees of arthritis (which also may be called degenerative joint disease, arthrosis, or osteoarthrosis). Estimates of affected CKCSs range from 12.4% to 25%.
Early symptoms of hip dysplasia include bunny hopping or swiveling the hips when running, having a difficult time rising from a down position or when climbing stairs. It is not predictable as to when or even if a dog with HD will start showing signs of lameness due to pain. There are many environmental factors, including caloric intake and the level of exercise, which can affect the severity of pain and lameness. Many dysplastic dogs with severe HD can run, jump, and play as if nothing is wrong, and other dogs with barely any HD x-ray indications are severely lame.
The only way to accurately diagnose HD is by radiography ( x-ray). Hip dysplasia is a developmental disease, meaning that it is not present at birth, but develops with age; it normally does not appear at all in x-rays of puppies or young cavaliers.
The Orthopedic Foundation for Animals (OFA) provides x-ray evaluations by panels of board certified veterinary radiologists. The PennHip method of hip joint analysis is an alternative means of diagnosing HD, also by x-ray.
According to OFA's statistics, 12.4% of all cavaliers are afflicted with hip dysplasia. However, the vast majority of cavalier breeders do not submit to OFA any x-rays of their breeding stock which show obviously dysplastic hips.* Therefore, OFA's statistics do not accurately reflect the incidence of HD in cavaliers. For example, only 5,896 cavaliers have been evaluated by OFA in the 37 years from 1974 through 2011 (only 370 in 2011). Considering that in 2008 alone, the AKC registered over 8,000 cavaliers, the OFA data base is woefully short. This indicates a major lack of interest by most all CKCS breeders in obtaining objective, expert evaluations of their dogs' hips.
*The Cavalier King Charles Spaniel Club,USA makes this comment on its website about the lack of submission of x-rays to OFA: "Since x-ray results are not always sent to OFA by breeders whose vets consider them dysplastic, this number is not exact and one can assume that 12.6% is a low figure."
OFA requires that dogs be at least 24 months old when x-rayed in order to qualify for a permanent OFA evaluation. OFA evaluates the x-rays by assigning a classification to each dog, from excellent, good, fair, borderline, mild, moderate, to severe. Ideally, breeders should consider x-raying their breeding stock again annually thereafter, as hip dysplasia has been found to be a progressive genetic disorder which results in deterioration of the hip joints after age two years.
It is believed by veterinary specialists in the field of hip dysplasia that the true incidence of HD in the cavalier King Charles spaniel probably is at least twice as high as those statistics would indicate, meaning 25% or more of all cavaliers.* Even higher percentages of cavaliers have been reported in recent studies of dogs requiring surgical hip procedures. See Veterinary Resources below. By comparison, OFA's current statistics show that 66% of pugs had dysplastic hips, 44.8% of Clumber spaniels, 30.4% of French bulldogs, and 19.7% of golden retrievers.
* A 2010 study of the PennHIP method, described below, also suggests that OFA scoring can underestimate the true incidence of hip dysplasia in dogs. In the April 1985 issue of Cornell University's Animal Health newsletter, it estimated that OFA's statistics under-state the true extent of hip dysplasia in a given breed by 1.5 times to 2.5 times, due to non-submissions to OFA of x-rays of obviously affected dogs.
The PennHip method was developed in 1983 by Dr. Gail K. Smith (right), an orthopedic surgeon at the University of Pennsylvania School of Veterinary Medicine. It measures hip joint laxity (looseness), which is the primary cause of degenerative joint disease. The Distraction Index (DI) used in the PennHip method is a measurement of passive hip laxity, the degree of looseness of the hip joint when the dog's hips are completely relaxed. Dogs with a DI of 0.3 have tighter hips and are less likely to develop hip dysplasia, and dogs with looser hips and DI values approaching 0.7 or more are at greater risk.
