Are mares stresssed by rectal exams?

Mares that are accustomed to rectal examinations do not show physiological signs of stress, when examined by vet students, recent research shows.

Rectal examination is a vital tool in equine medicine – both for the investigation of gastrointestinal problems such as colic and in the routine management of assisted breeding in mares.

It is, however, a technique not without risks for both the horse and the operator. Horses appear to be more at risk of serious consequences such as rectal tears compared to other species.

In research conducted at the University of Pretoria, Elize van Vollenhoven and colleagues assessed the stress response of mares subjected to rectal examination. These were Nooitgedacht pony mares that were accustomed to rectal examination. 

The procedure (trans-rectal palpation by a veterinary student) lasted 20 minutes for each horse. Samples of faeces and saliva were collected before and after the procedure and tested for salivary glutocorticoids (sGC) and faecal glucocorticoid metabolites (fGCM) respectively.

The research team found no significant differences in median sGC concentrations before palpation and at 10, 40, and 70 minutes after palpation. Neither were there significant differences between median fGCM concentrations before and 26 hours after palpation. 

The authors of the report conclude that student transrectal palpation of the reproductive tract in habituated mares did not activate the hypothalamic-pituitary-adrenal axis.

For more details, see:

Salivary Glucocorticoid and Fecal Glucocorticoid Metabolite Concentrations in Pony Mares During Transrectal Palpation of the Reproductive Tract by Veterinary Students

Elize van Vollenhoven, Catharina Cornelia Grant, Lizelle Fletcher, Martin Lance Schulman, Patrick Collin Page, André Ganswindt.

Journal of Equine Veterinary Science (2018) 70, pp 7-12

https://doi.org/10.1016/j.jevs.2018.07.010

Genipin – a possible new treatment for DDSP

A possible new treatment for dorsal displacement of the soft palate has been suggested by recent research.

In the normal horse, the soft palate fits snugly around the base of the epiglottis (the front part of the larynx). This allows inhaled air to pass directly from the nasal passages into the trachea. Normally, the horse does not breathe through its mouth. This arrangement of the epiglottis and soft palate has been described as being like a button in a buttonhole.

When the horse swallows, the opening of the larynx closes and the soft palate moves up, allowing food to pass from the mouth into the oesophagus without entering the trachea. Once the bolus of food has passed, the larynx fits back in position in the buttonhole.

Dorsal displacement of the soft palate (DDSP) occurs when the soft palate becomes dislodged from its normal position around the base of the epiglottis and rests on top of the epiglottis, in the laryngeal opening. When this occurs during high speed exercise, the high air flow causes the free border of the soft palate to vibrate. This causes significant obstruction to the horse’s breathing and produces a gurgling sound. The horse usually has to slow down and swallow to replace the soft palate in its normal position.

Humans also suffer problems associated with the soft palate – snoring, perhaps most troublesome for those not affected, and the potentially life-threatening condition,

obstructive sleep apnoea.

In horses, numerous therapies have been used, ranging from tying down the tongue during races to surgical intervention to tie the larynx forward, and including techniques to stiffen the soft palate such as laser treatment and firing.

Now a recent study has examined modifying the mechanical properties of the soft palate by injecting genipin, a minimally toxic, protein crosslinker extracted from the Gardenia jasminoides plant. The study featured horses but also considered potential implications for the treatment of snoring and obstructive sleep apnoea in humans.

The research, by Stephanie Hunt of the Biomedical Engineering Department of the University of Kentucky, Lexington and colleagues is reported in the International Journal of Biomaterials.

The research team looked at the effect of genipin on the mechanical properties of soft palate tissue and demonstrated that genipin-injected soft palates had reduced vibration amplitude and flaccidity and increased strength compared with untreated palates.

They also carried out a small pilot study to assess the effect of genpin-injection in normal horses and in horses with confirmed DDSP. They report that injecting the soft palate with genipin resulted in a reduction of snoring loudness in all horses with DDSP and elimination of DDSP in at least one of three horses.

The authors suggest that genipin crosslinking could become an effective and safe treatment for soft palate related breathing abnormalities.

For more details, see:

Soft Palate Modification Using a Collagen Crosslinking Reagent for Equine Dorsal Displacement of the Soft Palate and Other Upper Airway Breathing Disorders.

Hunt S, Kuo J, Aristizabal FA, Brown M, Patwardhan A, Hedman T.

Int J Biomater. (2019) Apr 1;2019:9310890.

doi:10.1155/2019/9310890