Last year (2015) two interesting studies have been published, investigating the question if the olfactory ability of dogs is influenced by medication or other kinds of substances.
This question of is not of a purely academic nature. We all know those situations at gas stations, where gasoline vapors affect our own sense of smell. It is known that in humans a large number of substances can cause the total or partial loss of sensoric ability to detect scent (Hyposmie). Among others antihistamines, antidepressants, or ACE inhibitors, the inhalation of chlorine or benzene, or long-term contact with wooden or metal dust or smoke are known to induce this dysfunction. Lack of zinc can also be a reason; an important information which will be an interesting aspect further down in this article. (Wikipedia: Hyposmie)
In case substances really negatively affect the sense of smell of detection dogs, this would be an important factor in the use of drug, bomb or other kinds of detection dogs.
Standard medication metronidazole can have an influence on the olfactory ability
Certain diseases may also affect the olfactory ability – temporarily or irreversibly. The influence of drugs is another aspect, which might not immediately be apparent. Metronidazole and doxycycline are two widely-used antibiotics. End of 2015 the American Journal of Veterinary Research published the results of a study that examined the influence of these medications on the performance of explosives detection dogs. („Effects of oral administration of metronidazole and doxycycline on olfactory capabilities of explosives detection dogs„, American Journal of Veterinary Research, August 2016, vol. 77, pages 906-912, doi: 10.2460/ajvr.77.8.906)
Over a period of 10 days, one of these antibiotics was administered to 18 healthy explosives detection dogs, while their performance in the detection of standard explosives was examined in a standard test on the „Scentwheel“ on days 0, 5 and 10.
Under the influence of a normal dose of metronidazole, 9 of 18 dogs showed a significantly poorer detection rate for 2 out of 3 explosives. Metronidazole is known, that it has a negative impact on the sense of taste (associated with a specific metallic taste) in humans. It is assumed that metronidazole caused a reduced ability to smell and to detect odors (Hyposmie) in dogs, which is reversible.
No negative effects associated with doxycycline
In the same study no significant effect was found on the sense of smell in dogs under the influence of doxycycline. The authors expressly point out, that only labradors took part in their study. But it is assumed that no effect in the results would be identified if other breeds would have participated in the trial.
In summary this is an interesting study result with practical relevance for dog handlers with search and detection dogs: handlers shall avoid metronidazole if even a temporary degradation of the sense of smell is not acceptable. Doxycycline unfortunately is not an appropriate alternative medication. Both substances are used in different indications. In any case: it shall always be considered to take sick dogs out of service until full recovery.
In a second part of this article we will examine, how the sense of smell of dogs can be increase through special substances.