روح اله میر محمودی

Ten female and 10 male Merghoz goats with initial liveweights of 24.02 ± 1.7 and 29.2 ± 1.2 kg (mean ± s.e.) respectively were used to investigate the effect of naturally changes in photoperiod on hair follicle activity and fibre growth in a 365 day study. The animals were housed in individual pens, under natural day length condition at west of Iran, Kermanshah (34◦18N and 47◦3E and 1420 m above sea level). A diet was offered with an estimated concentration of metabolizable energy and crude protein of 7.9 MJ and 98.8 g/kg DM respectively. Follicular density (FD), percentage of active primary and secondary follicles (PAP and PAS) and ratio of secondary to primary follicles (S/P) were determined from skin biopsies, taken from the right mid-side of the goats every one month. Clean fibre yield and fibre diameter were measured from mid-side patches harvested at the end of every month after morning feeding. Dry matter intake (DMI) and average daily gain (ADG) displayed a substantial seasonal variation. There was a significant effect (p < 0.001) of season on PAP and PAS (primary: 98.0, 74.1, 45.9 and 89.0%; secondary: 99.0, 80.9, 70.6 and 92.5%; for summer, autumn, winter and spring, respectively) but, no seasonal differences were observed in FD and S/P. Seasonal differences in clean fibre yield and fibre diameter patterned those of follicle activity. There was a season × sex interaction on both fibre growth rate and fibre diameter. It is concluded that seasonal cycles of feed intake, growth, hair follicle activity and fibre growth may occur in goats.