No abstract

Skin specimens from 495 Australian Merino ewes were collected from 22 flocks, including 9 parent studs out of the 17 identified in the contemporary population. Flocks from all of the 4 important strains of the Australian Merino are represented. The skin samples were collected by a standard biopsy method devised for the purpose by the authors, and histological sections prepared. The techniques are described and data for the following estimations presented: mean total (np+z) follicle population density; mean primary (np) follicle population density; ns/np ratio; mean primary (dp) fibre diameter; mean secondary ( da ) diameter; mean fibre diameter of the composite population (dp+s); mean ratio of primary and secondary fibre diameters (dp/ds). For each flock the mean and standard error of the estimations are tabulated and the range of individual values observed summarized for each of the four Merino strains. The data are presented as the material on which further more detailed analyses will be made; the need is stressed for extending these studies, which form an important basis for genetic studies of fleece structure in the Merino and other breeds. Attention is also drawn to certain extreme variants in the hair follicle group, one of which (a very small group) may prove to have a simple hereditary origin.

Skin biopsy specimens were collected at a standard midside position from 321 individual cattle (Bos taurus L.) of known age or in defined age groups on pastoral properties in New South Wales and Queensland. Beef cattle were represented by samples from the breeds: Aberdeen Angus, Devon, Hereford, and Shorthorn. Dairy cattle were represented by samples from the breeds: Australian Illawarra Shorthorn, Holstein-Friesian, Jersey, and Red Poll. Data were also obtained on 30 beef Shorthorns repeatedly sampled from birth to the age of 2-1/2 years under severe drought conditions in north Queensland. In all specimens each hair follicle was associated with an apocrine gland as well as a sebaceous gland and an arrector pili muscle. Thus, all hair follicles were homologous with the primary follicles of sheep; no secondary follicles were at any time observed; hence, there was no follicle group comparable in its complexity to that in the sheep and many other mammalian species. Further and more systematic observations by the biopsy and histological methods used in this work are necessary to examine the true nature of breed differences in the follicle and apocrine gland population density of the skin. The Jersey appears to have a denser coat. The data presented in this paper emphasize the dual importance of age and nutritional status of the animal on the hair follicle population density.

Female Sprague-Dawley (CD) rats were exposed to 2450-MHz (CW) microwave radiation at incident power densities of 0 or 28 mW/cm2 for 100 min daily on the 6th through 15th day of gestation. The whole-body specific absorption rate at 28 mW/cm2 is estimated to be 4.2 W/kg. These exposure conditions raised rats' average colonic temperatures to 40.3 degrees C at the end of irradiation. There were 67 sham-irradiated and 70 microwave-irradiated females. When these groups were compared, no significant differences were found in pregnancy rates; in the numbers of live, dead, or total fetuses; in the incidences of external, visceral, or skeletal anomalies or variations; or in the body weight of live fetuses. It is concluded that these conditions do not have an effect on the gross structure of the fetal rat when applied repetitively during post-implantation pregnancy. It is also strongly suspected that this lack of an effect may hold true at any exposure level less than that which will kill a significant number of the dams by hyperthermia (colonic temperature greater than 40 degrees C).

Two experiments have been conducted with young Lincoln, Corriedale, Polwarth, and fine Merino maiden ewes to compare the growth of fleece by these breeds and to assess relations between the growth of fleece and some factors, nutritional and non-nutritional, likely to influence its growth. In both experiments four representatives of each breed were kept in a sheep house in single pens and fed a high quality diet of constant composition. The second experiment followed immediately on the first and the same sheep were used except for necessary replacements. In the first experiment, which lasted for about one year, the intake of the diet was continuously unrestricted; in the second the intake of the diet was progressively restricted by ordered steps and was finally maintained for 12 weeks at one-fifth of the unrestricted intake of the first 4 weeks of the experiment. With few exceptions, the absolute or relative values of the characters measured formed a smooth series from the fine Merino through the Polwarth and Corriedale to the Lincoln-either in ascending order (e.g. food and water intake; liveweight and chest dimensions; fibre thickness, length, and volume; clean wool, suint, and total skin products output; clean wool and suint output per unit food intake) or descending order (e.g. total and primary follicle density; ratio of secondaries to primaries; wax output and wax output per unit food intake) or showed little or no difference between the breeds (e.g. body length and height; food intake per unit net liveweight; total skin products per unit food intake). The relative positions of the breeds as shown in the first experiment mere generally maintained in the second as food intake was progressively reduced. The results of the two experiments were combined for the individuals and a series of partial regression analyses were undertaken to determine the regression of some variables of fleece production on the level of food intake, atmospheric temperature, fleece weight, and experimental time. Self-selected food intake decreased with increase in fleece weight and less obviously with increase in experimental time (or, possibly, with deposition of subcutaneous fat). Water intake increased with both increase in food intake and rise in atmospheric temperature. Wool weight produced, and fibre thickness, length, and volume growth, all increased with increase in food intake, and within the limits of observed food intake the relation between wool growth and food intake was adequately represented by linear regression. Increase in atmospheric temperature exerted no significant influence on wool growth, except by the Lincolns (through fibre thickness). A positive regression of wool growth rate on fleece weight, acting through fibre length growth, was found, but change in fibre thickness was not related to increase in fleece weight. Wax production was positively related to increase in food intake and negatively to rise in atmospheric temperature. Suint production was positively related to both food intake and fleece weight. Wool, wax and suint production per unit food intake decreased with increase in food intake. Wax per unit food intake decreased with rise in temperature and suint per unit food intake increased with increase in fleece weight.

