Fleece growth in Australian cashmere goats. IV. The role of prolactin in the initiation and cessation of cashmere growth

Abstract

An experiment was designed to investigate the effect of prolactin (Prl) on the initiation and maintenance of cashmere growth. Intra-muscular injections of bromocryptine (0.5 mg/kg) three times per week were used to suppress Prl secretion from August to December or from January to June in two groups of three male and three female goats. Bromocryptine effectively suppressed Prl concentrations to below 10 ng/mL for the duration of the treatments. Initiation of cashmere growth goats injected in July to December occurred in January after high post-treatment levels of Prl began to decline. Cashmere growth of male control goats was considered unrepresentative of normal cashmere growth, but initiation in female control goats occurred in December. Bromocryptine treatment from January to June had no effect on active cashmere growth. but inhibited cashmere growth not already initiated. Bromocryptine injections had no effect on serum T4 concentrations. The results are discussed in relation to the role of Prl in the initiation, maintenance and cessation of cashmere growth. It was concluded that either natural or induced peaks of Prl concentrations were associated with the initiation (falling concentrations) and possibly also with the cessation of cashmere growth (rising concentrations).