EFFECT OF MUZZLING ON RUMINATION IN SHEEP

Abstract

Two experiments were completed using four esophageal-fistulated sheep (two per experiment) to study the breakdown of rumen particles of grass hay (bromegrass or reed canarygrass) when rumination was either allowed to occur normally or was restricted by means of a muzzle. When the sheep were muzzled during the nonfeeding portion of the day, there was a distinct limitation of voluntary hay intake. Muzzled sheep chewed more often than unmuzzled sheep (P < 0.01) during eating and, presumably as a result, the particles in their mastication boluses were smaller (P < 0.05). During rumination the regurgitated and chewed boluses from sheep that had been muzzled were larger (P < 0.05) than those from unmuzzled sheep. The proportion of large particles (LP, particles retained on a 1.00-mm screen) of the regurgitated bolus, rumen contents and feces were greater (P > 0.05) for muzzled than unmuzzled sheep. The effectiveness of breakdown of LP retained for chewing during the rumination cycle increased (P < 0.005) with time after feeding (33% at 3 h postfeeding for bromegrass; 57% at 11 h postfeeding). This increase was eliminated by muzzling. The specific fragility (LP breakdown per chew per unit of LP in mouth) of particles from unmuzzled sheep was consistently greater (P > 0.05) than that of particles from muzzled animals. Muzzling markedly reduced the extent to which specific fragility increased with time after feeding and increased (P > 0.01) rumen fluid retention time from 7.4 to 17.4 h. The rumen input-output balance for hay particles was estimated. It is concluded that rumination is the major factor in decreasing the size of forage particles in the rumen, thereby exposing greater surface area to microbial attack and facilitating passage along the intestinal tract. Key words: Sheep, rumination, muzzle, particle breakdown, specific fragility, rumen retention time