Metabolism of Cystine by Merino Sheep Genetically Different in Wool Production IV. Rates of Entry of Cystine Into Plasma, Measured With a Single Intravenous Injection of L- [35S] Cystine, and the Subsequent Incorporation of 35S Into Wool Fibres

Abstract

Ten, 2-year-old Merino ewes from a flock selectively bred for high clean fleece weight (Fleece Plus) and ten from a flock bred for low clean fleece weight (Fleece Minus) were randomly divided between two dietary treatments: 600 or 1100 g/day of pelleted lucerne hay. After 14 weeks, each ewe received an intravenous injection of . Venous blood samples were collected at 15 specified times until 8 h after the injections, and wool fibres were plucked until 65-75 days after the injections.Protein-free filtrates prepared from blood plasma were bulked within sample times for ewes from the same flock and dietary treatment. Equations relating the specific radioactivity of free cystine isolated from the bulked filtrates to time after injection contained three exponential terms. The entry rate and pool size of cystine estimated from these equations were greater in Fleece Minus than in Fleece Plus ewes (by 25 and 44 % respectively for entry rate and pool size). Both traits were also higher in ewes offered 1100 g lucerne/day than in those offered 600 g/day (58·7 v. 33·9 mg/h for entry rate and 19·2 v. 11· 8 mg for pool size). The concentration offree cystine in plasma was greater in ewes offered 1100 g lucerne/day (3·0 v. 2·1 mg/I; P < O· 05), and greater in Fleece Minus ewes (3·0 v. 2·1 mg/I; P < 0·05).The percentage of the injected radioactivity recovered in the wool clipped to day 70 post-injection differed between genotypes and between dietary treatments (P < 0·05), being greater in Fleece Plus than in Fleece Minus ewes, and greater in those offered 1100 g lucerne/day than in those offered 600 g/day.The relationships between 35S incorporated per 1000 fibres (R) and time after injection (t) were best fitted by equations of the formFor all sheep, n = 3. The coefficient of the second term was significantly greater (P < 0·05) in ewes offered 1100 g lucerne/day, whilst the constant of this term was significantly greater in Fleece Minus ewes.The specific radioactivities of cystine incorporated into wool fibres (SR,) during various intervals of time after injection were derived from these equations and from the measured rates of output of cystine in wool. The equations computed to relate SR, to time after injection (t) were of the form 1=1Again there were three components. The coefficient of the third component was significantly greater

Whole body metabolism of cysteine and glutathione and their utilization in the skin of Romney sheep: consequences for wool growth

“…The measurements of cyst(e)ine ILR in the present study were 15-38 mmol/day (1-8-4-6 g/day); values which are somewhat higher than previously reported ILR values in sheep (Williams et at. (1972) 14 mmol/day; Williams (1976) 14-21 mmol/day; Pisulewski & Buttery (1985) 10 mmol/day; Fenn & Leng (1989) 12 mmol/day). Some of these differences may be related to the age and dietary intake of the animals studied.…”

“…The sheep in Expl 2 were lambs and showed higher cysteine ILRs (30-38 mmol/day) than the mature sheep used in Expt 3 (15 mmol/day) and other studies. The supplementation study of Fenn & Leng (1989) fed mature sheep a basal diet of only 800 g of oaten chaff a day and so it is perhaps not surprising that their basal ILR values were low as Williams et al (1972) and Williams (1976) demonstrated that cysteine ILR is significantly depressed with lowered intake. Williams (1976) also suggests that continuous infusion may underestimate ILR compared with a single injection approach because of the extent of [ 35 S]-recycling between free and disulphide-bound cysteine.…”

Cellular characteristics of wool follicles and fibres in finewool and strongwool Merinos

“…Similarly, systemic hormonal differences between genetically-different sheep are small and inconsistent (Williams et al 1986;Hynd 1988;Williams et al 1990), as are differences in the level of various metabolites, with the exception of cysteine (Williams et al 1972;Williams 1976). Difference in plasma cysteine levels between genotypes are probably a reflection of a differential ability of the follicles to extract and utilise the amino acid.…”

Studies on Veterinary Medicine

“…Cysteine is vital for wool growth and is usually the first limiting amino acid for wool fibre synthesis [171]. Sheep selected for high wool production tend to have lower blood cysteine and GSH concentrations than those selected for low wool production [128,290]. Low concentrations of GSH can be associated with impaired animal health as cysteine and GSH play a key role in the regulation of the immune response [79].…”