In a 2010 study conducted by Dr. Smith and others, they compared OFA and PennHIP evaluation results for 439 dogs from 1987 through 2008. The results showed that high percentages of dogs judged by OFA to be phenotypically normal nevertheless had clinically important passive hip joint laxity as determined by PennHIP's distraction radiography. The study concluded that dogs judged as "normal" by OFA can have clinically important passive hip joint laxity as determined by the PennHIP method. The results suggest that OFA scoring can underestimate susceptibility to osteoarthritis in dogs, which may impede progress in reducing or eliminating hip dysplasia through breeding.
You may contact Dr. Gail Smith at email email@example.com
Researchers at Cornell University's College of Veterinary Medicine have developed a new test for hip dysplasia, called the dorsolateral subluxation (DLS) test. The report that this procedure improves upon the OFA protocol by being more accurate at a younger age than the OFA test. Studies have shown the DLS test to be accurate as early as 8 months of age. The main difference between the DLS test and the OFA method is the way in which the dog is positioned while being x-rayed. While the OFA test places the hind limbs in a position that is not natural and may hide symptoms of hip dysplasia, the DLS test relies on a position much more similar to positioning normally found in a standing dog.
Before the DLS x-ray examination may take place, the dog must be anesthetized or deeply sedated. It is then placed on its stomach on a foam rubber pad. There is a hole cut in the pad for the dog’s hind legs. The stifles (corresponding to a human knee joint) make contact with the x-ray table, and the dog’s femurs are nearly perpendicular to the table. Arranging the dog in a position that mimics its natural posture allows the x-ray to show with a high level of accuracy what the position of the hip joints is.
Cornell's specialists explain that, in a normal hip joint, the head of the femur fits snugly into the joint socket, or acetabulum, but in the dysplastic joint, the femoral head conforms poorly to the acetabulum. More space is evident between the bones. Displacement of the femoral head is the hallmark of the disease. Joints are evaluated using the DLS score. This measurement, expressed as a percent, is calculated from the radiograph and represents the percent of the femoral head covered by the acetabular rim. The greater the coverage, the higher the DLS score, and the healthier the hip joint. The DLS test may be carried out by the dog's regular veterinarian. See details here.
The British Veterinary Association (BVA) and the UK's Kennel Club (KC) have instituted a hip dysplasia x-ray scheme for all breeds, which is similar to those of OFA and PennHIP. Details may be found at BVA's website here. Statistics for cavaliers under the BVA/KC hip scheme indicate that, as of October 2010, x-rays of only 270 CKCSs (compared to, e.g., over 70,000 Labrador retrievers) have been submitted for review under the scheme. Analysis of those x-rays show that the ratings of the UK cavaliers' hips ranged from "0" (no dysplasia) to "93" (severe dysplasia). See the BVA/KC statistics here.
Initial treatment is aimed at relieving pain and improving function with medication for the treatment of degenerative joint disease. If pain cannot be controlled there are surgical procedures (right) which may relieve pain and improve function in some dogs.
Stem cell therapy is being used on cavaliers by some practitioners, with reportedly successful results. See, e.g., this 2010 clinical report and this 2012 Paw Prints magazine article about a border collie, using Vet-Stem Regenerative Cell technology. In a 2007 study, in which dogs suffering from chronic osteoarthritis of the hip were treated with their own stems cells, the treated dogs "had significantly improved scores for lameness and the compiled scores for lameness pain, and range of motion compared with control dogs."
In a 2011 report, a team of Irish veterinary surgeons repaired the hips of 70 dogs with hip dysplasia (seven were CKCSs), using a "modified transarticular pinning technique". In a 2012 report, US surgeons, including Dr. Dominic Marino, reported on micro total hip prosthesis of 41 dogs, including six cavalier King Charles spaniels. In another 2012 report, the same US surgical team reviewed the outcomes of nano total hip replacement (NanoTHR) in twelve dogs, including a cavalier.
