Maturing female ticks were counted in herds of Brahman x British, Africander x British, and British breed (Shorthorn x Hereford) cattle run together. About 3000 counts were made on over 1000 cattle. The Zebu crossbreds on average carried two-fifths the number of ticks carried by the British cattle, though in some herds the difference was greater, and it tended to be greater in females than in males, in summer than in winter, and in F2 than in F3 animals. Brahman cross and Africander cross cattle did not differ significantly in resistance. Male cattle carried significantly more ticks than females, and the resistance of lactating British breed cows, but not Zebu crossbreds, was lower than that of dry cows. Repeatability of counts was higher in females than in males, and higher in Zebu crossbreds than in British cattle. Expression of inherent resistance in the British cattle was variable according to circumstances which are only partly defined. Heritability estimates were up to 48%, but in some cases much lower. In the Zebu crossbreds there was little heritable variation in F, cattle, but in subsequent generations heritability was estimated as 82%. The needs for selection for resistance, and the control of error and the prospects of success, are discussed.

Selection and breeding for tick resistance in an Australian Illawarra Shorthorn (AIS) herd was undertaken from 1966 to 1971. Mating of half the AIS herd with a Brahman bull in 1968–69 provided a comparison of tick resistance in selected Bos taurus and crossbred B. taurus x B. indicus cattle. Parent cows and their progeny were ranked for resistance to ticks, infestations of which were acquired as a result of grazing infested pastures, and from periodical artificial infestation with cohorts of c. 20,000 larvae of Boophilus microplus. Ranking and assessment of resistance levels were based on counts of semi-engorged female ticks on the right side. Parent cows selected for high resistance consistently carried fewer ticks than cows selected for low resistance. Mating of cattle selected for high resistance produced progeny that were significantly more resistant than the progeny of cattle selected for low resistance. However, the Brahman bull, which had slightly lower resistance than the AIS bull, produced progeny with higher resistance, even when mated with AIS COWS selected for low resistance. Pregnant cows were significantly less resistant than non-pregnant cows, and lactating cows were very much less resistant than non-lactating cows. Young cows were more resistant than older cows. Calves at foot carried fewer ticks than their dams when grazing infested pastures, but after weaning they were less resistant than their parents when resistance was determined from artificial infestations. Female calves carried fewer ticks than males on almost all occasions, but differences were not significant in winter. Significant seasonal changes in resistance were demonstrated in AIS and Brahman x AIS weaner and yearling cattle. All cattle were less resistant in winter. Changes were greatest in Brahman x AN females, on which the average numbers of female ticks that matured following artificial infestations in January 1970 (summer), July 1970 (winter) and January 1971 (summer) were 151, 1046 and 95 respectively.

The effect of natural infestations of internal parasites (Cooperia species, Haemonchuspbcei, Oesophagostomum radiatum, and Trichostrongylus axei) and the cattle tick Boophilus microplus on the growth rate from weaning to 21 months of age of 93 F3 Africander x Hereford and Shorthorn (AX), Brahman x Hereford and Shorthorn (BX), and Hereford x Shorthorn (British) was studied. All animals were weighed, ticks counted, faeces sampled, and the animals treated at fortnightly intervals. Faecal egg counts were used as an index of internal parasite burdens, and tick infestations assessed according to the number of females between 0.45 and 0.8 cm in length on one complete side of the animal. Breed differences for the internal parasitic burdens were small and were only significant (P<. 0.05) for O. radiatum. The BX cattle carried the highest burdens. The BX cattle were significantly more resistant to tick infestations than the AX group, which in turn were significantly more resistant than the British group. Males carried significantly more ticks than females. Parasites had little or no effect on gains while the animals were gaining weight rapidly, and it was only after a cessation of gains due to deteriorating pasture conditions that significant treatment effects became evident. Treatment had the largest effect on the British and very little effect on the BX group. Regressions of gains on parasitic burdens within treatments were all negative. The repeatabilities of a series of egg counts for the species were significant, Haemonchus egg counts having the highest repeatabilities. Correlations between egg counts of Cooperia spp and 0. radiatum, and H. placei and T. axei were significant (r = 0.82, P < 0.001; and r = 0.23, P < 0.05). Internal parasites significantly depressed packed red cell volume, haemoglobin concentration, and plasma protein levels. There were significant negative correlations of egg counts of O. radiatum with haemoglobin concentration and packed cell volume of the Zebu crossbreds (r = 0.46 and v = 0.47, P < 0.01).

Observations of cattle in central and southern Queensland are collated to define the prevalence and area of Stephanofilaria lesions associated with infestations of the buffalo fly, Haematobia irritans exigua. The observations were made on herds that were being used for other purposes. In a survey of ~1500 animals at Belmont in central Queensland in 1982, 98% of cows and 70% of calves had lesions. Most lesions were on the neck and dewlap and 10% were raw and weeping at the time of sampling. The total area of lesions per animal was strongly related to cattle breed and age. Old Bos taurus animals had the greatest area of lesions, whereas young Bos indicus had the least. Heritability estimates were low, averaging 0.01 for calves and 0.18 for cows. A smaller survey of cows and steers at Craighoyle in central Queensland in 1986 showed a higher numbers of lesions and positive correlations between the total lesion area and animal size. The lesion area increased with tick survival, suggesting that tick-resistant animals are also resistant to Stephanofilaria infection. Steers had smaller areas of lesions than cows, as found previously with cattle ticks. Long-term monitoring observations in central and southern Queensland between 1981 and 1986 showed that the total area of lesions was seasonal with a peak in late summer, consistent with the seasonal incidence of buffalo fly. Animals segregated into Low and High lesion herds maintained their differences over time. The lesions penetrated the dermis of the cattle hides and rendered the affected area unusable, but few lesions occurred on valuable parts of the hide so such economic effects are likely to be insignificant. One animal nearly died of a haemorrhage from a lesion on the dewlap and had to be treated. The results can inform policy on buffalo fly control, and biosecurity preparations in relation to the potential establishment of the Old World screw-worm fly, Chrysomyia bezziana, in Australia, which will be facilitated by the lesions. The results emphasise the significant animal welfare and biosecurity risks posed by the lesions in northern Australia.

The effects of heavy infestations of tick (B. microplus) on the blood composition of Shorthorn X Hereford steers on low and high planes of nutrition were studied.