Genetic variation of seasonal tick counts in South African Nguni cattle

Tick and tick-borne disease are a major challenge in livestock production in the sub-tropics, with the advent of climate changes. The objective of this study was to assess tick species distribution and their colonisation on animals’ body sites, and to estimate genetic parameters for these tick traits in Nguni cattle. Data comprised seasonal tick counts on various anatomical regions of 586 Nguni cattle under natural infestation, in four herds located in four provinces of South Africa. Heritabilities and correlations for log-transformed counts were estimated using bivariate analysis, fitting a sire model, accounting for fixed effects. Six different tick species (Amblyomma hebraeum, Boofilids, Rhipicephalus evertsi evertsi, Rhipicephalus appendiculatus, Hyalomma marginatum, Rhipicephalus simus) were identified attached to eight anatomical regions (i.e. head, ear, neck,
back, legs, belly, perineum and tail) on the animals. Heritability estimates ranged from 0.01±0.01 to 0.26±0.01 across seasons and traits (anatomical region or tick species). Genetic correlations ranged from -0.79±0.33 to
1.00±0.00 among counts for different anatomical regions and 0.00±0.01 to 0.99±0.01 among tick species. Phenotypic correlations were low to moderate, ranging from 0.06±0.01 to 0.72±0.01 among anatomical regions and 0.01±0.02 to 0.44±0.01 for tick species. The largest genetic variation in tick count was observed in the summer (September to January). High genetic correlations were observed between whole body count and most of the anatomical region counts, with belly and perineum counts being the most suitable indicator traits for whole body count. Our results would allow identifying the most appropriate season and anatomical region for tick sampling in a cost-effective selection programme for tick resistance in Nguni cattle.