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.

Changes in the frequency of the poll gene and the effect of polledness on production were measured from 1970 to 1979 in four closed lines of crossbred cattle. The lines were Africander cross (AX), Braham cross (BX) and two Hereford × Shorthorn (HS lines, one selected for production (HSS) and one a control line (HSR).Calves were classified as horned, polled or scurred. Except in the HSS line, horned males were more common than horned females. Horned HS bulls sired only horned calves when mated to horned cows but corresponding matings of AX and BX breeds produced some polled progeny. The incidence of scurs was highest in the AX line, lowest in the HS lines and higher in males than females. These observations are discussed in relation to existing models of inheritance of horn-type.Prior to 1970 the frequencies of the poll gene declined from their initial values in the BX and HS lines and increased in the AX line. These changes were ascribed to random genetic drift. After 1970 the frequency of the poll gene remained stable in all lines.No significant differences were observed between horned and polled cattle in live weight, fertility or mortality rates indicating that polledness had no detrimental effect on production in these lines.

Twenty-two unmated female Ayrshire twin cattle, that had initially been maintained for prolonged periods on one of six constant feeding levels until an equilibrium weight was attained, were subsequently moved up to higher constant feeding levels including ad libitum. In all, results were obtained for 44 equilibrium periods mostly of 96 weeks duration.For controlled feeding levels, the log^-log,. regression of equilibrium body weight on food intake, within animals, was 0-999 (s.e. 0045). For all results, including mature equilibria, the within-animal regression was 1-014. There was thus no systematic change in an individual's equilibrium maintenance requirement per kg body weight in the range from 25",, to 100",, mature. Efficiency of food utilization for equilibrium maintenance was found to be independent of age also, except for a small increase at advanced ages beyond 8 to 9 years.There were significant differences between animals in equilibrium maintenance efficiency, the genetic coefficient of variation being 6-4%. The most striking result, however, was a within-animal repeatability of 0-7, which meant that almost the same efficiency was re-attained when, after a prolonged period of many years on one constant feeding level, the same animal was allowed to re-establish a new equilibrium on a higher level.Following prolonged periods of food restriction, the animals showed remarkable capacity to recover in body weight even at very advanced ages, but nevertheless substantial stunting of mature weight did occur.

The effect of keeping the coats of weaner calves clipped throughout the year has been measured at Rockhampton. Clipping lowered body temperatures and significantly increased growth rate during summer but reduced growth rate, slightly and not significantly, during winter. Individual animals differing in natural coat type differed more in growth rate than would be expected from the effect of the difference in coat cover alone. Differences in growth rate were more consistently related to inherent coat type than to coat cover. It is concluded that coat type is significant as insulation and as a factor affecting efficiency of evaporative cooling, but also as a character correlated with other physiological attributes, some of which are thermoregulatory and some not thermoregulatory. A sleek coat is therefore associated with some qualities which may be advantageous in a cool climate, but the manifold significance of coat type is expressed in a warm climate.