Effects of Grazing Muzzles on Intakes of Dry Matter and Water-Soluble Carbohydrates by Ponies Grazing Spring, Summer, and Autumn Swards, as well as Autumn Swards of Different Heights

Abstract

Dry matter (DM) and water-soluble carbohydrate (WSC) intakes (DMI and WSCI, respectively) were determined in four mature ponies, grazing spring, summer, and autumn pastures on four, 3-hour occasions per pony per season when fitted with or without a grazing muzzle. Pasture intakes were determined by change in liveweight (LW) over the 3-hour grazing period, after accounting for insensible weight loss and weight of excreta. Daily pasture samples were analyzed for DM and WSC. The effect of sward height on herbage intake characteristics by muzzled or unmuzzled ponies allowed 10 single bites of short (ca. 7 to 10 cm), medium (ca. 20 cm), and long (ca. 40 cm) swards was also investigated. Grazing muzzles significantly (P < .01) reduced pasture DMI by 77, 77, and 83% for spring, summer, and autumn pastures, respectively. During at least one 3 hour grazing session across the seasons, the DMI of each pony when not muzzled exceeded 1% of LW. Water-soluble carbohydrate intakes (g WSCI/100 kg LW/3 hours) were significantly lower (P < .05) across seasons when ponies were muzzled versus unmuzzled. When unmuzzled, ponies' WSCI from summer swards were significantly (P < .05) lower than from autumn swards. Seasonal differences in WSCI by muzzled ponies were not significant. When unmuzzled ponies grazed swards of different heights, the first bite generally reduced sward length by approximately half. However, when muzzled, first bites of swards resulted in highly variable reductions in sward length. Ponies appeared to experience greater difficulty in accessing the longer versus the shorter swards via their grazing muzzles.