Seasonal variation in the mitotic activity of secondary fibre follicles in adult cashmere goats

Abstract

Seasonal variation in secondary follicle activity was studied in the skin of eight adult (five female, three male) cashmere goats living in a Mediterranean climate (35°S, 138.5°E). From 17 consecutive monthly skin biopsy and fibre samples, it was determined that secondary follicle activity, and therefore the actual cashmere growing season, occurred over a period of 10–11 months, follicles becoming inactive in late June (mid-winter). Mitotic activity was low in spring when the new season's growth was beginning, and in autumn, immediately before the dormant period. Activity gradually increased through spring to early summer when it reached a maximum, followed by a sudden drop in late summer. Activity then increased once more in autumn before falling to zero in winter. The general pattern of mitotic activity was not very different between males and females except in spring when males tended to be in advance of females and proceeded at a faster rate. Males also showed a tendency to retain the old coat after the new one had started to grow and thus had significantly more cashmere fibre in their coat during spring and early summer than did females. Fibre diameter was narrowest from spring to early summer and broadest in autumn. This histological study enabled a more detailed examination of the cashmere growing season than is possible from fibre samples alone, and it is suggested that an increase in daylength following the shortest day on June 22 stimulates renewed activity of the secondary follicles.