Seasonal fleece changes in two selection lines of Scottish Blackface sheep during their lifetime on the hill

Abstract

SUMMARYTen Scottish Blackface ewes from each of three lines, a line selected for hairiness, a line selected for a fine fleece, and an unselected control, were fleece and skin sampled in April, June, September and December, during their 6J year life-span on the hill.Fleece weight differed between individuals and between lines, and declined by 4% per year from 1·5 kg at 1 year, to 1·3 kg at 6 years. Fleece grade was inadequate as a method of denning fleece differences between the lines.The height of the spring ‘rise’ in growth in April differed between years, and between lines, declining 2 mm a year from 26 mm at 1 year. Staple length was greatest in the Hairy group and least in the Fine group (P < 0·05). Growth in length was faster between September and December (autumn) than between April and June (spring). Staple length decreased by 14 mm a year.The lines differed significantly (P < 0·05) in mean fibre diameter but not in modal fibre diameter. There was a highly significant decrease in diameter from summer to winter, ranging from 20% in the Fine line to 31% in the Hairy line, the greater decrease in the Hairy line being attributed to loss of medulla.The selection had between 1954 and 1972 changed the S/P follicle ratio of 3·0 in the control to 2·8 in the Hairy line and 3·2 in the Fine line. Most seasonal follicle inactivity occurred in April, December came second, and June invariably had more follicle inactivity than September. The control line had the greatest values of primary follicle inactivity and the Fine least. Among the secondary follicles the Hairy line had most inactivity, and the control line least. Maximum primary fibre medullation occurred in either June or September, and medullation was at a minimum in December or April.