Endocrine control and manipulation of hair follicle activity in the cashmere goat

The cashmere goat has an annual cycle of hair growth and moulting, which is associated with changes in photoperiod.The first experiment was designed to determine if slow release melatonin implants could be used to delay the spring moult and initiation of hair folicle activity, as has been reported in mink and Blue- foxes, and to investigate other endocrine changes associated with the onset of the moulting period. Adult and juvenile cashmere goats were implanted with melatonin from mid -December until May. The adult goats became photorefractory to the continuous release of melatonin, and exhibited advances in the onset of moulting and the seasonal rise in plasma prolactin concentration, when compared to the control animals. The juveniles did not differ from the controls in any of the parameters measured. The data were not consistent with the hypothesis that melatonin implants could be used to delay the spring moult and reactivation of the hair follicles in the cashmere goat.Another group of goats was treated with melatonin implants in April. They demonstrated a significant depression in plasma prolactin concentration compared to the controls.In the second experiment the asociation between the increase in plasma prolactin concentration and the onset of moulting and hair follicle activity was investigated. Prior to the experiment a dose response study of the dopamine - agonist bromocriptine was conducted to establish the dose of bromocriptine required to suppress plasma prolactin concentration to base -line levels for 14 days. Groups of adult female goats were treated with either exogenous ovine - prolactin, bromocriptine or a combination of both treatments. The moult and hair follicle activity were advanced in the prolactin and bromocriptine -plusprolactin treated groups and delayed in the bromocriptine- treated group, compared to the controls. This conclusivley demonstrated that a rise in plasma prolactin concentration was necessary for the initiation of the moult and hair follicle activity.The final experiment was designed to determine whether a period of plasma prolactin suppression followed by a rapid increase in plasma prolactin concentration would accelerate the moult and thereby synchronise the onset of moulting within a group of animals. Groups of animals were treated with either bromocriptine, bromocriptine followed by bromocriptine plus prolactin or bromocriptine followed the administration of 'Sulpiride' (a dopamine antagonist and more readily available than prolactin). Consistent with the previous study the onset of moulting was delayed until the end of the period of prolactin suppression. The moult occured rapidly after plasma prolactin elevation and the asynchrony within the groups was reduced slightly compared to the controls.It is concluded that the timing of the spring moult in the cashmere goat can be altered by manipulating plasma prolactin concentrations. Factors other than prolactin may, however, be involved at the follicular level and controlling the response of individual follicles