Search

Is well known the taurine and zebuine susceptibility to Rhipicephalus microplus. Few are the reports regarding tick population dynamics between the same herd/breed, and because of this, two experiments were performed. In the 1st, the cattle tick population dynamics in dairy nursing calves (reared collective and individually), weaning calves (4–16 months), heifers (17–29 months), cows in lactation and dry cows (≥ 30 months) from the same herd, tick burden and milk production correlation were performed, for two years. R. microplus females (4.5-8.0 mm) counts and the milk production were performed every 28 and 14 days, respectively. In the 2nd experiment, bovines belonging to different categories/age (newborn without previous contact with tick; 12–13 months with tick contact since birth; and 23–24 months with tick contact since birth) were experimentally infested with 30,000 R. microplus larvae, to quantify the number of fully engorged females detached from these animals. In the 1st experiment, when the mean counts of tick were ≥ 30 all animals of the group were treated. Nursing calves showed 3–4 peaks of ticks, animals reared individually showed smaller (p ≤ 0.05) tick burden than those reared collectively. Weaning calves (4–8 months) showed 5 tick peaks/year and higher mean tick burden was found than other categories. On the other hand, animals with 17–29 months of age showed smallest (p ≤ 0.05) tick burden, with 3 tick peaks/year. When the animal become lactating the tick burden increase, and 5 peaks/year occurred, and decrease again in dry cows (p ≤ 0.05) showing 4–5 tick peaks/year. Weaning calves and lactating cows received more acaricide treatments (p ≤ 0.05), 18 and 15, respectively. Nursing calves reared individually, and heifers (21–29 months) were the categories that received two acaricide treatments. The more milk the cow produce, more ticks it has (p ≤ 0.05). In the 2nd experiment, more (p ≤ 0.05) fully engorged females were recovered from younger animals than older ones. So, different tick control strategies need to be adopted in different dairy cattle categories, and the tick burden should be considered, once the effect may be more inherent to the animal rather than the strategy adopted. [ABSTRACT FROM AUTHOR]

Background and Aim: In tropical and subtropical countries, ixodid ticks are among livestock's most economically important ectoparasites. Although Nguni cattle from South Africa have adapted to harsh environments, it is unknown whether they will be resistant to ticks, and the diseases carried by ticks under various climatic conditions. Therefore, this study aimed to compare tick load and estimate the prevalence of different tick species among Nguni cattle under different environmental conditions. Materials and Methods: Tick counts were conducted monthly under natural challenges over 2 years on 586 Nguni cattle located at ARC-Roodeplaat and Loskop farms (warmer climate), Mukhuthali Nguni Community and the University of Fort Hare farms (cooler climate). The generalized linear model procedure of the Statistical Analysis System was used to analyze the data. It fitted the location (farm), sex, year, month or season, and animal age as covariates. Results: The tick species (relative prevalence) observed were as follows: Amblyomma hebraeum (42%), Rhipicephalus evertsi (22%), Rhipicephalus (Boophilus) spp. (16%), Rhipicephalus appendiculatus (11%), Hyalomma marginatum (5%), and Rhipicephalus simus (4%). Tick infestation was significantly affected by location, season, year, month of the tick counting and age of the animal. Loskop farm had the highest tick count (μ = 30.69) and showed the largest variation in tick count. Compared to the other seasons, higher tick counts were seen during the hot-dry (September–November) and hot-wet (December–February) seasons. A. hebraeum was the dominant tick species across all four farms, followed by R. evertsi. The perianal region (under the tail head), the perineum and the belly body locations were the most preferred tick attachment sites. Conclusion: These results provide useful information for developing appropriate control strategies for ticks and tick-borne diseases in these provinces of South Africa. Further work must investigate the feasibility of genetic improvement for tick resistance.

