Abstract
The objective of the study was to characterise genetic parameters across months for different tick species and anatomical locations in South African Nguni cattle. Tick counts were conducted monthly, over a 2-year period, on 586 Nguni cattle under natural infestation, from four herds located in different provinces of South Africa. The counts were recorded for six species of ticks (Amblyomma hebraeum, Rhipicephalus evertsi evertsi, Rhipicephalus decoleratus and microplus (Boofilids), Rhipicephalus appendiculatus, Rhipicephalus simus and Hyalomma marginatum) attached on eight anatomical locations on the animals and were summed by species and anatomical location. Heritability estimates, phenotypic and genetic correlations were estimated on a monthly basis using mixed linear models, fitting univariate and bivariate sire models. Fixed effects considered were location, sex, year and age as a covariate. Tick counts were higher in the hot months, and A. hebraeum was the most dominant tick species. Heritability estimates for tick count varied by month and trait and ranged from 0 to 0.89. Genetic correlations were mostly positive, and low to high, with some negative correlations with high standard error. Phenotypic correlations were low to moderate. In general, high genetic correlations were observed between whole body count and the anatomical location counts, suggesting that it may not be necessary to conduct whole body counts. Counts from the belly and perineum appeared to be the most suitable surrogate traits for whole body count. These findings provide useful information for developing strategies for the practical implementation of genetic selection, as a supplement to the traditional tick control measures.
Highlights
Economic losses in livestock production due to ticks and tickborne diseases have long been a major concern to livestock producers in tropical and sub-tropical regions including South Africa (Seifert 1984; Passafaro et al 2015; Mota et al 2016)
Tick count data were collected from 586 randomly selected Nguni cattle (61 males and 525 females) over a 2-year period from four different herds in different agro-climatic zones: Agricultural Research Council (ARC) Loskop Research Farm located in the Limpopo Province of South Africa (n = 124), ARC-Roodeplaat Research Farm located in Gauteng Province (n = 143), Mukhuthali Nguni Community Farm located in the Kwa-Zulu Natal Province (n = 224) and the University of Fort Hare Farm in Alice located in the Eastern Cape Province (n = 95)
The mean monthly whole body tick counts were lowest (8.4 ± 6.1) in June (Winter) and highest (32.1 ± 23.4) in November (Summer); similar trends were observed for the other traits analysed (Table 2), except for Boofilids which had highest mean values in March
Summary
Economic losses in livestock production due to ticks and tickborne diseases have long been a major concern to livestock producers in tropical and sub-tropical regions including South Africa (Seifert 1984; Passafaro et al 2015; Mota et al 2016). The most economically important tick genera affecting livestock production in Southern Africa are Rhipicephalus (includes the genus formerly known as Boophilus), Amblyomma and Hyalomma (Marufu et al 2011; Nyangiwe et al 2013; Mapholi et al 2013, 2016). These tick genera have an impact on animal productivity directly through heavy infestation and indirectly through transmission of tick-borne diseases One possibility is the identification and use of cattle that are naturally resistant to ticks (Hayward 1981)
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