Performing the Small Animal Physical Examination by Ryane E. Englar

Author:Ryane E. Englar
Language: eng
Format: epub
Published: 2017-06-29T00:00:00+00:00

9.4 The Role of Scent

Of domestic species, dogs are equipped with the best olfactory capabilities. This acuity has been attributed to the amount of surface area devoted to olfaction: 7000 mm2 in dogs compared with 500 mm2 in people. Additionally, dogs have 2.8 × 108 olfactory cells, compared with 2.0 × 107 in humans [36].

Hence canine olfactory acuity is exquisitely sensitive. Even if a scent is diluted out to 1% of the strength that is detectable by people, scent recognition in the dog is possible [63]. This sensory perception is what makes it possible for dogs to detect fingerprints on glass 6 weeks after they were created [64] and to differentiate identical twins based upon olfaction alone [65]. A study involving police dogs demonstrated a 93.3% success rate in identifying individuals by scent [66]. In addition, the dogs could identify accurately the region of the body from where the scent originated [66].

Because scent recognition is strong in the dog, it is not surprising that pheromones play a significant role in canine communication [36]. Depending upon the individual dog and the intent behind its message, scent marking may include feces, anal sac secretions, urine, vaginal secretions, secretions from the merocrine sweat glands of the paw pads, and secretions from the sebaceous glands of interdigital skin [67].

Fecal marking is more common in males than females [68], but anal sac secretions coat every bowel movement of every dog with a unique identifier [36, 69]. In addition, anal sac secretions may be released when dogs are excited or anxious [36]. It is not uncommon for fearful dogs to express their anal glands at the veterinary clinic. This fishy, semi-rancid odor is unmistakably detectable by human members of the veterinary team in addition to any other dog in the vicinity.

Urine marking occurs more frequently than fecal marking, especially in free-ranging males [36]. Its purpose may be sexual, as a means to advertise sexual status or receptivity. However, more commonly, its context is social, providing information about the specific individual, its social group, and its social status [36, 70]. Around 50% of male dogs mark with urine by 13 months of age [71, 72], and by 24 months of age, 94% of all dogs, male and female, urine mark [72].

Scratching may or may not accompany urine and fecal marking. However, paw pad and interdigital secretions also carry identifiers and intra-species messages.

Vaginal secretions of receptive, intact females are more important than urine marking when it comes to attracting males [36].

Clearly, the canine nose is fine-tuned to detect a number of scents from a number of different regions of the body, all of which may carry messages of varying intent.

Working dogs make their living by employing their noses. Their function is reliant upon olfaction and their ability to discriminate between scents. It is for this reason that owners of tracking and/or field trial dogs prefer that the veterinary team avoid the administration of intra-nasal vaccinations whenever possible: these may cause the patient to display clinical signs that, although transient, may reduce olfactory acuity for up to 6 weeks [36].

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