Influence of feed form on gizzard morphology and particle size spectra of duodenal digesta in broiler chickens

We examined gizzard morphology and diet particle size reduction in broiler chickens fed a wheat-based diet that was offered in either a mash or a pelleted form. The pelleted diet had a lower proportion of coarse particles on wet sieving. Birds fed the mash diet had a significantly larger gizzard mass per unit body mass. The gizzards of all birds increased uniformly in size, there being no significant change either in the ratio of content to empty mass or in the ratio of gizzard length to breadth with diet. Thus, there was no tendency for coarse particles to accumulate in the gizzards of bird fed the mash diet. The relative proportion of all classes of particles below 0.500mm was increased and the relative proportion of all particle classes above 0.500mm was reduced in birds regardless of feed form. The relative increase of particles in all classes below 0.500mm was greater in birds fed mash feed. However, digesta exiting the gizzard of birds fed mash diet contained significantly greater amounts of particles of size classes 1mm and greater than digesta of those fed the pelleted diet. Thus, whilst the gizzard operates to generally reduce particle sizes above 0.500mm and increase those below this size, this reduction is not uniform and likely to be a probabilistic function as it is in the human mouth.