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.

The mean total skin thicknesses (mm) for the breeds sampled were: Devon 8.15, Hereford 6.7, Zebu cross 6.43, Australian Illawarra Shorthorn 6.23, Friesian 6.0, Zebu 5.77, Aberdeen Angus 5.75, Shorthorn 5.69, and Jersey 5.46. The early maturing Shorthorn (Bos taurus L.) and the Zebu (Bos indicus L.) differed significantly in the depth of the papillary and reticular layers, and in the relative thickness of these skin layers. The mean thickness for the papillary layer; was 0.98 mm in the Zebu, 1.40 mm in the Zebu cross, and 1.70 mm in the Shorthorn. Thus the larger, more active sweat glands of the Zebu are more superficial. The corresponding reticular layer averaged 4.45 mm in the Zebu, 4.5 mm in the Zebu cross, and 4.08 mm in the Shorthorn. The thickness of the papillary layer relative to the total skin thickness was 18.3, 23.7, and 29.3 per cent., for the Zebu, Zebu cross, and Shorthorn respectively. The Zebu and the Jersey have relatively thin skins. Therefore a thick skin is not essential for adaptability to a hot environment. Inherent differences in the function of the follicles and the glands of the papillary layer may be critical characteristics for heat tolerance.

Evidence is presented that the apocrine sweat glands of cattle have a temperature-regulating function. Under the stereo microscope, sweat droplets could be observed forming at the openings of the sweat gland ducts in response to intradermal injections of adrenaline, and during exposure to hot conditions. The sweat spots could be stained macroscopically, and prints showing the location of the spots were obtained with bromothymol blue papers pressed onto the skin surface. Quantitative measurements indicate that the evaporation of this sweat is the main source of heat loss in hot environments.

1. The object of this investigation has been to advance knowledge of the methods necessary for the practical application of the transplantation of fertilized ova in cattle.2. The induction of ovulation at any specific time can be produced by squeezing out the corpus luteum per rectum. Oestrus occurs from 2 to 4 days afterwards; this is accompanied by ovulation and the ova so produced are readily fertilized. The onset of oestrus after the expression of the corpus luteum is hastened by previous treatment with P.M.S.3. The induction of multiple ovulations is necessary to produce an augmented supply of fertilized ova, but it is of primary importance that the ova so produced are fertilized, viable and capable of full development. Four methods of doing this have been tested.

Skin samples taken with a trephine of known size from Shorthorn (Bos taurus L.) and Zebu (B. indicus L.) cattle were used to determine the density of hair follicles and apocrine glands in the skin. The repeatability of the measurement of density on the same animal was found to lie between 78 and 90 per cent. The expansion of the skin as the animal grows, and the manner in which the plane of nutrition can modify growth and so the extent of expansion, has a predominating effect on the hair follicle and apocrine gland density. There is a significant difference between ages, but for each breed the regression coefficients of log follicle number on log heart girth within age groups are not significantly different. The mean number of hair follicles per sq. cm in Zebus was 1698, in Zebu crosses 1321, and in Shorthorns on a low plane of nutrition 1064. In Shorthorns on a high plane the number was 764. All differences were statistically significant.