Resistance to the cattle tick, Boophilus microplus in a herd of Australian Illawarra Shorthorn cattle: Its assessment and heritability

Abstract

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.

A genome-wide association study of tick burden and milk composition in cattle

“…The genetic correlation between tick and milk traits was negative with large standard errors, while the heritabilities of these traits were similar to previous estimates. Compared with previous estimates the heritability for tick burden in this study was larger than the value of h 2 = 0.15 found in zebu and zebu composite Brahman and Tropical Composite cattle for tick scores (Prayaga et al 2009), but similar to the value of h 2 = 0.41 AE 0.08 calculated for taurine cattle using multiple tick counts (Henshall 2004) and within the range of h 2 = 0.34-0.49 previously calculated for cattle in Queensland (Wharton et al 1970;Mackinnon et al 1991). Heritabilities for the milk yields were similar to previously estimated values for these traits (Pander et al 1992) but higher than previous estimates restricted to Australian Holstein and Jersey (Visscher and Goddard 1995).…”

“…Tick numbers due to field infestations were counted in the size range 4.5-8.0 mm (Wharton et al 1970) on one side of the animal by more than one counter over more than one season. A count was considered usable if the average number of counts for that day was 20 ticks per side (Table 1).…”

Infestação experimental de equinos por Rhipicephalus (Boophilus) microplus

“…Para avaliação da resistência dos equinos, foi considerada a não recuperação de fêmeas ingurgitadas ou semi-ingurgitadas de R. microplus (animal resistente), a recuperação de poucas fêmeas semi-ingurgitadas (animal moderadamente resistente) e a recuperação de fêmeas ingurgitadas em número suficiente para realização do estudo (animal susceptível), conforme proposto por WHARTON et al (1970). As teleóginas de R. microplus recuperadas dos equinos foram levadas ao laboratório, lavadas em água corrente limpa e secadas com uso de papel toalha e pesadas em balança analítica de precisão.…”

Boophilus microplus : Cellular Responses to Larval Attachment and Their Relationship to Host Resistance

“…Resistance is immunologically mediated (Roberts 1968a) and the potential of the host to acquire a particular degree of resistance is heritable (Wharton et al 1970). In European breed cattle, resistance affects the establishment of each instar of this one-host tick, and it is particularly manifest against larvae in the first 24 h of their parasitic life (Roberts 1968b).…”