The Canine Inherited Disorders Database recommends that breeders breed only dogs that have disease-free joints and that come from ancestors with disease-free joints. The Canine Inherited Disorders Database further recommends not breeding any cavaliers whose offspring have hip dysplasia (dogs with hip dysplasia can produce normal offspring, and normal-appearing dogs can produce offspring with hip dysplasia).
The general principles recommended by OFA for breeding away from HD are:
1) Breed only normal dogs (meaning, not dysplastic) to normal dogs.
2) The normal dogs should come from normal parents and grandparents.
3) The normal dogs should have over seventy-five percent normal siblings.
4) A dog with excellent hips from a litter having more than twenty-five percent dysplastic pups is a worse breeding choice than a dog with fair hips from a litter experiencing less than twenty-five percent dysplasia.
5) Choose replacement dams that have better hips than their parents and the breed average.
Breeders should have their breeding cavaliers' hips x-rayed after age two years and have the x-rays evaluated by OFA before considering the dogs for breeding. Ideally, breeders should consider x-raying their breeding stock again annually thereafter, as hip dysplasia has been found to be a progressive genetic disorder which results in deterioration of the hip joints after age two years.
The Cavalier King Charles Spaniel Club, USA recommends that, prior to breeding any cavalier, the dog have a passing grade from an x-ray for hip dysplasia submitted to the OFA.
The Canine Health Information Center (CHIC) is a centralized canine health database sponsored by the AKC/Canine Health Foundation (AKC/CHF) and OFA. The CHIC, working with participating parent clubs, provides a resource for breeders and owners of purebred dogs to research and maintain information on the health issues prevalent in specific breeds.
AKC's national breed clubs establish the breed specific testing protocols. Dogs complying with the breed specific testing requirements are issued CHIC numbers. The ACKCSC requires that, to qualify for CHIC certification, cavaliers must be screened for hip dysplasia, using the OFA, PennHIP, or OVC protocol.
February 2013: Early neutering may affect male dogs' risk for developing hip dysplasia. A University of California at Davis study of golden retrievers has found that early castration was associated with an increase in the occurrence of hip dysplasia. The study showed a surprising 100 percent increase, or doubling, of the incidence of hip dysplasia among early-neutered males. Earlier studies had reported a 17 percent increase among all neutered dogs compared to all non-neutered dogs, indicating the importance of the new study in making gender and age-of-neutering comparisons.
September 2010: PennHIP's Dr. Gail Smith finds "OFA Normal" dogs have hip joint laxity. In a 2010 study, Dr. Gail K. Smith, an orthopedic surgeon at the University of Pennsylvania School of Veterinary Medicine who developed the PennHIP method of testing dogs' for hip dysplasia, and others compared OFA and PennHIP evaluation results for 439 dogs from 1987 through 2008. The results showed that high percentages of dogs judged by OFA to be phenotypically normal nevertheless had clinically important passive hip joint laxity as determined by PennHIP's distraction radiography. The study concluded that dogs judged as "normal" by OFA can have clinically important passive hip joint laxity as determined by the PennHIP method. The results suggest that OFA scoring can underestimate susceptibility to osteoarthritis in dogs, which may impede progress in reducing or eliminating hip dysplasia through breeding. You may contact Dr. Gail Smith at email firstname.lastname@example.org
Hip Dysplasia, Chapter 83, Textbook of Small Animal Orthopedics. Wayne H. Riser, W. Harker Rhodes, and Charles D. Newton. 1982; U. Penn CAL small animal orthopedics.
Control of Canine Genetic Diseases. Padgett, G.A., Howell Book House 1998, pp. 198-199, 245.
