Effects of Grafting the Skin in Merino Sheep, With Special Reference to the Growth of Wool and Hair

Abstract

Grafts of wool-growing trunk skin (wool grafts) and hair-growing inguinal skin (hair grafts) were studied in two black and two black and white adult Merino sheep. Skin growing black wool was transplanted to skin growing white wool and vice versa. Also, skin in both black and white regions was excised and returned to the same site. Inguinal skin was transplanted to black wool-growing skin.The areas of the grafts, which initially ranged from about 1 to 25 cm 2 , decreased to a minimum by 28 days after grafting. Most grafts then expanded slowly and returned to approximately their original size by the end of the experiment (118-194 days after grafting).Grafting caused the temporary cessation of wool and hair growth. Old fibres were shed and new fibres, usually similar in colour, appeared above the skin surface about 28 days after grafting. Each animal was given a series of injections of L-[35Sjcystine and fibres were sampled from the grafts and control regions for length and diameter measurements. The fibres on most of the grafts showed marked increases in length growth rate and diameter, resulting in large increases in volume growth rates. However, the total amount of wool produced by the grafts was usually reduced because grafting caused a loss of follicles.At the end of the experiment, skin samples were taken from the grafts and control regions for microscopic examination. The sebaceous glands were retained in the grafts except those associated with follicles that did not regenerate. The sweat glands and erector muscles were often destroyed by grafting, particularly in the wool grafts. Innervation was greatly reduced. Langerhans cells appeared to be as numerous in the grafts as in control samples. Melanocytes spread from black skin into wool and hair grafts of white skin and were most commonly seen in the epidermis, which increased in thickness. Clumps of pigment in the dermis appeared at the periphery of many of the grafts.

Pigmented Spots in the WoolBearing Skin of White Merino Sheep Induced by Ultraviolet Light

“…The development of pigmented wool follicles parallels the field observations (Fleet and Forest 1984); in both cases it appears that the epidermal melanocytes are able to migrate along the outer-root sheath to the follicle bulb, capping the dermal papilla, from where melanin granules transfer to adjacent keratinocytes in the developing wool fibre. The migratory ability of melanocytes has been proposed as a mechanism whereby pigmented wool-bearing skin develops in non-pigmented regions of Suffolk and black Merino sheep following trauma (Lyne and Hollis 1968) and after skin grafting in grey and white skin patches on black Merino and Soay sheep (Ryder and Priestley 1979;Lyne and Hollis 1980). The requirement of melanocytes to migrate from the epidermis via the outer-root sheath to the follicle bulb, rather than the activation of existing or precursor melanocytes within these regions, agrees with the observed distribution of melanocytes in white Merino sheep .…”

Wool follicles initiate, develop and produce wool fibres in ovine fetal skin grafts

“…The reduction in the number of follicles initiated in grafted skin and the loss of some pre-existing follicles during grafting in older fetal skin, were probably a result of the grafting procedure and the transient disruption of the vascular supply to the skin. Loss of follicles has also been observed in autografts of adult Merino wool-growing skin (Lyne & Hollis 1980). The rate of development of initiated and pre-existing follicles in skin grafts was in advance of that which occurred in control fetal skin.…”

“…The cause of this is unknown, but it may reflect an increase in nutrient availability to the follicles, as a result of the reduced follicle density. Lyne & Hollis (1980) suggested that this possible increase in nutrient supply may come about through increased blood flow following destruction of cutaneous nerves at grafting. However, the cutaneous innervation of fetal skin in the present study would have been relatively undeveloped (D. E. Hollis, personal communication) compared with that in the adult skin grafted by Lyne & Hollis (1980).…”

“…Lyne & Hollis (1980) suggested that this possible increase in nutrient supply may come about through increased blood flow following destruction of cutaneous nerves at grafting. However, the cutaneous innervation of fetal skin in the present study would have been relatively undeveloped (D. E. Hollis, personal communication) compared with that in the adult skin grafted by Lyne & Hollis (1980). Follicle development occurred predominantly within the peripheral zone of the grafts, whereas the central region of the graft contained a sparse distribution of both initiated follicles and/or follicles that existed in the skin prior to grafting.…”

Characterization of Melanocytes in Wool-bearing Skin of Merino Sheep

“…In the wool-bearing skin of white Merino sheep, a possible control mechanism in the local tissue environment is suggested by the fact that although melanocytes are absent from the wool follicle they are present in the epidermis and have the potential to change their level of expression (Fleet and Forrest 1984;Lyne and Hollis 1980). Further studies are needed in order to determine the influence of the specific components controlling the distribution and activity of melanocytes in white Merino sheep.…”