SummaryThyroidectomy of the newborn lamb prevents the maturation of secondary wool follicles. The administration of L-thyroxine to thyroidectomized lambs allows normal follicle development.Body growth and wool growth are also depressed by thyroidectomy and most thyroidectomized lambs do not survive more than a few weeks without replacement therapy. The effects on wool growth do not appear to be secondary to the effects on follicle development.The thyroxine requirements for normal wool growth and for normal secondary follicle maturation appear to be greater than the requirements for general body growth. I. INTRODUCTIONThe development of wool follicles in the lamb has been described by Carter (1943), Carter and Hardy (1947), Burns (1949), Fraser (1954, Schinckel (1953Schinckel ( , 1955, and Short (1955). Primary follicles are fully developed and are producing fibres at birth. Development of most if not all secondary follicles commences by the time of birth but in the Merino only about 20 per cent. of secondary follicles are producing fibres at this time. In the first month after birth this proportion increases to 70-80 per cent. Further development then occurs more slowly.The thyroid is well known to affect growth and differentiation. Simpson (1924) found that thyroidectomy of lambs retarded growth and reduced fleece weights at 13-14 months of age by 50 per cent. but no observations were reported on follicle development. The hair cycles of rats are greatly retarded by thyroidectomy (Salmon 1938; Scow and Marx 1945;Scow and Simpson 1945; Dicke 1948), and the administration of throxine to normal rats has been reported to accelerate the hair cycle (Butcher 1937). The lamb does not exhibit several cycles of wool development similar to the hair cycles in the rat, but development of individual follicles appears to be a similar process in both species. This paper reports the results of an experiment carried out to determine the effect of the thyroid on the maturation of the secondary follicles of the lamb. The results show that the thyroid does markedly influence this process.

Since wool-growth rate is strongly influenced by the plane of nutrition, any measure of inherent wool-producing capacity in the sheep must take this into account, and the relation of these three factors to each other must be known. On general grounds, the relation of wool-growth rate to nutrient intake seems likely to follow the familiar law of diminishing returns which introduces the concept that for each sheep there may be an asymptotic value of wool-growth rate characteristic of the individual. From this and other considerations, it was postulated that these relationships could be described by an equation of the form where y = wool-growth rate, x = nutrient intake rate at or above maintenance levels, Xo = the nutrient intake rate for which y = 0, A = the asymptotic value of y, and k' = a constant dependent on the nutritive qualities of the diet employed:

Skin specimens from 494 ewes were collected in flock samples of 11-23 animals, mostly 8-18 months old, from Australian and overseas sources among the following breeds: Corriedale, Polwarth, Lincoln, English Leicester, Border Leicester, Romney Marsh, Southdown, Dorset Horn, Suffolk, Ryeland, Scottish Blackface, Welsh Mountain, Swaledale, Cheviot, Wiltshire, and Swedish Landrace. The specimens were taken by a standard biopsy method and evaluated in the manner described by Carter and Clarke (1956). For each flock sample the mean, standard error, and range of individual values were recorded for the following estimates : total (np+s) follicle population density; primary (np) follicle population density; ns/np, ratio; primary fibre diameter (dp); secondary fibre diameter (2,) ; fibre diameter of the composite population (dp+s) ; of primary and secondary fibre diameters (dp/ds) . The data supplement those recorded for the Australian Merino sheep (Carter and Clarke 1957), and demonstrate the small hair follicle groups apparently characteristic of most British short-, long-, and carpet-wool breeds in well-marked contrast to the large groups in the skin follicle population of the Australian Merino. This difference between the Merino and other breeds may be general except where new breeds have developed from crossing with the Merino or its derivatives, when hair follicle groups of intermediate size may be found as in the Corriedale and Polwarth.