Canine Inherited Disorders Database: http://ic.upei.ca/cidd/disorder/hip-dysplasia
Effect of Adipose-Derived Mesenchymal Stem and Regenerative Cells on Lameness in Dogs with Chronic Osteoarthritis of the Coxofemoral Joints: A Randomized, Double-Blinded, Multicenter, Controlled Trial. Linda L. Black, James Gaynor, Dean Gahring, Cheryl Adams, Dennis Aron, Susan Harmon, Daniel A. Gingerich, and Robert Harman. Vety. Therapeutics. 2007; 8(4). Quote: "Autologous stem cell therapy in the field of regenerative veterinary mediciine involves harvesting tissue, such as fat, from the patient, isolating the stem and regenerative cells, and administering the cells back to the patient. Autologous adipose-derived stem cell therapy has been commercially available since 2003, and the current study evaluated such therapy in dogs with chronic osteoarthritis of the hip. Dogs treated with adipose-derived stem cell therapy had significantly improved scores for lameness and the compiled scores for lameness pain, and range of motion compared with control dogs. This is the first randomized, blinded, placebo-controlled clinical trial reporting on the effectiveness of stem cell therapy in dogs."
Evaluation of the relationship between Orthopedic Foundation for Animals' hip joint scores and PennHIP distraction index values in dogs. Michelle Y. Powers, Georga T. Karbe, Thomas P. Gregor, Pamela McKelvie, William T. N. Culp, Hilary H. Fordyce, and Gail K. Smith. JAVMA Sept 2010; 237(5):532-541. Quote: "Objective—To compare 2 screening methods for detecting evidence of hip dysplasia (Orthopedic Foundation for Animals [OFA] and PennHIP) in dogs. 439 dogs ≥ 24 months of age [Cavalier King Charles spaniel included] that received routine hip joint screening from June 1987 through July 2008. Dogs were sedated, and PennHIP radiography was performed (hip joint– extended [HE], compression, and distraction radiographic views). The HE radiographic view was submitted for OFA evaluation. A copy of the HE radiographic view plus the compression and distraction radiographic views were submitted for routine PennHIP evaluation, including quantification of hip joint laxity via the distraction index (DI). Results: 14% (60/439) of dogs had hip joints scored as excellent by OFA standards; however, 52% (31/60) of those had a DI ≥ 0.30 (range, 0.14 to 0.61). Eighty-two percent of (183/223) dogs with OFA-rated good hip joints had a DI ≥ 0.30 (range, 0.10 to 0.77), and 94% (79/84) of dogs with OFA-rated fair hip joints had a DI ≥ 0.30 (range, 0.14 to 0.77). Of all dogs with fair to excellent hip joints by OFA standards, 80% (293/367) had a DI ≥ 0.30. All dogs with OFA-rated borderline hip joints or mild, moderate, or severe hip dysplasia had a DI ≥ 0.30 (range, 0.30 to 0.83). Conclusion and Clinical Relevance: Dogs judged as phenotypically normal by the OFA harbored clinically important passive hip joint laxity as determined via distraction radiography. Results suggested that OFA scoring of HE radiographs underestimated susceptibility to osteoarthritis in dogs, which may impede progress in reducing or eliminating hip dysplasia through breeding."
Treatment of 70 dogs with traumatic hip luxation using a modified transarticular pinning technique. W. McCartney, K. Kiss, F. McGovern. Vet.Rec. Mar 2011; 168(13):355. "Luxation of the hip is the most common joint luxation in dogs. Treatment options are based on closed reduction, or surgical reduction and stabilisation using intra-articular or extra-articular methods. The intra-articular techniques include toggle pin variations or transarticular pinning, whereas the extra-articular techniques include de Vita pinning and extracapsular prosthesis. This short communication describes an analysis of 70 cases of traumatic hip luxation in dogs treated with a modified transarticular pinning technique. Seventy dogs were operated on for hip luxation between 2003 and 2009. The predominant breeds were labrador retriever (13), collie (10), golden retriever (nine), German shepherd dog (eight), Cavalier King Charles spaniel (CKCS) (seven) and mixed breed (12). The remaining 11 dogs were poodles (two), Staffordshire bull terriers... A retrospective analysis of hip luxation case details was undertaken in conjunction with a telephone questionnaire survey of the owners; all 70 dogs had sufficient data for analysis. Dogs with underlying hip dysplasia or osteoarthritis did not have transarticular pinning performed as a treatment for hip luxation. Only cases in which an outcome assessment had been made using the owner questionnaire more than six months postoperatively were included. Two questions were asked in the questionnaire. For the first, ‘Is your dog stiff or lame at any time and if so can you grade it as frequent, intermittent or never?’, frequent was described as more than three times a day, intermittent as up to three times a week and never as no lameness or stiffness at anytime. For the second, ‘Are you satisfied with the outcome?’, there were two possible answers – ‘satisfied’ and ‘not satisfied’. On the basis of the owner's repsonses, the outcome was graded as failed, poor, good or excellent. The outcome grading was classified as excellent if a dog had no complications and was not stiff or lame at any time, good if the dog was only intermittently stiff or lame up to three times a week, poor if there was frequent (daily) lameness or stiffness, and failed if there were any serious complications. There were 33 females and 37 males, and the age range was six months to 11 years."
