The role of prolactin in the reactivation of hair follicles in relation to moulting in cashmere goats

Abstract

The effects of the suppression or elevation of plasma prolactin concentrations in spring on the timing of the reactivation of the hair follicles and the timing of the spring moult were investigated in cashmere goats. Thirty eight adult female goats, housed under conditions of natural photoperiod at 55 degrees 55'N from mid-December until May, were allocated to four groups starting on 5 January: ten served as untreated controls, eight received 2 mg ovine prolactin subcutaneously every 12 h for 7 weeks (PRL), twelve received 35 mg bromocriptine intramuscularly every 14 days for 17 weeks (BCR) and eight received injections of both ovine prolactin and bromocriptine at the above dose rates for 7 weeks (PRL+BCR). In the PRL group there was an earlier reactivation of the secondary hair follicles (PRL vs control, proportion of secondary follicles in antigen, weeks 1-5, P < 0.01) associated with an earlier moult of secondary fibres (cashmere) but no significant difference in the activity of the primary hair follicles. In the BCR group there was a delay in the reactivation of both the secondary and primary hair follicles (BCR vs control, proportion of secondary and primary hair follicles in anagen, weeks 5-13, P < 0.01) and a delay in the moult. In the PRL+BCR group there was an early reactivation and moult similar to the PRL group. Voluntary food intake (VFI) and liveweight were also measured. Only in the BCR group was there a decrease in VFI compared with the controls but with no effect on liveweight.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of prolactin receptor expression in ovine skin in relation to circulating prolactin and wool follicle growth status

“…Earlier studies showed that changes in circulating prolactin can trigger hair cycle progression (Pearson et al 1993, Dicks et al 1994, but it has been unclear how this hormone can exert apparently opposite influences at different phases of the cycle. The close association between the level of PRLR mRNA in the skin and follicle growth status suggests that cellular activity in the follicle is related to receptor abundance and the consequent level of signalling.…”

Short communication: Melatonin implantation during the non-growing period of cashmere increases the cashmere yield of female Inner Mongolian cashmere goats by increasing fiber length and density

“…Cashmere growth exhibits a seasonal rhythm (Dicks et al, 1994;Klören & Norton, 1995;Santiago-Moreno et al, 2004). Research has shown that melatonin is a critical intermediary between photoperiod and cashmere growth with circulating melatonin levels directly affecting cashmere growth (Teh et al, 1991;Klören & Norton, 1995).…”

Melatonin and cashmere growth in Inner Mongolian cashmere goats

“…Seasonal cashmere growth cycles in Inner Mongolian cashmere goats have been well defined with outgrowth on the surface in August and ceases in following February with shedding of the fleece at the end of April, and the nongrowing period for cashmere is from March to July (Da et al 1991). Cashmere growth exhibits a seasonal rhythm arising from circannual changes in the natural photoperiod (Klören and Norton 1993;Dicks et al 1994;Santiago-Moreno et al 2004). Melatonin is a critical intermediary between the photoperiod and cashmere growth (Teh et al 1991).…”