Reader Comments

Post a new comment on this article

Questions regarding case selection and IR calculation

Posted by DrBarker on 17 Oct 2013 at 19:26 GMT

I have general questions regarding case selection and IR calculation for this study.
1. Does the use of UCD cases affect case selection? For example, could MC presentation to UCD be unlikely given that private practices can generally handle this type of case? Would an owner of a neutered dog with MCT be more likely to accept a referral to UCD than the owner of an intact dog with MCT (i.e. would the MCT in the intact dog be more likely to be seen and treated at a private hospital and therefore not included in this study)?

2. Was there any analysis of demographic differences between clients presenting intact dogs and clients presenting neutered dogs? For example if most intact animals were used for breeding could it be possible that these dogs were pre-screened by owners and for example any dog failing OFA or Penn HIP certification then adopted as a pet and neutered, resulting in elimination of HD cases from the intact cohort and their transfer to the neutered cohort prior to an actual diagnosis of HD? Given that owners keeping dogs intact and owners preferring neutered dogs likely expose the dogs to different lifestyles and environments, was any effort made to characterize possible lifestyle differences between groups?

3. What measures were taken to ensure that the subjectivity of BCS determinations did not affect results? Who determined BCS, and when was BCS determined? How many dogs actually had accurate BCS determinations and at what ages were they evaluated? It would seem that BCS use is difficult in a prospective study, and significantly more difficult, less reliable and potentially mis-leading in a retro-spective study, yet BCS was used in statistical analysis in this study. What was the power of the study with regard to BCS?

4. Given the low actual numbers of cases representing incidence of disease in most groups, was any analysis of familial relationships between dogs in the study done?

5. The calculations involving late neutered cases seems problematic. My understanding is that a dog neutered at 48 months of age would be included in the intact group until 48 months of age, then included in the late neutered group until a diagnosis of a particular disease was made. If for example this dog developed CCL disease (CCL) at 54 months of age, would this not then add 4 CCL dog-years to the intact data with no incidence of disease, and one incident of disease with only 1/2 dog-year to the late neutered data? In addition would CCL be included as an incidence of disease in the neutered, not intact group. If this is true then it would seem the results could misrepresent a predisposition to CCL which could have occurred during the first 48 months of the dog's life, when the dog was intact.

6. Similarly could differences in timing of early neutering affect results? For example did a dog neutered at 11 months and diagnosed with HD at 16 months of age contribute 11 months to the intact disease free calculation and an incidence of one occurrence in 5 months of neutered status?

In general it would seem that a prospective controlled study would be more likely to provide reliable data regarding differences in disease incidence in intact vs. neutered dogs.

No competing interests declared.

RE: Questions regarding case selection and IR calculation

blhart replied to DrBarker on 22 Oct 2013 at 18:08 GMT

I will provide some general comments that apply to the list of questions and comments submitted.

The statement in the bottom line from this set of comments is that a controlled, prospective study would produce more reliable data. However, such a study would be impossible to conduct with 700-800 neutered or intact Golden Retrievers that would need to be randomly assigned to long-term homes and followed for 9 years. Our study followed standard epidemiological guidelines used in numerous studies on both humans and animals.

There is no basis for assuming that the dogs seen at the hospital in our UC Davis School of Veterinary Medicine are not representative of dogs of this breed in the general population, and as seen in private practices. In examining the records, we know that very few of the intact dogs were used in breeding. I have corresponded with the key leaders in the Golden Retriever Club regarding their information about dogs seen in private practices versus our UC Davis hospital, and they assured me that the dogs at both venues do not appear to differ in any aspect relative to our study. At our hospital, the diagnostic procedures for various diseases are standardized. This would not necessarily be the case if dogs from many private hospitals were used. Body condition scores (BCS), following standard hospital guidelines, and were not significantly related to which neutered dogs did, or did not get, a joint disorder. In general, while one may question the exact time frame used in the reference points for neutering dates and diagnoses, the same clinical diagnostic and statistical methodologies were applied to neutered and intact dogs alike; we report where we found significance.

Finally, and very important –as emphasized in our paper – every joint disorder and cancer where we found significant effects of neutering in one or both sexes, at one neutering age or another, has been already reported in at least one scientific journal to be significantly increased by neutering in studies that grouped breeds and neutering ages. We are not reporting anything new with regard to the diseases. In other words, there are no surprises in the disease effects we found. What our research does report, for the first time, is the occurrences of all of the diseases in one breed, as a function of sex and age at neutering. In addition to the scientific contributions, the long-term goal of our work is to offer those acquiring puppies some information so they can make informed choices with regard to the timing of neutering. The Golden Retriever is known for particular vulnerability to joint diseases and cancers; we fully expect to find differences among breeds with regard to specific diseases affected by various parameters of neutering.

No competing interests declared.