Treatment of hip dysplasia. A. Anderson. J.Sm.Anim.Prac. April 2011;52(4):182-189. Quote: "Hip dysplasia is a common orthopaedic developmental disorder of dogs. This paper reviews the treatment options available for management of the condition in the skeletally immature and adult dog."
Micro Total Hip Replacement in Dogs and Cats. Dominic J Marino, Shadi J Ireifej DVM, Catherine A Loughin. Vet. Sur. Jan 2012; 41(1):121-129. Quote: "Objective: To describe the surgical technique using power-assisted femoral preparation and clinical outcome in 41 dogs and 2 cats surgically treated with the micro total hip prosthesis. Animals: Dogs (n = 41[cavalier King Charles spaniels = 6]) and 2 cats. Results: Six dogs had staged bilateral MicroTHR, 35 dogs and 2 cats had unilateral MicroTHR. Median body weight was 8.2 kg (range, 2.1–14.2 kg) whereas for those that had complications (fracture or luxation) it was 8.6 kg (range, 6.6–14.1 kg). Median operative time was 71 minutes (range, 55–105 minutes). Complications included luxations (5 of 49; 10%) and femoral fracture (1; 2%). Lameness grades assigned at the 3-month recheck examination: 39 (80%) animals were grade 1, 6 (12%) were grade 2, and 4 (8%) were grade 3. Forty-five animals (92%) had good or excellent results. Conclusions: MicroTHR is a practical and effective surgery in small breed dogs and cats with coxofemoral disease."
Nano Total Hip Replacement in 12 Dogs. Shadi Ireifej, Dominic Marino, Catherine Loughin. Vet. Sur. Jan 2012; 41(1):130-135. Quote: "Objective: To determine the short-term clinical outcome of nano total hip replacement (NanoTHR) in dogs. Results: Breeds were Yorkshire Terriers (n = 6), Toy Poodles (2), with 1 each of Maltese, Pomeranian, Cavalier King Charles Spaniel, and Shih-Tzu. Median body was 4.87 kg (range, 2.5–5.90 kg) and median age, 35.75 months (range, 12–144 months). Radiographs were taken in 4 dogs at 12 days (n = 2), 14 days (1), and 30 days (1) after surgery because of presentation for an acute grade 5 lameness. Three dogs had femoral fractures distal to the femoral implant tip and 1 dog displaced the acetabular implant medially. After revision surgery, all femoral fractures were assessed as healed with intact plate fixation. The dog with the medially displaced acetabular component responded to conservative management including strict confinement and analgesic administration. Eight dogs (58%) were assigned a grade 1 lameness and 4 dogs were grade 2 (33%) at 12-week examination. The 3 dogs with grade 5 lameness scores found to have femoral fractures within 1 month after surgery, subsequently improved to grade 1 (n = 1) and 2 (2) 12 weeks after revision surgery. The dog with medial acetabular displacement improved to a grade 2 lameness 12 weeks after conservative management. Conclusions: Although all 12 dogs had good-to-excellent outcomes, 33% experienced significant complications associated with the technique. As improvements in instrumentation and refinements in the technique are developed, NanoTHR can be considered an alternative to the femoral head and neck ostectomy (FHO) or medical management of coxofemoral disease for toy breed dogs. Further studies with a larger number of dogs and longer follow-up times are required."
