Investigation of the effect of pasture and stable management on large intestinal motility in the horse, measured using transcutaneous ultrasonography.

Reason for performing study: Management regimes have been identified as risk factors for equine intestinal motility disorders. However, it is not known how management factors affect gastrointestinal motility.

Hypothesis: Large intestinal motility was similar in horses on a stabled and a pastured management regime.

Objective: To investigate the effect of 2 different management regimes on large intestinal motility assessed with ultrasonography.

Methods: A within-subjects crossover design was used to compare large intestinal motility between a stabled and a pastured regime in 16 working horses. Group A was managed under a standardised stabled regime throughout the study. Group B was maintained at pasture for the first monitoring phase and then transferred to the stabled regime for the second monitoring phase. Motility of the caecum, sternal flexure and aboral left ventral colon (contractions/min) was measured twice daily for 2 consecutive days using transcutaneous ultrasonography. Mean values for each management regime were pooled for analysis using multilevel statistical modelling.

Results: Significant variables identified by the model included: time of day, region of intestine, management regime, and combination of region of intestine and management regime. Motility assessed by ultrasound was significantly lower in stabled horses compared to pasture-kept horses. Intestinal motility for caecum was 1.7 ± 0.3 contractions/min (pastured = 2.0, stabled = 1.4), sternal flexure was 1.6 ± 0.2 contractions/min (mean (pastured = 1.7, stabled = 1.5), and left ventral colon was 0.8 ± 0.3 contractions/min (pastured = 1.0, stabled = 0.7).

Conclusions: The null hypothesis was disproven. Large intestinal motility assessed by ultrasound was significantly reduced in stabled horses compared to pastured horses. This effect was most marked in the aboral left ventral colon.

Potential relevance: This study has demonstrated a possible mechanism for the increased risk of large intestinal impactions in stabled horses.