Effects of melatonin administration to cashmere goats on cashmere production and hair follicle characteristics in two consecutive cashmere growth cycles

Abstract Background: Short-term melatonin treatment of cashmere goats has been shown to increase the quantity and quality of cashmere fibre. However, the long-term effects of melatonin treatment on cashmere production and hair follicle characteristics of these goats has not been reported. Therefore, we investigated changes in cashmere production and in hair follicle populations and their activity in melatonin-treated cashmere goats for two consecutive cashmere growth cycles.Methods: Twenty-four female Inner Mongolian Cashmere goats were randomly allocated to two groups (n = 12), one of which received melatonin implants, the other being an untreated control group. Melatonin implants were subcutaneously inserted behind the ear at a dose of 2 mg/kg live weight on two occasions – 30 April and 30 June 2016. Cashmere samples were collected at combing in April of 2017 and 2018. Blood and skin samples were collected monthly between April and September 2016, and during April and September in 2017. Results: Our results showed that melatonin treatment of cashmere goats in one cashmere growth cycle increased (P < 0.05) weight, length, density and decreased (P < 0.01) diameter of cashmere fibre, however it did not affect cashmere production in the following annual cycle. Melatonin treatment of cashmere goats had no effect on the population of secondary hair follicles for the two consecutive cycles. However, in the first growth cycle following treatment it advanced (P < 0.05) the onset of activity of secondary hair follicles by 2 months and it increased (P < 0.05) the population of these follicles that were active. Serum melatonin concentrations of the treated goats were elevated, relative to those of the control group (P < 0.05), but only during the first growth cycle.Conclusions: In summary, melatonin treatment of cashmere goats in one cashmere growth cycle improved cashmere production for that cycle only, with no residual effects on the following cycle. This makes the technique acceptable to the cashmere goat industry. The improvement in cashmere production following treatment of goats with melatonin appears to involve an acceleration of the annual regeneration of secondary hair follicles and an increased population of active secondary hair follicles in the skin of cashmere goats.