Intake and long-term cysteine supplementation change wool characteristics of Romney sheep

Sulfur amino acid supplementation increases wool production in sheep at low planes of nutrition but it is unclear whether there is any benefit of supp lementation at planes of nutrition above maintenance and what implications this might have for wool quality characteristics. This experiment directly investigated the interaction between sulfur supplementation and plane of nu trition in terms of wool growth and fibre characteristics. Twenty-four Romn ey ewes, acclimatised in individual metabolism units over a 7-week pre-trea tment period, were allocated to 1 of 4 treatment groups based on a 2 2 fact orial arrangement. Groups were low (L) or high (H) intake (0.8 or 1.3 maint enance, respectively) with continuous intravenous infusion of either saline (-Cys) or cysteine (+Cys, 2 g/day). During the 3-month treatment period, m easurements were obtained for liveweight, plasma cysteine concentration, wo ol sulfur concentration and output, clean wool growth, mean fibre diameter (MFD), length growth rate (LGR), colour, loose wool bulk, handle, and crimp frequency and character. Clean wool growth response (P < 0.05) to cysteine supplementation was greater for the L sheep (6.06 v. 4.31 g/100 cm(2)) tha n the H sheep (7.20 v. 6.13 g/100 cm(2)). The response to supplementation i n LGR (P < 0.01) was similar in both H (14%) and L (20%) sheep. There was n o response in MFD due to sulfur supplementation, although fibre diameter me asurements made along the fibres suggest that there was a response in L but not H sheep (P < 0.1). Wool sulfur concentration and output increased as a result of cysteine supp lementation but concentration increased more in L (30.6 v. 24.5 mg S/g; P < 0.01) than in H sheep (28.4 v. 26.2 mg S/g). Qualitative electrophoresis a nalyses suggested that the increase in wool sulfur was achieved primarily b y an increase in ultra-high-sulfur proteins. Crimp frequency and character were both significantly (P < 0.01) enhanced by cysteine supplementation. It is concluded that cysteine supplementation, at feed intakes that commonl y occur in the commercial situation, can produce a useful increase in wool growth. This growth increase is primarily accomplished by increasing length growth rate rather than fibre diameter, which should also improve the valu e of the wool fibre produced.