Cyclical fleece growth in cashmere goats

Abstract

Seasonal changes in fleece parameters were studied in mature feral doe goats, known to produce commercial quantities of cashmere and housed in natural light (NL) or continuous light (CL).Circannual changes in volume growth rate (VGR) of cashmere in NL were asynchronous with those of hair, resulting in maxima in April and November respectively, indicating that follicle-specific mechanisms are controlling the rate of follicle activities.Cycles of cumulative length of cashmere and hair in NL were synchronous. Cashmere maxima of 64.0 and 62.3 mm occurred in June and July respectively for two consecutive years. Distinct circannual cycles of linear growth (period, 365 days) were evident. While exposure to CL initially reduced the cycle period, after 2 years an extended cycle period emerged; this may have been due to photodesensitization.In NL, cashmere fibre diameter minima occurred at June-July and February each year. Hair fibres underwent only one cycle of diameter change each year. The period of the cycles was reduced by CL.An annual cycle of cashmere brush end fibre formation was apparent in NL. This cycle was associated with the cessation of growth in June-July, and a subsidiary event occurred between December and March. Continuous light accelerated brush end formation.Cyclic fibre shedding produced a circannual rhythm in fleece composition with maximum cashmere: hair ratio (CHR) in April-May in non-breeding goats. The maximum CHR of 5.9: 1 in NL did not reach its potential, as illustrated by the follicle S:P ratio of 6.9:1 in the skin. This suggests an irreversible loss of cashmere fibres from the fleece following the cycle of brush end formation in February.The maximum mean length of cashmere and time of occurrence were similar in grazing and penned does, although grazing does were only sampled in 4 months of one year.