CANADIAN MANCHESTER TERRIER CLUB HEALTH SURVEY: DEAFNESS
In 2004/2005 the CMTC conducted a survey regarding hearing issues in Manchester Terriers. In total, 22 individuals responded to the survey. These individuals reported on a total of 424 Manchester Terriers (337 Toy Manchester Terriers, 87 standard Manchester Terriers). As can be noted, the vast majority of Manchester Terriers reported on were TMTs, a full 79% of the sample. For both varieties, data was reported for slightly more females than males (55% of both the TMT and SMT data was female). Respondents indicated that the majority of the Manchester Terriers being reported on suffered no hearing loss. Only slightly less than 6% of the sample, 25 individuals, were reported as having some form of hearing loss. In the 2002 CMTC/AMTC Health Survey, 15 Manchester Terriers, representing 1.46% of the animals reported on had some form of hearing loss. It is likely that the increase in the number of Manchester Terriers with hearing loss in the current survey reflects the fact that in the previous survey some individuals were reluctant to report hearing loss resulting from “normal aging processes”, whereas in the current survey it was clear that it was appropriate to report this form of hearing loss. The 25 individuals reported in the current survey to have hearing loss are the focus of the remainder of the report.
Distribution of Hearing Loss across Sex and Variety
The table below depicts the number of male and female animals of each variety who had reported hearing loss. Before looking at differences between males and females, or the varieties, it should be noted that there are sizable differences in the number of males and females and TMTs and SMTs in the survey and this affects the interpretation of the data.
TMT
SMT
Male
4
2
6
Female
13
6
19
17
8
For both TMTs and SMTs, a similar percentage of the sample had reported hearing loss; 5% of the TMT sample and 9% of the SMT sample. Because of the differences between the number of individuals of each variety included in the survey, it is unlikely that these small differences are meaningful. It seems far more likely that there are no significant differences between the varieties in terms of overall hearing loss.
When the number of males and females are considered slightly larger differences are found. Only 3% of the males in the sample had reported hearing loss, while 15% of the females did. However, before one concludes that there are sex differences in hearing loss, a number of factors must be considered. First, a larger number of females were reported on than males. This likely reflects the fact that breeders are more likely to keep a larger number of females than males. Based on later data, it also appears that these animals are kept into old age. It is possible, therefore, that this finding does not reflect a true sex difference, but rather reflects the fact that one consequence of aging is hearing loss and breeders may be more likely to keep a greater number of older female animals than older male animals and hence have a greater number of females with hearing loss to report on. The majority of individuals who reported animals with hearing loss reported data for many Manchester Terriers and were likely breeders.
Age of Onset
The average age of onset of hearing loss was late in life, at 8.94 years (SD=5.88). The age of onset ranged from birth to 15 years of age. Four individuals (25%) of the individuals in the survey were reported as being deaf from birth. One other individual also had early onset hearing loss, with deafness beginning at age 6. These 5 individuals represented the early onset hearing loss group. However for more than half of the respondents, onset was age 12 or later. No significant differences between sex or variety was found with regard to age of onset.
Type of Hearing Loss
The vast majority of individuals with hearing loss (96%) had bilateral hearing loss. Only one individual was reported with unilateral hearing loss.
Manner of Diagnosis
A question was included in the survey regarding who diagnosed the hearing loss. Most cases (76%) were reported as diagnosed by the breeder/owner. Only 6 cases (24%) were reported as having a diagnosis from a veterinarian.
Only 5 cases (20%) were reported as involving a BAER hearing test. The BAER test was performed only in those cases with early onset hearing loss (from birth to age 6). In addition, for 76% of the reported cases of hearing loss the respondents indicated no behavioural hearing tests were performed. When behavioural tests were reported, most indicated rather informal, unsystematic behavioural tests (e.g. calling the dog when out of eyesight).
Litter Information and Relatives with Hearing Loss
For Manchester Terriers with hearing loss, most respondents reported all other pups from the litter were healthy (60%) or they did not know about the status of other pups in the litter (35%). For only one individual suffering from hearing loss was there a reported mortality for other pups in the litter.
Nine respondents (36%) indicated other littermates also had hearing loss. It should be noted that three of these were individuals suffering from early onset hearing loss, and all 3 siblings were included in the survey.
For 5 individuals (20%) a sire who also suffered from hearing loss was reported. Another four (16%) had a dam who also had hearing loss. However, all of these cases involved late onset (after age 12) hearing loss.
Progression
No individuals were reported as having rapid hearing loss. The vast majority (84%) had slow onset hearing loss. Four individuals (16%) were reported as having hearing loss present from birth. Approximately 70% of the sample reported permanent hearing loss. Seven individuals (30%) reported regaining some hearing function. Of those individuals with early onset hearing loss, all but one were reported as regaining some hearing function.
Suspected Causes
The majority of hearing loss in Manchester Terriers was thought to be associated with aging. For 16 individuals (69%) the suspected cause of hearing loss was reported as being old age. Four individuals (19.4%) were reported as being congenital hearing loss. One individual’s hearing loss was reportedly the result of an injury, one other the result of illness, and a final individual’s hearing loss was the result of unknown causes. Very few individuals were exposed to several the potential risk factors for hearing loss (exposure to loud noises, exposure to medications known to cause hearing loss, and chronic ear infections). Only one Manchester Terrier in the survey was reported as suffering from chronic ear infections, however this animal was also reported as suffering from hearing loss.
Behavioural Responses
Very few deaf Manchester Terriers were reported as having negative behavioural responses associated with their hearing loss. No Manchester Terriers were reported as having balance problems. Only 4 individuals (16%) were reported as exhibiting a head tilt. Only 16 individuals responded to the item regarding an exaggerated startle response. For these 16 hearing impaired animals, half were reported as having an unusual startle response. Only 11 individuals responded to the items asking about aggressive responses to the startle response. Most Manchesters did not respond with any aggression. For those two individuals who did have an aggressive response a note indicated the individuals were quite dominant and the aggressive response was “snap”.
Other Comments from Respondents
“unable to process high pitch noise, slow recovery”
“believe it to be hereditary, how(ever) can’t prove it.”
“Nothing indicative that anything was abnormal until 5-6 weeks…re. MT3 – never had hearing loss that would have been noticed if not doing agility”
“She has been the only TMT to show any signs of deafness, and this didn’t start to show its head until she was a bit over 13 years old, and has gotten progressively more pronounced now that she is 15+ years old! She handles sign language beautifully with no problems whatsoever.”
“It is interesting to look at the relationship amongst those who developed the old age deafness – however not something I would modify my breeding program over, there are far worse problems to contend with than a 15 year old dog going deaf.”
Conclusions
The survey reveals that the majority of cases of deafness in Manchester Terriers are late onset, related primarily to older age. There are a few cases of early onset hearing loss which is disturbing and warrants watching in further surveys. But taken as a part of the overall whole, they do not represent a significant statistic at this time and there does not appear to a growth in that populations since the general health survey was conducted