Skin deiodinase profiles and associated patterns of hair follicle activity in cashmere goats of contrasting genotypes

The roles of skin deiodinase enzymes in the expression of genotypic differences in hair follicle activity and cashmere fibre growth and moult were studied in 9 Siberian (S) and 10 Scottish cashmere (SC) goats. The proportion of animals exhibiting cashmere growth was significantly greater in S than in SC goats in both late July (P<0.001; early in the season of growth) and between January and April (P<0.001; late in the season of growth), but there was no significant difference in the time of moult onset. Patterns of hair follicle activity exhibited similar seasonal differences, with secondary follicle activity being higher in S than in SC animals during the January-June period. Overall mean concentrations of IGF-I were lower (P<0.01) in S than in SC animals and mean T-4 concentrations were higher (P<0.05) in S than in SC animals, but these differences were not related to genotypic differences in follicle activity or cashmere fibre growth. Mean concentrations of insulin, prolactin, and T-3 did not differ with genotype. Between January and early April, mean prolactin concentrations were higher in S than in SC animals (P<0.05). Monodeiodinase type II (MDII) activity in skin samples was highest (P<0.001) during December and January (short day photoperiod) and was lower in S than in SC animals (P<0.05) at these times. Mean monodeiodinase type III (MDIII) activity was highest during June and July (long day photoperiod). There was no difference between genotypes in the overall mean levels of deiodinase activity but, during January-March, when prolactin concentrations were higher in S than in SC goats, there was a higher rate of follicle activity and fibre growth in S goats. It is postulated that individual and genotype differences in hair follicle activity and cashmere growth are partially dependent on the pattern of expression of deiodinase enzymes in the skin. However, the actions of each enzyme are likely to depend on, among other factors, the absolute levels of expression of each type, the ratio of MDIII to MDII, the physiological state of the follicle, and the associated hormone profiles.