Researchers have developed what they describe as a simple and practical facial scale in horses to help assess the level of sedation.
Alice Rodrigues de Oliveira and her fellow researchers dubbed the scale FaceSed. It is based on elements of the Horse Grimace Scale.
Sedation and tranquilisation procedures in standing horses are alternatives to general anaesthesia to reduce the high anaesthesia-related mortality rate of about 0.9% in horses.
The study team, centred at São Paulo State University in Brazil, noted that different scales have been developed using scoring systems to qualify and quantify sedation in horses under the effect of sedative and tranquilisers.
However, the only objective measurement that does not require interpretation by the observer is head height above the ground, first used in 1991.
Other methods to assess depth and quality of sedation are subjective because their interpretation is based on the experience of the observer with the effects of sedation in horses.
Although facial characteristics are used to estimate horse sedation, there are no studies measuring their reliability and validity, they noted.
Because facial assessment is based only on observation, the development of a scale based on facial expression would avoid the limitations of other methods.
They described the work that led to the development of FaceSed, based on the adaptation and modification of three of the six facial action units that form part of the Horse Grimace Scale, used to assess pain.
To test FaceSed, seven horses were sedated at both high and low dose rates, with their faces photographed at baseline, peak, at the intermediate stage, and at the end of sedation.
The photos were randomised and sent to four veterinarian evaluators trained to assess the FaceSed items — ear position, eye opening, and relaxation of the lower and upper lips.
The scale appeared to work well. There was good agreement and consistency between the assessors, and the assessors individually delivered consistent results.
FaceSed, they said, proved to be a valid and reliable tool to assess tranquilisation and sedation in horses.
The horses presented higher scores at both the peak and intermediate phases of their tranquilisation/sedation, when compared to the start and end.
“The results of this study show that FaceSed is a simple and practical scale that offers reliability and validity to evaluate sedation over time in horses submitted to tranquilisation with acepromazine and sedation with the alpha-2 agonist detomidine with or without the opioid methadone,” they said.
The authors stressed that FaceSed was applied in the study by trained anaesthesiologists. “Further studies in clinical and other experimental scenarios and assessment by inexperienced observers may either confirm or not whether facial sedative characteristics evaluated on-site will present similar results.
“At this stage, FaceSed is a short, easy to apply scale and may be useful in clinical practice and in research purposes.”
The study team comprised Alice Rodrigues de Oliveira, Miguel Gozalo-Marcilla, Simone Katja Ringer, Stijn Schauvliege, Mariana Werneck Fonseca, Pedro Henrique Esteves Trindade, José Nicolau Prospero Puoli Filho and Stelio Pacca Loureiro Luna.
de Oliveira AR, Gozalo-Marcilla M, Ringer SK, Schauvliege S, Fonseca MW, Esteves Trindade PH, et al. (2021) Development and validation of the facial scale (FaceSed) to evaluate sedation in horses. PLoS ONE 16(6): e0251909. https://doi.org/10.1371/journal.pone.0251909