Herding trial results
Loss of hearing was reported by owners in herding strains of Border Collies. The loss of hearing appeared to be gradual, with distant hearing lost first. This was noticed in winning dogs that began to fail to respond to verbal commands when they were given from 200 m or more, but progressed to loss at 50 m. Luckily this form of deafness seems to be relatively rare, but occurred in some families.
An otoscopic examination was performed by a veterinarian to rule out any disease of the external ear and/or eardrum that may interfere with hearing. Border Collies with any sign of such disease were excluded from further study. All procedures were conducted according to the Canadian Council of Animal Care guidelines. A DNA cheek brush sample was taken from each dog for possible future study.
Two hundred and sixteen Border Collies were tested with the Brainstem auditory evoked response (BAER) hearing test at two herding trial events, one in Virginia and one in Pennsylvania. The stimulus intensity used was between 70 and 80 dB which is within the range recommended by the Orthopedic Foundation for Animals for their certification program. The BAER testing was performed at 21 Hz, which is within the effective range reported by Wilson et al.
[1].Eleven dogs were found to have hearing loss during this BAER testing at field trials. One was deaf in one ear, five were bilaterally deaf, and five had reduced hearing (Figure
1). One case of bilateral deafness in a 2.5 year old dog likely represents congenital deafness. The case of unilateral deafness occurred in a dog of 6 months. Five cases of hearing loss were found in dogs aged 7 to 11 and are believed to be of the adult onset type. Four of the 6 dogs between 12 and 15 years of age were ascribed as having geriatric hearing loss. Distinguishing the cause of deafness in the two dogs aged 10.5 and 11 years is not possible and including them in the adult-onset group instead of the geriatric onset group may be incorrect.
One hundred and twenty-eight of these 216 Border Collies were female and 88 were male. However, 4 of the dogs with hearing loss were female (3%) and 7 were male (8%).
Four additional dogs in this portion of the study were reported as having some hearing loss by their owners at 100 to 200 m. None of these four dogs were deaf with BAER testing at 70 dB, which is considered the estimated loudness of an alarm clock These dogs are likely in the early stages of hearing loss. However, all but one of the dogs found to have bilateral hearing loss by BAER testing at 70 dB, were also reported as having difficulty hearing at 50 m by their owners.
It was subsequently suggested that the four additional dogs suspected as deaf by their owners might have also tested as deaf with BAER testing at higher dB. In order to comply with Canadian Animal Care guidelines for studies of privately owned dogs, the veterinarian had to use dB below 85 dB since it has been reported that prolonged exposure to a stimulus of that intensity could lead to hearing damage.
None of the dogs with hearing loss were reported to have other health issues. Thus this type of deafness appears to be nonsyndromic.
Family studies
In another portion of this study, three families of Border Collies showed a pattern of adult onset deafness. Some dogs were BAER tested at more than one age, but most were tested only at the age indicated in Figure
2. However, the dog in Family 3 who is shown as deaf at 3 was based on owner report only. Not all BAER tests were conducted by the same veterinarian. An autosomal dominant pattern of inheritance appears to be the best fit (Figure
2). Variable expressivity in how and when deafness progresses is also typical of a dominant disorder
[2]. A more complex inheritance pattern, involving several genes, cannot be excluded.Another mating of a female that was deaf at 5 years of age and a male dog that was deaf at 7 years of age resulted in 3 pups, all still hearing in 2013 at 7 years of age by BAER testing (data not shown). However all 3 siblings were perceived as hard of hearing by their owners as early as 3 to 5 years of age, and their hearing loss appeared to gradually progress thereafter. Although these symptoms exclude that these dogs have congenital deafness, it does not exclude that they may become completely deaf. A similar mating of two deaf parents in Family 1 (Figure
2) suggests that not all pups will necessarily be deaf, excluding an autosomal recessive pattern of inheritance.