A system of subjective scoring of cattle coats, ranging from very sleek to very woolly, is described. It has been applied to about 1600 animals, of which 500 were Hereford and Shorthorn cows and the rest their progeny from matings in four years to British breed and Zebu bulls. Consistency of scoring within and between observers is satisfactory. Highly significant differences between animals of the same breed persist through different seasons. The repeatability of coat score is 0.6 or more over intervals of up to 17 months. Effects of season, age, and sex are described. Heritability of coat score is estimated at 0.63. Coat scores are well correlated with body temperatures and respiration rates. Coat score and post-weaning growth rate of British breed calves are correlated to such a degree that coat score can be superior to a record of body weight as an estimate of growth capacity. The genetic correlation between coat score and growth rate is high in the British breeds. Evidence of the relation between coat score and growth rate in Zebu cross calves is inconclusive. The observed relationships are discussed with particular reference to their physiological causes. The results indicate the potential value of coat characters in selecting tropical beef cattle. The degree to which these results may be applicable to other populations in other environments is discussed. It is concluded that a sleek coat is important in favouring heat dissipation, but it may have even greater significance as an indicator of metabolic efficiency or of capacity to react favourably to stress.

Rectal temperatures of breeding cows at the National Cattle Breeding Station, ‘Belmont’, Rockhampton were recorded in each of 2 years. The data analysed represented two Bos taurus (Hereford × Shorthorn) and four B. indicus × B. taurus half-bred lines, and 800 to 900 cows in each year. Rectal temperatures averaged 39·8°C, and were 0·5°C higher in British breed than in zebu-cross cows and 0·3°C higher in lactating than in dry British cows (no effect in zebu cross).Fertility, measured as success or failure in producing a calf at term, was affected by rectal temperature (P<0·0001 in both years). The relationship was curvilinear, the reduction in calving rate due to 01°C increment in temperature being 0009 at 39°C, 002 at 40°C and 0035 at 41°C. Response of fertility to a given change in rectal temperature was the same in different breeds. The average depression of fertility due to heat susceptibility was 015 to 0·25 in British-breed and approximately 010 in zebu-cross herds.Even in relatively heat-tolerant zebu crossbreds and in a relatively mild environment on the Tropic, both the mean rectal temperature and its genetic variability within a herd had quite large effects on reproduction. The heritability of rectal temperature was 0·25 (s.e. 012) and its genetic correlation with fertility was −0·76 (s.e. 0·35). There was a parallel effect of rectal temperatures of cows on the birth weights of their calves.

An Australian Illawarra Shorthorn herd of 24 cows was mated in three consecutive years with an AIS bull. The cows and their progeny were rated for tick resistance at frequent intervals from August 1959 to December 1965 by counting the numbers of semiengorged female ticks on the right side. The mean of log counts for all counts on a particular animal was adopted as the reference value for its degree of susceptibility. The ranking of cattle generally showed a high level of consistency with mean repeatability of counts (r = 0.47, P < 0.01). Discrimination between animals was more reliable (P < 0.01) in summer (r = 0.52) than in winter (r = 0.27). The repeatability of tick counts increased with mean count, from r = 0.27 when the mean count was 3 to r = 0.67 when it was 100. The reliability of counts on the cows decreased with age and with lactation. Supplementary information on a larger herd showed no effect of pregnancy on mean count or on discrimination between susceptible and resistant animals, but showed that there was a partial breakdown of resistance during lactation. In calves infested naturally, no effects of age or sex on tick counts or their repeatability were detected, though male calves yielded significantly larger numbers of ticks than females when infested artificially. The mean yield of mature female ticks on the cows following two artificial infestations with known numbers of larvae ranged from 0.2 to 27.4% of the potential. Natural and artificial assessments of susceptibility were closely correlated. The rank of the bull was similar to that of the more resistant cows. Mean estimates of the heritability of tick resistance based on single counts were 39 % from dam-calf correlations and 49 % from full-sib correlations. Estimates based on summer counts only were 42 and 64% respectively. These results provide strong encouragement for selecting for tick resistance.

Rectal temperatures of cattle grazed near the tropic of Capricorn in central Queensland were studied. The cattle were of Bos indicus, B. taurus and crossbred lines, and were represented by over 200 growing heifers in each of 2 years and some supplementary groups.Rectal temperatures were loge normally distributed when they were expressed as deviations from a basal temperature of 38°C. They were significantly repeatable, but were more highly repeatable when herd mean temperature was above 39·5°C. The heritability estimate was 0·33 (P < 0·01).The mean phenotypic regression of growth rate on rectal temperature, within breed groups, was 0·04 (s.e. 0·006) kg/day per °C (r = 0·3, P < 0·01) over the entire growth period from birth to 18 months of age but greater during warmer seasons. The estimated genetic correlation was insignificant in one group of heifers but −0·86 (s.e. 0·17) in the other.The evidence of favourable and possible unfavourable responses to selection of cattle for low rectal temperature in warm environments is discussed.

Approximately equal numbers of Shorthorn x Hereford (British), Africander x British, and Brahman x British yearlings (all F3-F4 generations), totalling 117, were run together on one pasture. One-third of each breed type was dipped every 3 weeks to control ticks, one-third was given injectable tetramizole at the same intervals to control gastrointestinal helminths, and one-third was untreated. The estimated increases in gains in body weight in 27 weeks due to dipping were 10 kg (10%) in Africander cross and 3 kg (3%) in Brahman cross animals (neither significant), but 27 kg (46%) in Shorthorn–Herefords (P 0.001). Anthelmintic treatment increased gains by 22 kg (22%) in the Africander cross (P < 0.001), and 1 kg (1%) in the Brahman cross group (not significant), and 18 kg (30%) in the Shorthorn–Herefords (P < 0.01). The differential breed responses to the presence of ticks were accounted for by differences in the numbers of female ticks maturing. The Africander and Brahman cross animals carried a mean of 20–30 ticks per side ompared with75–100 on Shorthorn–Herefords, and had higher repeatability of counts on individual animals. The regression of weight gain on tick count between animals within infested groups was similar to that between infested and dipped groups. There was no breed difference in counts of helminth eggs in faeces. There were significant differences between animals but they were not correlated with weight gain. Tick burdens were moderately high. Helminth egg counts were low. In these circumstances and under the pasture conditions represented, tick resistance accounted for 40% of the superiority in growth of the Brahman cross or Africander cross over Shorthorn–Herefords, and tolerance of helminths accounted for none of the difference between Africander cross and Shorthorn–Herefords, for 25–40% of the difference between Brahman cross and Shorthorn–Herefords, and for more than the observed difference between Brahman and Africander crosses. The effects of both parasites on growth, and the importance of differential responses of breeds, are conditioned by environmental conditions, notably nutrition.