It is not easy to show in full details the changes in wool production during the growing of lambs, mainly because the period of the year in which ewes will be lambing is mostly restricted to spring, consequently it will be difficult to separate seasonal rhythm from the original pattern of wool growth.
In order to solve the problem the authors took twenty-seven lambs produced outside the normal lambing season from 1957 to 1960. And these twenty-one lambs together with eight lambs produced under normal condition were reared from birth to the twelfth month for female and from birth to sixth month for male, during the years 1957-1963 in order to investigate analytically the growth pattern and environmental effects.
In sequence to the previous paper the authors report here now on wool growth and seasonal effects during the growing of lambs.
Rapid increasing rates of number of fibre follicles on surface skin were observed within birth to the 3rd month in spring lambs, summer lambs and winter lambs; within birth to the 4th month in autumn lambs; and within the 4th to the 6th months in early -summer lambs. It was recognized that the most rapidly increasing periods were under early spring and autumn conditions. Wool density in winter lambs increased from birth to the 1st month differing from tendencies in other groups and the fact which Mimura has reported the progressive decreasing along the growing of lambs. On the variation, in general, of average fibre diameter increasing size from birth to the 3rd or the 4th months and declining tendencies from the 4th month to the 6th month were noticed. Especially poor sizes were remarkable in early-summer lambs within the 4th to the 6th months under autumn condition and in winter lambs within the 9th to the 12th months under winter condition. Therefore, the authors suggest that decline in fibre diameter may be attributed to day-shortness and poor nutrition rather than cold temperature under autumn and winter condition.
It is very important to suggest that all components affecting wool production are increasing phases, in exception with wool density, during early stage after birth responsing to the rapid growth and development of lambs.
In all groups the highest clean wool production per unit area occurred within the 3rd to the 4th months. Although the highest production in autumn lambs was synthetically attributed to the high growth rates in skin expansion, fibre diameter and fibre length within the ages, those in other groups might be attributed not only to one or two components which could be interaction of various components upon each other.