I.M.P. ? IMP Dogs (1990) [REPACK]
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The taste responses to the "umami" substances such as monosodium glutamate (MSG), GMP, and IMP were recorded from the chorda tympani nerve of mongrel dogs and beagles. A large synergism was observed between MSG and two species of nucleotides (GMP and IMP) in most mongrel dogs and between MSG and three species of nucleotides (GMP, IMP, and AMP) in beagles. The extent of the synergism between MSG and the nucleotides was much larger than that observed in any other animals examined except for humans. In the presence of GMP, the response magnitude of the chorda tympani nerve to MSG was increased but that to NaCl, HCl, sucrose, quinine, and glycine was unchanged. It was concluded that the canine taste responses to the umami substances closely resemble those in humans, and the dog is a suitable animal model for studies on the responses to the umami substances.
The births of domestic dogs with pigment deletion and associated congenital hearing and/or vision impairments are increasing, as a result of mutations of certain genes expressing popular coat colour patterns (Merle, piebald, Irish spotting). The future of these dogs is often pessimistic (early euthanasia or placement in rescues/fosters, lack of interactions and activities for adults). These pessimistic scenarios result from popular assumptions predicting that dogs with congenital hearing/vision impairments exhibit severe Merle-related health troubles (cardiac, skeletal, neurological), impairment-related behavioural troubles (aggressiveness, anxiety), and poor capacities to communicate, to be trained, and to be engaged in leisure or work activities. However, there is no direct scientific testing, and hence no evidence or refutation, of these assumptions. We therefore addressed an online questionnaire to owners of 223 congenitally sensory impaired (23 vision impaired, 63 hearing impaired, 137 hearing and vision impaired) and 217 sensory normal dogs from various countries. The sensory normal cohort was matched in age, lifetime with owner, breed and sex with the sensory impaired cohort, and was used as a baseline. The questionnaire assessed demographics, morphology, sensory impairments, health and behavioural troubles, activities, and dog-owner communication. Most hearing and/or vision impaired dogs exhibited abnormal pigment deletion in their coat and irises. Vision impaired dogs additionally exhibited ophthalmic abnormalities typically related to Merle. The results are opposed to all above-listed assumptions, except for neurological troubles, which were more frequently reported in sensory impaired dogs. However, we suggest that this finding could be partially accounted for by a lack of diagnosis of breed-related drug sensitivity and impairment-related compulsive behaviours. Results about communication and activities are particularly optimistic. The need for future studies of numerous dogs from various breeds tested for Merle, piebald and medical-drug-resistance genes, and the beneficial effects that present and future research may have on the future of sensory impaired dogs, are discussed.
Citation: Savel S, Sombé P (2020) Are dogs with congenital hearing and/or vision impairments so different from sensory normal dogs? A survey of demographics, morphology, health, behaviour, communication, and activities. PLoS ONE 15(9): e0230651.
In order to meet an increasing demand for pet dogs, most countries report growing numbers of dog breeders, atypical phenotypes in either existing or novel dog breeds, and births of puppies with various genetic defects . For example, the population of dogs with congenital hearing and/or vision impairments is increasing. This population results from the mutation of specific genes expressing popular patterns of coat colour.
Contrary to piebald, Irish spotting and KIT, Merle is additionally associated with various congenital ophthalmic abnormalities, referred to as Merle Ocular Dysgenesis. The most severe ophthalmic abnormalities are observed in double Merles. For these dogs, ophthalmic abnormalities can concern the eyeball (reduced size, called microphthalmia, or total absence), the cornea (microcornea), the iris (coloboma, hypoplasia), the size, shape, position or reaction of the pupil (starburst or misshapen pupil, dyscoria, corectopia), the pupillary membrane (persistence), the lens (cataract, microphakia, luxation), the sclera (coloboma, staphyloma), the retina (detachment, dysplasia), and the optic nerve [7, 8]. Depending on their severity, these ophthalmic abnormalities in double Merles can induce moderate to severe vision impairments, which are susceptible to worsen, or even to appear, over the life course.
