The potential for harvesting weakened wool: a comparison of several sheep breeds in terms of staple strength and depilation force after cyclophosphamide treatment

Abstract

Five sheep from each of seven groups (breeds or strains) were dosed with 15 mg cyclophosphamide (CPA) per kg body weight. An equal number of controls were left undosed. The groups were Dorset Horns, Border Leicester x Merino crossbreds (BLM), Corriedales, Polwarths, South Australian strongwool Merinos (SWM), medium Peppin Merinos (MWM) and fine-wool Merinos (FWM). The force and energy to break staples clipped from the back wool of the 70 sheep were measured before and 103 days after dosing with CPA. The strength of the belly wool prior to dosing only was measured. Depilation forces and the length of plucked staples in wool from the back and the belly were measured in all sheep at dosing (day 0) and 7, 14, 23 and 89 days after dosing. Wool growth after CPA dosing was monitored by dyebanding. The lengths of plucked staples increased with time for the control sheep, but remained constant for the dosed sheep because the fibres in the latter broke at their weakened zone instead of being pulled from the follicle. The Polwarths and Corriedales had the longest staples and the FWM the shortest.

There were breed differences in the energy but not the force required to break staples in untreated sheep. This was probably related to the breed differences in staple length and crimp structure; the longer-stapled breeds generally required more energy to break the staple than did those with shorter staples. Belly wool required about 20–40 N/kTex or 0.4–0.7 J/kTex to break a staple, compared with values of 50–60 N/kTex or 0.8–1.9 J/kTex for back wool. Staple-breaking force for treated sheep (range 1–32 N/kTex) was much less than for the controls (36–67 N/kTex), but with depilation force there was some overlap (1–18 N/kTex treated; 8-23 N/kTex control), which indicated that different factors are measured when depilation forces of treated and untreated sheep are determined. The relationship between depilation force and staplebreaking force was good, although curvilinear (R = 0.98), in treated sheep, but poor in untreated sheep (r = 0.13). Energy to break staples was less well correlated with depilation force.

There were breed differences in response to CPA. The FWM, BLM and Dorset Horns showed the least response in terms of staple-breaking force (treated values 22%, 25% and 26% of control values respectively) or depilation force, while the MWM (16%), Corriedale (13%), Polwarth (10%) and SWM (7%) showed progressively greater responses. These differences were considered to be related to differences in body condition rather than to different sensitivities of the follicles to CPA. There appeared to be no effect on the length growth rate of the wool from the treated sheep as measured by the rate of movement of a dyeband applied at day 0. Only three sheep which had lost insignificant (< 1%) amounts of wool after 104 days could be defleeced by hand. Another five were readily defleeceable by hand but had lost 5–60% of their wool. Another eight sheep could have been defleeced with difficulty by hand. The remainder all showed the effect of CPA in that the majority of fibres, when subjected to tension, broke instead of being pulled from the follicle. It was concluded that there may be a role for machine harvesting of weakened wool, but there was no future for hand harvesting.