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This experiment was designed to measure the effects of infestation by B. microplus on cattle and to separate the effects of reduced food intake ("anorectic effect") from those due to the remaining factors of tick infestation ("specific effect"). Hereford cattle kept on a high-quality diet were studied over a treatment period of 11 weeks with the tick-infested animals being infested regularly with equal larval doses for each animal.

Plasma and red cell volumes were determined and the amounts of circulating metabolites deduced following heavy B. microplus infestation of Hereford steers fed a high quality diet. The experiment was designed to separate out effects of the cattle tick on host metabolism caused by reduced food intake ("anorectic effect"), and by other factors ("specific effect"). The specific effect caused a depression of the red cell volume and of the amounts of circulating haemoglobin, albumin, and total cholesterol and increases in the amount of circulating globulin. Anorectic effects were not significant.

In a flock of 229 three-year-old Border Leicester x Merino ewes it was found that ewes without lambs produced significantly more wool than ewes rearing single lambs, which in turn produced significantly more wool than ewes rearing twins. For all lamb-bearing ewes, the partial regression of fleece weight on slaughter weight of the lamb was -0.012 � 0.004 lb of fleece per 1 lb increase in slaughter weight. The fleece weight of the ewe was also related to the joining weight of the ewe and the breed of ram to which the ewe was mated. It is suggested that, unless it is carried out before their first mating, selection of ewes on a fleece weight basis will mitigate against the bearing of twins.

In one experiment studying the effects of delaying castration of bull calves from four or five months until eight months of age, under grazing conditions, there were significant differences in relative growth rate and body weights, while in another experiment, carried out at the same location in a later year, there were no differences, thus indicating a wide variability between years. In the second experiment an earlier castration (at approximately one month) was included, and some of the calves castrated at one month and at four months were implanted with testosterone propionate. There were significant differences in eye muscle area, but no differences in relative growth rates, body weights, and fat depth over eye muscle, between the group castrated at one month and those castrated at four or eight months, and between those with and without testosterone. It was concluded that testosterone secretion before puberty is of some biological importance.

At the age of approximately 11 months, 19 Angus steers were allotted to two experimental groups, namely, 10 to group A and 9 to group B. Group A animals were grown in pens and fed ad libitum. They were killed, two at each of the following of body weights: 250, 281, 316, 356, 400 kg. Group B animals were grown under similar conditions and killed at the same body weights as corresponding animals in group A; however, they were grown to weights 15% above their killing weights (growing-on phase) and then made to lose weight at 0.5 kg per day by restricting food intake until they reached their planned killing weights (weight loss phase). Huxley's (1932) allometric equation was used in logarithmic form as the basis for covariance analyses of the data. Empty body weight (EBW) increased as a proportion of full body weight as full body weight increased. EBW was higher in group A animals than in group B animals at the same full body weight, reflecting differences in weight of contents of the digestive tract. Dressed carcass weight increased as a proportion of EBW as EBW increased. Dressed carcass weight was higher in group B animals than in group A animals at the same EBW, indicating that the increase in carcass weight that occurred during the growing-on phase was not completely lost during the weight loss phase. During developmental growth, the weights of hide, feet, head, liver, gall bladder, heart, lungs, kidneys, and gut tissue decreased as proportions of EBW. The weight of abdominal fat increased as a proportion of EBW, while the weights of tail, spleen, and blood did not change significantly as proportions of EBW. During body weight loss, the weights of the feet, head, and tail remained close to the weights they had reached at the end of the growing-on phase, although, with the head, this varied considerably with the size of the animal before undergoing body weight loss. All other components lost weight during the weight loss phase. The hide, heart, lungs, and abdominal fat all reversed, approximately, the pattern of development that occurred during body weight growth. The liver, gall bladder, kidneys, gut tissue, spleen, blood, and thymus gland all lost more weight during the weight loss phase than they put on during the growing-on phase. With the liver, kidneys, and gut tissue, the proportion of weight lost varied according to the size of the animal before undergoing body weight loss.