It has long been assumed that the M locus has two possible alleles, namely non-merle (m, expressing solid phenotype) and Merle (M, expressing Merle phenotype). Latest research has identified between four and six variations of the Merle allele, as a function of the length of the poly-A tail of its SINE insertion [9, 10; 3]. The most detailed work is that conducted by Langevin and colleagues, who have tested hundreds of dogs from various breeds on the M locus and have determined six variations of the Merle allele [3, 4]. Their goals were to accurately determine which SINE insertion lengths can express a Merle pattern, which phenotype is most typically associated with each possible genotype, which cases of mosaicism can occur, and which breeding between genotypes are susceptible to produce excess white and sensory impaired, so-called double Merle, puppies. However, these genetics studies of Merle are very recent. The state-of-the-art equipment needed for precise examination of SINE insertion length and mosaicism is recent and expensive. Therefore, only two of the 16 laboratories that propose Merle testing in dogs can currently provide this detailed information in their test results. Few of the remaining laboratories provide state-of-the-art information about Merle genetics on their public websites . As a result, many dog breeders and owners are not fully aware of the complexity of Merle genetics and the conditions of at-risk breeding. Many countries have not yet strictly regulated Merle breeding. Comparable lack of information and regulation is observed for different breeds with piebald trait.
It is often assumed that excess white dogs, particularly double Merles, exhibit severe, or even lethal, health issues in their neurological, cardiac, skeletal and reproductive systems. Below, we propose three possible origins of these potentially false assumptions.
Second, the assumption of neurological issues in double Merles may originate in part from the fact that the most common neurological disorder in dogs, namely primary idiopathic epilepsy, is frequent in certain breeds from the herding group, such as Australian Shepherds and Border Collies . As specified above, these two breeds are most frequently concerned by the homozygous Merle genotype. The assumption of neurological issues may additionally, or even above all, result from the fact that Australian Shepherds and Border Collies are also frequently concerned by mutations of the medical drug resistance (MDR1) gene [14, 15]. As detailed further below, mutated MDR1 gene elicits neurotoxic, sometimes epileptiform reactions to common chemical agents (e.g., parasite control products) that are well tolerated by dogs with normal MDR1 gene. In other words, whether the neurological signs observed in double Merle Australian Shepherds and Border Collies are linked to their homozygous Merle genotype, as frequently assumed, or to breed-dependent epilepsy and MDR1 mutation, is undetermined.
Moreover, it is often assumed that congenitally deaf and/or blind dogs exhibit behavioural troubles (see foreword by Strain in ). Principally, their sensory impairment(s) are believed to increase frustration, and to elicit resultant aggressiveness and anxiety troubles. Also, it is assumed that deaf and/or blind dogs are particularly susceptible to bite, because they are easily startled when they are approached. Abnormal brain structures, and concomitant abnormal mental capacities, have also been assumed in congenitally deaf dogs. However, this assumption is based on a single neuro-imagery study that just reported a reduction in size of the auditory cortex in congenitally deaf Dalmatians .
In summary, above-mentioned assumptions predict that congenitally hearing and/or vision impaired dogs frequently exhibit health and behavioural troubles, and are poorly capable of communicating and practicing activities. These assumptions are so popular that they have drastic consequences on the future of sensory impaired puppies. However, there is to date no scientific evidence or refutation of these assumptions. Precisely, there is no study that we are aware of that directly assessed either health, behaviour, communication or activities in congenitally sensory impaired dogs, or that compared sensory impaired and sensory normal dogs on these points. One exception is the study by Farmer-Dougan and colleagues, who addressed a survey of behavioural traits to owners of hearing/vision impaired and sensory normal dogs . They found lower scores of aggressiveness and anxiety in the former cohort, which is opposite to the assumption.
To assess these different points, we chose to conduct an owner survey, a method that is frequently employed to assess, for example, health  and behaviour , in dogs. Surveys of dog owners have some disadvantages relative to the degrees of interest, understanding, recall and impartiality of the respondents, but have the following advantages: they allow the inclusion of dogs with much wider characteristics compared to surveys of veterinarians or animal insurance companies for questions on health, dog behaviourists for questions on behaviour, or canine clubs for questions on activities. In other words, owner surveys are not restricted to dogs with health/behavioural issues and activities. We chose the online diffusion of the questionnaire in two languages, namely French and English, in order to expand its geographic distribution. 2b1af7f3a8