Effect of melatonin treatment in spring and feed intake on wool growth andthyroxine secretion in Rasa Aragonesa ewes

A total of 20 entire and 10 ovariectomized (OVX) oestradiol-implanted ewes were used to study the effect of exogenous melatonin and plane of nutrition on wool growth and thyroxine (T-4) secretion, On 21 March, entire animals were divided into two groups and fed 1.5 x energy requirements for live wei ght maintenance (M) (H, n = 10) or 0.5 x M (L, n = 10). A subcutaneous impl ant containing 18 mg of melatonin was implanted in the base of the ear of h alf of the animals of each group (M), while the remainder had no implant (C ). Ali OVX ewes received a melatonin implant and were fed a live weight mai ntenance diet. Wool growth and plasma T4 Concentrations were recorded at 2- weekly intervals. At the end of the experiment (30 May), no differences bet ween groups for wool growth were detected (HM: 25 +/- 1.2; HC: 21 +/- 1.7; LM: 23 +/- 1.7; LC: 21 +/- 0.7: OVX: 22 +/- 10.8 mm), although L animals pr esented the lowest mean plasma T4 concentrations in comparison with H (P < 0.01) and OVX (P < 0.05) groups (HM: 46 +/- 3.9; HC: 51 +/- 3.8; LM: 32 +/- 3.1, LC: 35 +/- 4.6; OVX: 43 +/- 2.9 ng/ml), In conclusion, and after 2 mo nths, wool growth has not been modified either by melatonin treatment or le vel of nutrition, although undernutrition induced a significant reduction o f circulating T4 profiles. The use of melatonin to control sexual activity in sheep should not be an obstacle for wool production. (C) 2001 Elsevier S cience BN. All rights reserved.