We tested whether holistic planned grazing (HPG) and four-camp grazing (FCG) rotational grazing approaches influence beef cattle parasites counts compared with continuous, season-long (SLG) grazing. We expected that parasite counts would increase linearly with increasing camp occupancy by cattle from 1 d (70-camp, HPG) to 21–28 d (four-camp, FCG) to 180 d (one-camp per season, SLG). Tick and faecal egg counts were observed across seasons on 30 steers raised on a private farm in Cedarville, South Africa. Tick species identified were Rhipicephalus evertsi evertsi, Rhipicephalus (Boophilus) decoloratus, Hyalomma spp. and Amblyomma hebreaum with respective prevalences of 32%, 29%, 20% and 19%. Unidentified roundworms had the highest faecal worm egg counts (81.2%) followed by Coccidia (16.4%), Nematodirus (1.2%) and strongyles (1.2%). Overall, prevalence and mean counts for ticks and faecal worm eggs were highest in the hot wet season, with the SLG having greater (P≤ 0.05) values than either of the rotational approaches. However, increasing camp number and animal densities above four camps did not reduce (P > 0.05) parasite loads compared with HPG. Current results suggest that rotational grazing is a potential strategy to reduce livestock losses caused by high tick and worm loads in cattle, especially in the hot wet season. [ABSTRACT FROM AUTHOR]

About 80% of the world's cattle are affected by ticks and tick-borne diseases, both of which cause significant production losses. Cattle host resistance to ticks is the most important factor affecting the economics of tick control, but it is largely neglected in tick-control programs due to technical difficulties and costs associated with identifying individual-animal variation in resistance. The present paper reviews the scientific literature to identify factors affecting resistance of cattle to ticks and the biological mechanisms of host tick resistance, to develop alternative phenotype(s) for tick resistance. If new cost-effective phenotype(s) can be developed and validated, then tick resistance of cattle could be genetically improved using genomic selection, and incorporated into breeding objectives to simultaneously improve cattle productive attributes and tick resistance. The phenotype(s) could also be used to improve tick control by using cattle management. On the basis of the present review, it is recommended that three possible phenotypes (haemolytic analysis; measures of skin hypersensitivity reactions; simplified artificial tick infestations) be further developed to determine their practical feasibility for consistently, cost-effectively and reliably measuring cattle tick resistance in thousands of individual animals in commercial and smallholder farmer herds in tropical and subtropical areas globally. During evaluation of these potential new phenotypes, additional measurements should be included to determine the possibility of developing a volatile-based resistance phenotype, to simultaneously improve cattle resistance to both ticks and biting flies. Because the current measurements of volatile chemistry do not satisfy the requirements of a simple, cost-effective phenotype for use in commercial cattle herds, consideration should also be given to inclusion of potentially simpler measures to enable indirect genetic selection for volatile-based resistance to ticks. About 80% of the world's cattle are affected by ticks and tick-borne diseases, with estimated economic losses from ticks ranging from US$20 to US$30 billion per year. Cattle host resistance is the most important factor affecting the economics of tick control, but it is largely absent in tick-control programs due to the difficulties and expense of identifying host tick resistance. The present paper reviews the literature to identify factors affecting resistance of cattle to ticks, so as to develop cost-effective ways of measuring tick resistance in cattle. The review recommends that three possible methods (haemolytic analysis; skin hypersensitivity reactions; simplified artificial tick infestations) be further developed to consistently, cost-effectively and reliably measuring cattle tick resistance. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

An experiment was conducted to study the variation in tick count amid different genetic groups of crossbred cattle viz, Sunandini and crossbred Fresian cattle in humid tropics and its association with body condition score and skin characteristics. The tick count and hair length were significantly (p≤ 0.05) high in crossbred Frisian compared to Sunandini cattle. While the body condition score had significant (p≤0.05) effect on tick count, coat score had no such marked effect. The skin thickness had significant (p≤0.05) positive correlation with tick count. [ABSTRACT FROM AUTHOR]