Neutering Dogs: Effects on Joint Disorders and Cancers in Golden Retrievers. Gretel Torres de la Riva, Benjamin L. Hart, Thomas B. Farver, Anita M. Oberbauer, Locksley L. McV Messam, Neil Willits, Lynette A. Hart. PLOSone. Feb. 2013. Excerpt: "Hip Dysplasia: Perusal of Figure 1 and Table 4 reveals that HD in early-neutered males, affecting 10.3 percent, was more than double the proportion of intact males with the disorder, which was 5.1 percent, a significant difference (K-M: p<0.01). There was also a significant difference between early and late neutering in males (K-M: p<0.05). The mean ages of HD onset for intact, early-neutered, and late-neutered male dogs were 4.4, 3.6, and 4.7 years, respectively. No difference was found between early-neutered dogs with and without HD when compared with respect to their BCS, (means 6.1 and 5.7, respectively; CPH: p = 0.22). No other comparisons of HD occurrence were significant; HD was not increased in occurrence by early or later neutering in females (Figure 2). ... While neutering is expected to lead to a greater gain in body weight than in intact dogs , , the BCS of early-neutered dogs with the disorders and the early neutered comparison groups without the disorders were not significantly different – and, in fact quite similar – indicating that weight on the joint was not a major determinant in the occurrence of these joint disorders. Using the CPH model to compare early-neutered with intact dogs, for both HD and CCL, neither neutering status nor BCS was significant, indicating that the two factors are fairly highly confounded. This implies that the occurrence of HD and CCL in early-neutered dogs is a combined function of the effect of neutering on growth plates, as well as the increase in weight on the joints brought on by neutering. As mentioned, when only early-neutered dogs with and without HD or CCL were compared with respect to their BCS, no differences were found between early-neutered males with and without these joint disorders. ... As for the pathophysiological reasons for the joint disorders, one can point to the role of gonadal hormones in controlling the closure of bone growth plates , . An atypical growth plate closure, resulting from the absence of gonadal hormones, may increase the chance of a clinically apparent joint disorder, such as HD. ... Confounding factors that may influence the nature of a neuter-related joint disorder are the breed-specific gender vulnerabilities, including growth rate differences, as well as the timing of growth plate closure, which occurs more quickly in males than in females. In the males of this study, the occurrence of HD was doubled in the cases with early androgen removal as compared with intact males, but in females, removal of the ovaries did not appear to be associated with an increased likelihood of HD. This presumably reflects the effect of gender on growth-plate development."
Comparative analyses of genetic trends and prospects for selection against hip and elbow dysplasia in 15 UK dog breeds. Lewis TW, Blott SC, Woolliams JA. BMC Genet March 2013;14:16. Quote: "Background: Hip dysplasia remains one of the most serious hereditary diseases occurring in dogs despite long-standing evaluation schemes designed to aid selection for healthy joints. Many researchers have recommended the use of estimated breeding values (EBV) to improve the rate of genetic progress from selection against hip and elbow dysplasia (another common developmental orthopaedic disorder), but few have empirically quantified the benefits of their use. This study aimed to both determine recent genetic trends in hip and elbow dysplasia, and evaluate the potential improvements in response to selection that publication of EBV for such diseases would provide, across a wide range of pure-bred dog breeds. Results: The genetic trend with respect to hip and elbow condition due to phenotypic selection had improved in all breeds, except the Siberian Husky. However, derived selection intensities are extremely weak, equivalent to excluding less than a maximum of 18% of the highest risk animals from breeding. EBV for hip and elbow score were predicted to be on average between 1.16 and 1.34 times more accurate than selection on individual or both parental phenotypes. Additionally, compared to the proportion of juvenile animals with both parental phenotypes, the proportion with EBV of a greater accuracy than selection on such phenotypes increased by up to 3-fold for hip score and up to 13-fold for elbow score. Conclusions: EBV are shown to be both more accurate and abundant than phenotype, providing more reliable information on the genetic risk of disease for a greater proportion of the population. Because the accuracy of selection is directly related to genetic progress, use of EBV can be expected to benefit selection for the improvement of canine health and welfare. Public availability of EBV for hip score for the fifteen breeds included in this study will provide information on the genetic risk of disease in nearly a third of all dogs annually registered by the UK Kennel Club, with in excess of a quarter having an EBV for elbow score as well."
