The purpose of present study was to clarify the effects of weaning conditions on the morophological and functional development of the jaw and muscle of guinea pigs.
Fifty hartley guinea pigs were used.3 days after birth they were divided into four groups as follows.
1) Control group: They were feed under normal conditions throughout the weaning period (breast feeded by their dam and solid-type food).
2) Solid-type food group: They were feed with solid-type food (RC-4® Oriental Kobo Co. ).
3) Soft-type food group They were feed with powdered RC-4®food.
4) Milk food group: They were feed with milk (Eva milk®, Nessle Co. ).
Experiment 1: Ten guinea pigs of each group were sacrificed by ether inhalation 40 days after birth. The masseter and digastric muscles were entirely removed surgically and then the wet weights were measured. For craniometric analysis, dry skull specimens were then prepared and measurements of the reference points were made. As a result, it was shown that the weight of both the masseter and digastric muscles of solid-type food group was heavier than those of soft-type food and milk food groups. The lower jaw of solid-type food group was bigger than that of soft-type and milk food groups, while with the upper jaw, there was no significant difference between the solid-type and soft type food group.
Experiment 2: From 17 days after birth, EMG of the masseter of the groups with solid-type and soft-type food were recorded with the guinea pigs eating by will with an interval of 5 days. The EMG of the masseter of soft-type food group showed no changes even as time passed, and showed a pattern similar to the drinking behavior. With the solid-type food group, regularity of the chewing rhythm and prolonged duration was noticed.
It was concluded that the weaning conditions may affect the development of jaw and muscles in guinea pigs.