The effects of exogenous melatonin on wool quality and thyroid function in Rasa Aragonesa ewes

The effect of melatonin on wool quality and thyroid function was studied. Ten ewes received a melatonin implant (M) on March 2004, and 10 ewes which were not implanted served as control (C). At monthly intervals over 12 months, f ibre length and growth were calculated, and plasma thyroxine (T4) concentrations were measured. Wool samples (~N = 2000 fibres) were collected and fibre diameter, standard deviation and coefficient of variation of fibre diameter, spin fineness, comfort factor, 5% of fibres «x» μm above the mean diameter, curve, and clean yield were measured. In summer, M ewes had significantly lower plasma T4 concentrations than C ewes, with significant group (P < 0.05) and season (P < 0.01) effects. Melatonin ewes produced shorter wool than C ewes (P < 0.001) and, in autumn, the differences were statistically significant. Fibre growth did not differ significantly between groups. Throughout the year, M ewes produced wool with a fibre diameter (mean = 26.5 ± 0.2 μm) that was significantly (P < 0.01) shorter than C wool (means = 27.2 ± 0.5 μm). Overall, the melatonin treatment had a significant (P < 0.01) effect on mean comfort factor, and the differences between groups were significant (P < 0.05) in summer and autumn. The overall annual mean curve value of wool produced by M ewes (80.9 ± 1.7) was significantly (P < 0.01) lower than wool produced by C ewes (82.8 ± 1.3) and, in winter, the difference between groups was significant (P < 0.05). In conclusion, exogenous melatonin in spring positively affected mediumand long-term measures of wool quality. The physiological processes mediating these mechanisms remain to be elucidated. Additional key words: fibre diameter, thyroxin, wool growth.