New protocol standardizes recording of lip-related pigment changes and lesions in horses

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The diagram indicates the relationship between affected anatomical areas, the observed natural pigmentation of the mouth, and the types of potentially or definitely pathological findings recorded.
The diagram indicates the relationship between affected anatomical areas, the observed natural pigmentation of the mouth, and the types of potentially or definitely pathological findings recorded. Image: Uldahl et al. https://doi.org/10.3390/ani12050643

A standardized system for documenting pigmentation changes and evidence of injuries around the corner of the lips in horses has been developed by researchers.

The Oral Commissure Assessment Protocol is described by Mette Uldahl and her fellow researchers in the open-access journal Animals.

They set out to develop a protocol to categorize and record pathological findings around the lip commissures, with a focus on lesions caused by the bit. Since the bit lies in or close to the oral commissures, it is a common site for bit-related lesions.

A convenience sample of 206 horses presented for routine dental examinations were sedated. In each case, the mouth was held open with a gag, and photographs were taken of the oral commissures and nearby lip areas.

The horses were divided into two groups: Those that had never been bitted and those currently or previously bitted. In addition, the owners completed a questionnaire describing the horse’s name, identification number, breed, age, sex, color, training level, and discipline.

To develop the protocol, the photographs were analyzed in a systematic manner, and a score chart was developed to standardize the reporting of lesions.

First, the precise anatomical location was defined. Second, pigmentation was classified as natural or potentially pathological. Third, any pathological lesions were characterized.

Anatomical locations around the commissures were mapped precisely and coded 1 to 21 to distinguish between the involvement of skin, mucosa or both at each site. The assigned numbers identify specific locations and do not indicate the severity of the findings.

Findings, categorised as either natural pigmentation changes, potentially pathological pigment changes, scarring, contusions or erosions, or bleeding, were recorded for each location. The presence or absence of lesions was scored for each area, with 0 indicating their absence.

The researchers found that naturally occurring light or mottled pigmentation at the commissures of the lips was present in 135 of the 206 horses.

Potentially pathological pigment changes occurred more frequently in horses with a higher level of training and in light-coloured horses, but were not associated with current bit use or the discipline in which the horse participated.

Scars were more frequent in horses competing at a higher level.

Examples of natural pigmentation colours and patterns. (A) Light with no mottled pigmentation. (B) Dark with no mottled pigmentation. (C) Light mucosa, dark skin, no mottled pigmentation. (D) Dark with mottled pigmentation of the skin and mucosa in area 1–3. (E) Dark with mottled pigmentation of the skin in area 1 + 3. (F) Light mucosa, dark skin, mottled pigmentation of mucosa area 2. (G) Light mucosa, dark skin, mottled pigmentation of mucosa and skin area 1–3. (H) Light mucosa, dark skin, mottled pigmentation of mucosa and skin area 1–3. Image: Uldahl et al. https://doi.org/10.3390/ani12050643
Examples of natural pigmentation colours and patterns. (A) Light with no mottled pigmentation. (B) Dark with no mottled pigmentation. (C) Light mucosa, dark skin, no mottled pigmentation. (D) Dark with mottled pigmentation of the skin and mucosa in area 1–3. (E) Dark with mottled pigmentation of the skin in area 1 + 3. (F) Light mucosa, dark skin, mottled pigmentation of mucosa area 2. (G) Light mucosa, dark skin, mottled pigmentation of mucosa and skin area 1–3. (H) Light mucosa, dark skin, mottled pigmentation of mucosa and skin area 1–3. Image: Uldahl et al. https://doi.org/10.3390/ani12050643

In all, only two horses had contusions or erosions, five had ulcers, and none showed bleeding. The numbers were too low for statistical analysis, they said.

The study team said their consistent and thorough protocol provides a detailed method for categorizing and recording lesions in and around the corners of the lips, including natural changes and those most likely arising from bit use.

It could, they said, be employed to document findings in relation to the governance of horse welfare in sport.

While sedation was employed in the study, the protocol can equally be used for inspections on-site at competitions without sedation or the use of a gag.

“The structure of the protocol allows the user to focus only on pigmentation, scars or lesions if that is the scope of the current investigation,” they said.

“If the exact location of the findings is not of interest, the anatomical location score can be ignored, and observations assigned to just the left and right side.”

Some oral lesions can be seen as historical markers of previous bit use while others are acute and indicate recent or current use, they said. “More information is needed regarding the interpretation of what each lesion means in relation to equine management,” they added.

“The availability of defined protocols and lesion classifications for evaluating and describing oral lesions in horses will help equestrian sport governing bodies, veterinary practitioners and researchers to report their findings in a standardized manner that facilitates making comparisons between different populations and studies.”

The authors said their study showed that there is great variability in the natural appearance of the mouth, with overall light pigmentation or mottled, irregular pigmentation patterns being very common, and usually bilateral.

Potentially pathological pigment changes caused by the bit were recognized as clearly demarcated circular or linear areas of lighter pigment in the oral commissures and adjacent lips.

The researchers noted that, on rare occasions, horses that had never been bitted presented with pigment spots resembling potentially pathological pigment changes associated with bit use.

“This makes it difficult to identify whether pigment changes are a consequence of bit use in an individual horse.”

Scars, they said, were reliable markers of previous problems with bit use at individual and population levels, but surface roughness was not.

“The validity of contusions and erosions being indicative of problems with the bit was questionable, because the numbers were too low for statistical analysis, and they were encountered in horses that were not being bitted.”

Ulcers, they said, were the key finding in relation to the assessment of current bitting problems. “Their presence indicates current and previous discomfort and pain during the development of the lesion, which warrants further attention.”

Although ulcers were not associated with bleeding, it is recommended that bleeding should remain in the oral evaluation protocol because its presence always indicates a need for further investigation.

They said validation of the predictive value and overall reliability of findings at both individual and population levels are needed before examination of the oral commissures can be used as an evidence-based screening tool to evaluate bit-related problems and equine welfare.

The use of the protocol in future research will add to the significance of the findings in this study and, in the long term, help to determine the distribution of natural pigmentation and pathological changes of the oral commissure in the horse population.

The full study team comprised Uldahl, with the Vejle Equine Practice in Fasanvej, Denmark; Louise Bundgaard, with the Department of Veterinary Clinical Sciences at the University of Copenhagen; Jan Dahl, with Jan Dahl Consult in Ugerløse, Denmark; and Hilary Mary Clayton, with Sport Horse Science, in Mason, Michigan.

Uldahl, M.; Bundgaard, L.; Dahl, J.; Clayton, H.M. Assessment of Skin and Mucosa at the Equine Oral Commissures to Assess Pathology from Bit Wear: The Oral Commissure Assessment Protocol (OCA) for Analysis and Categorisation of Oral Commissures. Animals 2022, 12, 643. https://doi.org/10.3390/ani12050643

The study, published under a Creative Commons License, can be read here

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