Abstract
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.
