The use of skin autografts to study wool growth cycles in sheep

Abstract

The aim was to produce regions in which the wool growth cycle was out of phase with that in the surrounding skin. Four experiments were carried out involving 60 full-thickness autografts on the flanks of Wiltshire and Soay sheep. In two experiments skin was stored at 70°C for six months from summer to winter, and vice versa, but whatever the season, and whether the graft had been stored or replaced immediately as a control, wool growth on the graft was the same in each ease. In two other experiments, grafts made in autumn grew wool during the winter when the surrounding follicles were mostly inactive. The wool grew for at least the usual six months, after which some of the fibres shed, as in a normal autumn moult. In other animals growth continued for about a year, when the graft wool was considerably longer than that of the surround. Although after a year the graft became in phase with the surround again, the synchrony was not complete. In the first two experiments where follicle loss was considerable almost entire follicle groups seemed to have disappeared. In later experiments trio groups could usually be recognised, and so there was no evidence of primary follicle loss. However, secondary/primary follicle ratio fell by about 0.5 to 1, suggesting that the secondary follicles are more vulnerable. Although there was no significant difference in mean wool fibre diameter on the graft compared with the surround, the modal diameter was invariably and significantly greater. This is explained by preferential loss of small secondaries, rather than by a change in absolute diameter. The experiments showed that it is possible to provoke activity in seasonally quiescent follicles, but not possible to restrain activity by transplantation to a season of quiescence. The results support control by a combination of systemic and local factors, with the follicle, apparently able to override systemic effects.