Ticks and tick-borne diseases are among the main causes of economic loss in the South African cattle industry through high morbidity and mortality rates. Concerns of the general public regarding chemical residues may tarnish their perceptions of food safety and environmental health when the husbandry of cattle includes frequent use of acaricides to manage ticks. The primary objective of this study was to identify single nucleotide polymorphism (SNP) markers associated with host resistance to ticks in South African Nguni cattle. Tick count data were collected monthly from 586 Nguni cattle reared in four herds under natural grazing conditions over a period of two years. The counts were recorded for six species of ticks attached in eight anatomical locations on the animals and were summed by species and anatomical location. This gave rise to 63 measured phenotypes or traits, with results for 12 of these traits being reported here. Tick count ( x ) data were transformed using log 10 ( x + 1) and the resulting values were examined for normality. DNA was extracted from hair and blood samples and was genotyped using the Illumina BovineSNP50 assay. After quality control (call rate >90%, minor allele frequency >0.02), 40,436 SNPs were retained for analysis. Genetic parameters were estimated and association analysis for tick resistance was carried out using two approaches: a genome-wide association (GWA) analysis using the GenABEL package and a regional heritability mapping (RHM) analysis. The Bonferroni genome-wide ( P < 0.05) corrected significance threshold was 1.24 × 10 −6 , with 2.47 × 10 −5 as the suggestive significance threshold ( P < 0.10) (i.e., one false positive per genome scan) in the GWA analysis. Likelihood ratio test (LRT) thresholds for genome-wide and suggestive significance were 13.5 and 9.15 for the RHM analysis. Six ixodid tick species were identified, with Amblyomma hebraeum (the vector for Heartwater disease) being the dominant species. Heritability estimates ( h 2 ) from the fitted animal and sire models ranged from 0.02 ± 0.00 to 0.17 ± 0.04 for the transformed tick count data. Several genomic regions harbouring quantitative trait loci (QTL) were identified for different tick count traits by both the GWA and RHM approaches. Three genome-wide significant regions on chromosomes 7, 10 and 19 were identified for total tick count on the head, total body A. hebraeum tick count and total A. hebraeum on the perineum region, respectively. Additional regions significant at the suggestive level were identified on chromosomes 1, 3, 6, 7, 8, 10, 11, 12, 14, 15, 17, 19 and 26 for several of the traits. The GWA approach identified more genomic regions than did the RHM approach. The chromosomal regions identified here as harbouring QTL underlying variation in tick burden form the basis for further analyses to identify specific candidate genes and polymorphisms related to cattle tick resistance and provide the potential for marker-assisted selection in Nguni cattle. [ABSTRACT FROM AUTHOR]

The objectives of the study were to estimate genetic parameters for tick resistance and to evaluate the effect of the level of tick infestation on the estimates of genetic parameters for South African Bonsmara cattle. Field data of repeated tick count records (n = 11 280) on 1 176 animals were collected between 1993 and 2005 by 10 breeders participating in the National Beef Recording and Improvement Scheme. The distribution of tick count records were normalized using a Box-Cox transformation. Data were divided into seven sub-data sets based on the mean tick count per contemporary group, to facilitate the investigation of the effect of level of tick infestation on the derived genetic parameters. A repeatability animal model including the fixed effects of contemporary group and age of animal at tick counting and random effects of the direct additive genetic, permanent environmental and residual effects was used to estimate genetic parameters using REML procedures. The additive genetic variance for tick count ranged from 0.01 to 0.08. The animal permanent environmental variance ranged from 0.00 to 0.03. Phenotypic variance decreased with increasing mean tick count level while additive genetic variance increased with mean tick count level. The heritability also increased with mean tick count level until a mean tick count level of ≥30. The highest heritability estimate obtained in the current study was 0.17 for data with mean tick count level ≥25. These results suggest that sufficient genetic variation for tick count exists in the Bonsmara cattle. Genetic selection for tick resistance is feasible even though genetic progress may be slow. [ABSTRACT FROM AUTHOR]