Seasonal variation of fibre follicle activity and wool growth in fat-tailed Sanjabi sheep in west Iran.

This experiment was conducted to investigate the seasonal pattern of hair follicle activity, wool growth and fibre diameter (FD) in Sanjabi sheep in west Iran, Kermanshah (34° 18' N and 47° 3' E, elevation 1420 m). Ten male and 10 female Sanjabi sheep with an initial live weight of 32.1 ± 1.3 and 32.7 ± 1.5 (means ± SD), respectively, were used in a 365-day study. A diet was offered with an estimated concentration of 2.18 Mcal metabolizable energy and 130.0 g/kg DM crude protein. Body weight, average daily gain (ADG) and dry matter intake (DMI) were recorded weekly. The percentages of active primary and secondary wool follicles (PAP and PAS), follicle density and the ratio of secondary to primary follicles (S/P) were determined from skin biopsies, taken from the right mid-side of the sheep at monthly intervals. Raw and clean fibre growth rates and FD were measured from left mid-side patches (10 × 10 cm) harvested at the end of every month. There was a gradual increase in live weight throughout the experiment, while ADG and DMI changed in concert with day length. The greatest values for PAP and PAS were observed in summer, whereas lowest were obtained in winter (p < 0.001). Clean wool growth rate and FD were greatest (p < 0.001) in summer and lowest (p < 0.001) in winter. It is concluded that a seasonal cycle of feed intake, body growth, fibre follicle activity, wool growth and FD occur in fat-tailed Sanjabi sheep.