Hair follicle activity and fibre growth were studied using histological sections from the skin of five adult feral does sampled every four weeks for 18 months. The main period of guard hair growth in primary follicles was from November to April. Secondary follicles grew fine, long, nonmedullated fibres (cashmere) from December to June. Shedding of these fibres from secondary follicles had commenced by July and cashmere was absent from the fleece by November. From September to December a subsidiary hair cycle occurred in many secondary follicles which produced minute (vellus) fibres, less than 2.4 mm in length. Some secondary follicles probably shed their cashmere fibres and remain quiescent over spring. Annual pelage changes were therefore achieved with one main growth period, although many secondary follicles underwent another brief hair cycle in spring.

In vivo effects of local infusion of a variant of insulin-like growth factor-I (IGF-I), long-R3-IGF-I, into the skin were investigated using six conscious sheep with food available ad libitum. An artery and vein on the abdominal flank of each animal, as well as the saphenous artery, were catheterized so that infusion of isotopically labelled amino acids, with or without IGF-I, could be used to determine amino acid uptake by arteriovenous difference in combination with blood flow determined by dye dilution. Measurements were made on each animal prior to IGF-I infusion, at hourly intervals for the 4 h of IGF-I infusion into the skin artery, then 2 and 4 h after IGF-I infusion ceased. Numbers of cells replicating in the bulbs of wool follicles in the IGF-I-infused area and in the skin on the contralateral side of each animal were measured after labelling with 5-bromo-2'-deoxyuridine. IGF-I caused a significant increase in the skin blood flow (P < 0.05), utilization of oxygen (P < 0.05), uptake of cysteine (P < 0.05) and phenylalanine (P < 0.001), and the rate of utilization of cysteine (P < 0.05) for protein synthesis. IGF-I increased amino acid uptake regardless of whether the skin was in negative or positive amino acid balance prior to infusion. During the recovery period amino acid utilization by skin returned towards preinfusion levels. No effects of IGF-I were found on replicating cell numbers in the bulbs of wool follicles.

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Sheep fed on either a low (500 g lucerne (Medicago sativa) chaff/d; L) or high (1 100 g lucerne chaffld; H) intake had measurements made, using arterio-venous techniques, of blood flow and energy metabolite and cysteine utilization in the skin. Sheep on the H intake had significantly increased skin blood flow (P = 0.014) and oxygen uptake (P = 0.05). Although the H sheep had higher skin blood flow they showed no difference in skin uptake of either glucose or acetate compared with the L sheep, but the €5 sheep had a significantly lower output of lactate (P = 0.014). Animals in each group had either ['4C]glucose or ['4C]acetate infused into the skin which showed that acetate was the predominant precursor of skin sterol and fatty acid synthesis in the H sheep while L sheep skin used both glucose and acetate. The H sheep showed an increase in the net uptake of cysteine by the skin (P = 0.053), and in the uptake of cysteine for protein synthesis (P = 0.078), relative to the L sheep and this increase was of a comparable magnitude to the increase in blood flow to the skin. Although blood flow, protein synthesis and energy supply increased in the skin of the H sheep by 200-300 %, wool production would only have increased by 10-20%, suggesting that nutrient flux changes are not the sole level of regulation of wool production.Skin energy metabolism: Cysteine: Feed intake: Sheep Regulation of metabolism in the skin of sheep is of productive significance in two ways; first, and directly, because of the significant role of wool production within skin metabolism, second because of the potential for partitioning nutrient supply to the skin, away from other body tissues. Such partitioning could result either in the skin sparing metabolites for use by other tissues or, alternatively, retaining metabolites to the detriment of other tissue function.Studies of protein metabolism in the skin of sheep (Lobley et al. 1992) and preruminant lambs (Attaix et al. 1988) suggest that in early life skin has a similar protein fractional synthesis rate (FSR; g protein synthesis/d per g tissue protein) to that of muscle. However, by adult life skin has a higher FSR than that of muscle and makes almost an equal contribution to total body protein synthesis. The results of Lobley et al. (1992) also demonstrated that skin FSR was sensitive to the level of feed intake, but the study was not able to discriminate the processes by which skin regulates these responses to intake. For example, intake-sensitive changes in FSR could be via a modification of blood supply (and thus flux of nutrients to the skin) or through a change in the uptake rate of Iimiting amino acids by the skin cells. Blood flow to the skin is itself subject to rapid and large changes consequent on the requirements of thermoregulation. These influences can confound measurements of intake responses.The role of energy metabolites in regulation of skin metabolism is unclear. Harris et al. (1989) in a preliminary arterio-venous-difference study of skin metabolism found that * For reprints...

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