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

Abstract

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, fibre 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" micro m 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 micro m) that was significantly (P<0.01) shorter than C wool (means = 27.2 +/- 0.5 micro m). 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 medium- and long-term measures of wool quality. The physiological processes mediating these mechanisms remain to be elucidated.