Effects of rectal examination on intraocular pressure and behavioral responses in pregnant and non-pregnant mares.

BACKGROUND

Rectal examination is routine in equine reproduction but may trigger acute stress affecting welfare and safety. Intraocular pressure (IOP) responds rapidly to autonomic changes and may capture short-lived stress responses.

AIMS/

OBJECTIVES

To evaluate whether rectal examination acutely affects IOP and behavioral responses in mares, and whether reactions differ by reproductive status.

METHODS

Twenty Rahvan mares (10 pregnant, 30-40 days' gestation; 10 non-pregnant; 4-7 years) underwent transrectal examination without sedation. IOP was measured bilaterally at six time points: 2 min pre-exam (T1), during (T2), and 1, 5, 10, 15 min post-exam (T3-T6) using rebound tonometry. Behavior at T2 was scored 1-5. Linear mixed-effects models analyzed IOP; ordinal mixed models analyzed behavior. ΔIOP (T2-T1) correlation with behavior was assessed via Spearman's ρ.

RESULTS

Pregnant mares showed higher behavioral resistance than non-pregnant mares (median 4 [IQR 3-4] vs 2 [2-3]; OR = 3.8, 95% CI 1.6-9.2; p = 0.003). IOP rose during examination in both groups, more in pregnant mares (mean increase from baseline +4.2 mmHg) than in non-pregnant mares (+1.3 mmHg), resulting in higher IOP at T2 (34.8 ± 2.1 vs 31.6 ± 1.7 mmHg; p < 0.001), remained higher at T3, and returned to baseline by T4-T6. ΔIOP correlated positively with behavioral score (Spearman's ρ = 0.62; p = 0.004). Area under the IOP-time curve did not differ (p = 0.348).

CONCLUSION

Rectal examination elicited transient IOP elevations and behavioral resistance, more pronounced in pregnant mares. IOP is a rapid, sensitive adjunct for welfare assessment, emphasizing handling during reproductive procedures.