Effect of Restricted Grazing on Hindgut pH and Fluid Balance

Horse owners utilize many management practices to limit calorie intake for obese horses, including restricting pasture access via a grazing muzzle. However, research has shown that horses often increase pasture intake when returned to an unrestricted situation. Drastic changes in grain intake are known to cause digestive upsets, particularly in the hindgut, so researchers set out to determine if drastic changes in pasture intake yielded similar results.

The research team, led by Paul D. Siciliano, PhD, associate professor in the North Carolina State University Department of Animal Science, separated six mature light horse geldings of similar weight and body condition into two groups.

A control group had access to pasture continuously while a restricted group wore a grazing muzzle for 12 hours per day. After seven days, the groups switched protocol for an additional seven days. On day seven of each period, blood and feces were collected at intervals for plasma protein and fecal pH determination. In addition, pasture samples were obtained for chemical composition analysis.

After reviewing their results, the team found that hindgut health in horses with restricted access to pasture by grazing muzzle for 12 hours per day was not compromised compared to horses with unrestricted access to pasture.

Additionally, the team reported no significant difference in fecal pH--an indicator of hindgut fermentation, influenced by dietary composition--between the control and restricted horses in this study.

Another study finding involved blood plasma protein volume, which serves as a measure of hindgut fluid balance. Reduced feed intake, including roughage or pasture, can result in reduced water intake, increasing plasma protein volume. An increased feed intake following restriction can increase digestive secretions, thus, decrease plasma protein volume.

In this study, Siciliano found that plasma protein volume was not affected by treatment group, which suggests that fluid balance was not altered by treatment. Fecal dry matter percentage was no different between groups, further supporting that fluid balance was not altered by restricting pasture intake.

The team ultimately concluded that restricting pasture access does not appear to have negative effects on hindgut fermentation or fluid balance.

The study, "Effect of Restricted Grazing on Hindgut pH and Fluid Balance," appeared in September in the Journal of Equine Veterinary Science. The abstract is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.