Fleece growth in Australian cashmere goats. III. The seasonal patterns of cashmere and hair growth, and association with growth hormone, prolactin and thyroxine in blood

Abstract

The seasonal patterns of cashmere and hair growth, and prolactin, thyroxine and growth hormone concentration in blood were investigated in male, female and castrated male 6- month-old Australian cashmere goats for 27 months. Seasonal patterns of cashmere growth were distinct with length increasing from a minimum in December to maximum (50-60 mm) in July. Initiation of cashmere growth in female goats was consistently earlier than that of males, with that of castrates being similar, later and earlier than males in 1987, 1988 and 1989 respectively. The initiation of cashmere growth progressed in a wave from the hip to the shoulder (6 weeks). There were no significant effects of sex on maximum length of cashmere grown. Prolactin secretion was also seasonal, increasing from minimum values in July-August (20 ng/mL) to peak levels around December (50-350 ng/mL). Thyroxine concentrations were higher in summer than winter, but seasonal changes were not as distinct as those of prolactin. Growth hormone secretion was aseasonal, and declined with age. It has been proposed that peak levels of prolactin in December were associated with the initiation of cashmere growth, with active growth occurring as levels declined. Neither thyroxine nor growth hormone appear to have a regulatory influence on the cashmere growth cycle.