Effects of Freezing the Skin and Plucking the Fibres in Sheep, With Special Reference to Pigmentation

Abstract

SummaryMacroscopic and microscopic changes in the skin of seven adult Suffolk and Merino sheep were studied for periods of up to 513 days following the application of solid carbon dioxide to hair-and wool-growing areas after clipping or plucking of the fibres. Observations were also made on the effect of plucking alone.A colour change from black to whit,e occurred in the coat subsequent to freezing skin which previously grew black hair in Suffolks and black hair or black wool in Merinos. In contrast, follicles which grew white wool in Suffolks and in an isolated white area on an otherwise "black" Merino sheep were induced to grow black or partially coloured fibres for periods ranging from a few days to several months when damaged by freezing the skin or plucking the fibres. The outer root sheaths of the follicles in the regions which normally grew white wool in these animals were the only source of the melanocytes which appeared near the dermal papillae of regenerating follicles and passed pigment into the new fibres. When the skin was frozen after the fibres had been plucked, the melanocytes in the follicle outer root sheaths were usually destroyed and the new fibres were non-pigmented.Other changes which frequently resulted from freezing the skin were an increase in the thickness of the epidermis, destruction of the sweat glands, a reduction in the number of follicles per unit area of skin, and a reduction in the innervation of the skin. No follicle neogenesis was seen. An increase in the length of the fibres, due either to an increased growth rate or to an increase in the duration of the growth cycle, sometimes occurred.

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

“…However, they reported that the epidermis was of normal thickness 1 year after grafting. The increases in epidermal thickness reported here were similar to those obtained following freezing the skin of sheep (Lyne and Hollis 1968b).…”

“…Ryder and Priestley (1979) described the loss of pigment and repigmentation of the epidermis and fibres after freezing grafts of Soay sheep skin for 30 min. Similar loss of pigment and repigmentation of the epidermis, but not the fibres, was described by Lyne and Hollis (1968b) following freezing the pinnae of Suffolk sheep for 4 min. Repigmentation of the few grafts that lost pigment was not observed in the present experiments.…”

“…The sebaceous glands were retained but the sweat glands and erector muscles were often lost from the grafts as they were following freezing (Lyne and Hollis 1968b). Priestley (1965) and Ryder and Priestley (1977) also reported that sweat glands and erector muscles were often lost from grafts of wool-and hair-growing skin in sheep.…”

“…The distribution of alkaline phosphatase (AP) and acetylcholinesterase (AChE) was investigated in frozen sections 50 /lm thick. Paraffin sections, cut vertical to the skin surface and stained with haematoxylin, eosin, and picric acid (HEP), were used for the measurements of mean epidermal thickness by the method of Lyne and Hollis (1968b).…”

Morphological and Protein Synthesis Changes in Skin during Wool Follicle Regeneration after Plucking and Mimosine Administration

“…actively growing fibres), and a morphological study of the regeneration of such follicles after plucking was made. The results obtained supplemented the descriptions of earlier workers (Johnson 1965;Silver et al 1967;Lyne and Hollis 1968;Lyne et al 1974) and enabled an accurate comparison of the regenerative events with those described by Reis et al (1975) for the regeneration of wool follicles after mimosine treatment. The protein synthesis activity of wool follicles during regeneration after plucking and after mimosine treatment was also lexamined by measuring the distribution of radioactivity in extractable skin proteins after they were labelled in vitro with [3H]leucine.…”