Variations in the cross-sectional area of eye muscle of carcasses cut between the tenth and eleventh ribs were investigated, using 105 Hereford and 51 Angus steers aged 20 months. These cattle consisted of three groups, born in successive years. At constant carcass weight, statistically significant differences in eye muscle area were found between breeds and between years. Breed and year differences were also found in eye muscle area with width and depth of eye muscle constant, so that there are limitations to the estimation of eye muscle area from width and depth measurements. A nomograph is given for estimating eye muscle area from width and depth for Hereford and Angus cattle, when all animals are reared in the same year and environment. The use of eye muscle area as an indicator of weight of carcass muscle is discussed.

This paper describes part of an investigation of the effects of developmental growth and body weight loss on the carcass composition of Angus steers. A method of anatomical dissection was used on one half (the right side) of each carcass to find the weights of each carcass component. The results are compared with those obtained from a method of dissecting butcher's joints used on the other (left) half of each carcass. Two groups of steers were used in this experiment: group A, which grew continuously, and group B, which grew like group A and were then subjected to a period of weight loss before slaughter. Corresponding animals in both groups were killed at the same body weights. Statistical analysis was by analyses of covariance of weights of components converted to logarithms. As carcass weight increased, the proportions of muscle, bone, and fascia and tendons decreased, while the proportions of the fat components increased. This result was similar to that obtained. previously by joint dissection, but the changes differed in degree. Distribution of muscle and bone changed significantly as the total weights of these components increased. Distribution of the other components was known only in so far as they came from either the hindquarter or the forequarter; no changes were found in their distribution as their total weights increased. Comparison of group A and group B animals at the same carcass weight showed that body weight loss led to a significant increase in the proportion of bone in the carcass but only a slight decrease in the proportion of muscle. Body weight loss had a differential effect on the proportion of kidney and channel fat in the carcass, the result depending on the weight at which animals were killed. The weight of subcutaneous and intermuscular fat in the group B carcasses did not vary significantly from that of group A carcasses of the same weight. These results were similar to those found by joint dissection but there were differences in magnitude. In particular, the differences in muscle weight between group A and group B carcasses was more pronounced in the joint dissection, where it was statistically significant. Also bone weight from the joint dissection was affected differentially by the weight loss treatment at the different killing weights; however, there was no evidence of a differential effect on bone weight in the anatomical dissection. These differences were ascribed to more accurate separation of tissues in the joint dissection. Distributions of muscle, bone, and fascia and tendon were affected by loss of body weight. Unlike joint dissection, anatomical dissection did not show significant effects on the distribution of subcutaneous fat and intermuscular fat due to the weight loss treatment; these differences between results are ascribed to differences between the units used for assessing these distributions.

A least squares method particularly suited to automatic computation, for calculating adjustments to remove extraneous variation in performance test data, is described. Multiplicative adjustments can be calculated for discontinuous variables, e.g. sex, or for continuous variables, e.g. age at weaning. By calculation of all desired adjustments simultaneously each adjustment factor is as free as possible from the effects of the other variables. Results are given of the application of the technique to weaning weights of stud Hereford and Aberdeen Angus cattle reared on one property. With the use of several different models of analysis, the effects of age of dam, sex, year of birth, age at weaning, sire, and birth weight were investigated and comparisons drawn between the two breeds used, and between this study and other published work. The effect of some of these variables on birth weight is discussed, and the relative effects of some of the variables on weaning weight and birth weight compared. The use of a combination of traits to form a selection index is also discussed.

Changes in the blood composition of Hereford steers kept on a high. quality diet and infested with B. microplus were studied. The experiment was designed so that the effects on blood composition due to reduced feed intake ("anorectic effect") and those due to the remaining factors of tick infestation ("specific effect") could be independently estimated.