In order to elucidate the cause of the active gizzard movement of chick fed with grit, the effects of grit feeding on the development of chick gizzard and the myofibril content of the gizzard muscle were studied.
After feeding two groups of 50 male broiler day-old chicks, one group with and another without grit, for 8 weeks, the birds were killed and their gizzard removed for examination.
1) An improvement was hardly observed on the body weight gain and the feed efficiency with grit feeding.
2) The development of gizzard was largely improved with grit feeding. The fresh muscle weight, mucosa weight, size and muscle total N content of the gizzard from chicks fed with grit were all larger than those from chicks fed without grit.
3) The percentage of myofibrillar N in the total N content of the gizzard muscle from chicks fed with grit was 35.8% at 8 weeks old, whereas that from chicks fed without grit was 34.9%. Although the difference was not significant between these two values, absolute content of myofibrillar N should be largely increased with grit feeding, since the total N content of the gizzard muscle from chicks fed with grit was remarkably large compared with those from chicks fed without grit.
As the contractile tension of a muscle is thought to be directly related to the myofibril content of muscle fibers, the increased myofibril content with grit feeding must be considered as a cause of active gizzard movement.