Abstract
Background:
Equine Gastric Ulcer Syndrome (EGUS) is the most common disease affecting the equine stomach. Heart rate variability (HRV) describes and quantifies the variability between consecutive heartbeats due to the neurohormonal regulation of the heart. It has been considered a non-invasive method to detect autonomic tone changes that can be influenced by pain and disease.

Aim:
This study aimed to assess the HRV indices in horses affected by EGUS submitted or not to treatment.

Methods:
A cohort of 45 mares underwent baseline gastroscopy (T0); 24/45 mares diagnosed with Equine Squamous Gastric Disease (ESGD) graded 2 out of 4 or greater were included and assigned to treated (T, n=12) or non-treated (NT, n=12) groups. The T group received omeprazole and sucralfate for 28 days. Heart rate (HR) was recorded using an HR monitor before the treatment (T0) and at the end of the treatment (T29). R-R intervals were analysed using commercial software to obtain time-domain, frequency-domain, and geometric indices for the HRV parameters. Gastroscopies were performed at the end of the treatment (T29) for both groups and at T14 for the NT group.

Results:
At T0, ESGD at least 2/4 score was diagnosed in all the horses included, while Equine Glandular Gastric Disease (EGGD) at least 1/4 score was diagnosed in 8/12 and 12/12 horses in the NT and T group, respectively. No significant differences were observed in HRV indices within or between groups over time. The treatment significantly reduced ESGD scores (p=0.018), but not the EGGD scores (p=0.573) in the T group.

Conclusion:
Although HRV did not change significantly post-treatment, it appears to be a promising tool for assessing autonomic function in EGUS.

Key words: Equine; Equine glandular gastric disease; Equine squamous gastric disease; Heart rate variability; Ulcers.