In vitro analysis of nutrient uptake by skin from fine wool and strong wool Merinos.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 19 IN VITRO ANALYSIS OF NUTRIENT UPTAKE BY SKIN FROM FINEWOOL AND STRONGWOOL MERINOS J. E. HOCKING EDWARDS and P. I. HYND Dept of Animal Sciences, Waite Agricultural Research Institute, Glen Osmond, S.A. 5064. Genetic differences in wool growth do not appear to arise from differences in voluntary feed intake nor in nutrient digestion and absorption from the digestive tract (Williams 1987). This implies that wool growth differences may be associated with nutrient supply and uptake from the blood and extracellular fluids, efficiency of utilisation of nutrients within the follicle, or a combination of these factors. We have recently demonstrated differences in blood flow to the skin (Hocking Edwards and Hynd 1991) and in the volume of germinative bulb tissue in the skin (Hocking Edwards and Hynd 1992), between high and low wool producing sheep. This paper examines the in vitro rate of uptake of glucose and cysteine by wool follicles from 2 strains of Merino sheep. Four strongwool (high-wool producers) and 4 finewool (low-wool producers) Merinos with mean (k s.e.m.) liveweights of 53 (& 0.7) kg and 48 (+ 0.6) kg, respectively, were housed indoors and each fed 1 kg of grain-based pellets per day for 190 days. Wool growth was measured on the midside using the tattoo patch technique. Skin strips (2 mm by 25 cm) taken under local anaesthesia (lignocaine hydrochloride, 20 mg/mL) were immediately placed in Krebs-Ringer buffer (pH 7.2) and then incubated with 35S-cysteine and 3H-glucose for 3 h (37�C; 5% Co2/95% 02). The tissue was then washed in 5% (w/v) trichloroacetic acid, solubilised in Soluene 350 (0.8 mL) and stored overnight in HCl(1 mol/L; 1 mL) and scintillant (ACS II, 5 mL), after which nutrient uptake was estimated by liquid scintillation counting (LKB Wallace Beta counter). Table 1. Wool growth per unit area of skin and in vitro nutrient uptake by skin from strongwool and fmewool Merinos (s.e.m. in parentheses) CPM, counts per minute Different letters indicate significant differences at P = 0.05 One-way analyses of variance indicated that there was a significant difference in the rate of uptake of glucose (P<O.O5), but no significant difference in the rate of uptake of cysteine between the strongwool and finewool Merinos (Table 1). It can be concluded that, in vitro, skin of strongwool Merinos has a greater rate of uptake of glucose than finewool Merinos. This may result from a high energy requirement needed to maintain the greater volume of germinative tissue associated with high wool production (Hocking Edwards and Hynd 1992). Nevertheless, variation in wool production between strains of Merinos was not due to a differential ability of the skin to absorb cysteine from an extracellular pool. Whether these characteristics are retained in vivo, with the added effects of blood flow and other physiological factors, is still being examined. HOCKING EDWARDS, J. E. and HYND, P. I. (199 1). Proc. Nuts. Sot. Aust. 16: 206. HOCKING EDWARDS, J. E. and HYND, P. I. (1992). Aust. J. Agric. Res. 43: 355-65. WILLIAMS, A. J. (1987). In ` Merino Improvement Programs in Australia.' (Ed. B. J. McGuirk.) p. 482. (Australian Wool Corporation.) 150