Estimated Breeding Values for Canine Hip Dysplasia Radiographic Traits in a Cohort of Australian German Shepherd Dogs. Bethany J. Wilson, Frank W. Nicholas, John W. James, Claire M. Wade, and Peter C. Thomson. PLoS One Oct. 2013;8(10):e77470. Quote: "Canine hip dysplasia (CHD) is a serious and common musculoskeletal disease of pedigree dogs and therefore represents both an important welfare concern and an imperative breeding priority. The typical heritability estimates for radiographic CHD traits suggest that the accuracy of breeding dog selection could be substantially improved by the use of estimated breeding values (EBVs) in place of selection based on phenotypes of individuals. The British Veterinary Association/Kennel Club scoring method is a complex measure composed of nine bilateral ordinal traits, intended to evaluate both early and late dysplastic changes. However, the ordinal nature of the traits may represent a technical challenge for calculation of EBVs using linear methods. The purpose of the current study was to calculate EBVs of British Veterinary Association/Kennel Club traits in the Australian population of German Shepherd Dogs, using linear (both as individual traits and a summed phenotype), binary and ordinal methods to determine the optimal method for EBV calculation. Ordinal EBVs correlated well with linear EBVs (r=0.90–0.99) and somewhat well with EBVs for the sum of the individual traits (r=0.58–0.92). Correlation of ordinal and binary EBVs varied widely (r=0.24–0.99) depending on the trait and cut-point considered. The ordinal EBVs have increased accuracy (0.48–0.69) of selection compared with accuracies from individual phenotype-based selection (0.40–0.52). Despite the high correlations between linear and ordinal EBVs, the underlying relationship between EBVs calculated by the two methods was not always linear, leading us to suggest that ordinal models should be used wherever possible. As the population of German Shepherd Dogs which was studied was purportedly under selection for the traits studied, we examined the EBVs for evidence of a genetic trend in these traits and found substantial genetic improvement over time. This study suggests the use of ordinal EBVs could increase the rate of genetic improvement in this population."
Assessing the impact of genomic selection against hip dysplasia in the Labrador Retriever dog. E. Sánchez-Molano, J.A. Woolliams, S.C. Blott, P. Wiener. J. Anim. Breeding & Genetics. April 2014;131(2):134-145. Quote: "Many purebred dogs exhibit a higher prevalence of inherited diseases compared with non-purebred dogs. One of the most popular breeds in the UK is the Labrador Retriever, which has a high prevalence of hip dysplasia resulting in high costs for surgical operations and impaired animal welfare. Considering the many complications of highly managed populations, mainly due to breeder's conventions and the resulting population structure, is of great importance for the proper development of a strategy against the disease. In this study, we have compared the utilities and performances of both genomic and phenotypic selection against hip dysplasia in a simulated population with the characteristics of the British Veterinary Association and Kennel Club (BVA/KC) hip dysplasia scheme. The results confirm the potential benefits of genomic selection by showing a moderate increase of 1.15-fold (assuming a realistic accuracy of r2 = 0.5) in response to selection due to the higher accuracy (between 0.96- and 1.32-fold, considering 0.35 ≤ r2 ≤ 0.7) and more than a threefold increase when all the offspring in each litter are tested (between 3.25- and 4.55-fold, again considering 0.35 ≤ r2 ≤ 0.7)."