A small proportion of Zebu genetic background in crossbred calves may not be enough to improve resistance against natural bovine Babesia spp. infections

The main objective of cattle breeders in tropical and subtropical regions is to acquire animals with taurine-productive traits adapted to the broad weather range of these regions. However, one of the main challenges on using taurine genetics in these areas is the high susceptibility of these animals to tick-borne diseases. Consequently, the present study evaluated from 10 November 2021-19 April 2022, the over 13 assessments, the Babesia bovis and Babesia bigemina DNA loads and the IgG anti-B. bovis and anti-B. bigemina levels in Angus (n = 17, 100% Taurine) and Ultrablack (n = 14, ∼82% taurine and 18% Zebu) calves. Data were analyzed using a multivariate mixed model with repeated measures of the same animal including the fixed effects of evaluation, genetic group, sex, Babesia spp., and their interactions. The repeatability values were estimated from the (co)variances matrix and expressed for each species. The correlations between the DNA loads (CNlog) and IgG titers (S/P) values for the two species were also estimated using the same model. Regarding the specific IgG antibody titers for both Babesia spp., no significant differences were observed between the two genetic groups. However, for B. bovis and B. bigemina DNA loads, Ultrablack calves presented significantly higher values than Angus calves. Under the conditions evaluated in this study, our findings suggest that the low percentage of Zebu genetic in the Ultrablack breed was insufficient to improve resistance against babesiosis. Further studies must demonstrate if the low percentages of Zebu genetics in Taurine breeds can modify the susceptibility to babesiosis infections.

Resistance to natural tick infestation varies with age and coat and hair traits in a tropically adapted beef cattle breed

Rhipicephalus (Boophilus) microplus causes considerable livestock production losses. Knowledge of the traits that influence tick resistance contributes to the development of breeding strategies designed to improve herd productivity. Within this context, this study evaluated the resistance of Caracu, a tropically adapted cattle breed, to R. microplus. Tick count, hair length, coat thickness, and coat color were evaluated in 202 naturally tick-infested females (cows and heifers) over a period of 18 months. Blood samples were collected from all animals during the winter season for hematological analysis. Data were analyzed using Pearson correlations, generalized linear models, and principal component analysis. Correlation coefficients of tick count with coat color, coat thickness, and hair length were estimated within each season. Hematological parameters were only included in the winter season analysis and were analyzed by the restricted maximum likelihood method using log-transformed data. No differences in blood parameters were observed between animals with and without ticks. However, tick count was negatively correlated with erythrocytes (-0.29) and hematocrit (-0.24) and positively correlated with mean corpuscular hemoglobin (0.21) and mean corpuscular hemoglobin concentration (0.25). These findings suggest that higher tick counts lead to a decrease in erythrocytes but also to an increase in the amount of hemoglobin per erythrocyte, which could reduce the damage caused by low erythrocyte levels due to tick hematophagy, delaying or preventing anemia. Although tick infestation on pasture was demonstrated by the infestation of all staff members during herd management, none of the animals exhibited high tick counts, providing evidence of resistance of Caracu animals to R. microplus. Tick infestation was influenced by age class (cows > heifers), season (spring and summer > fall and winter), coat thickness (>1.5 mm > <1.5 mm), and hair length (>6 mm > <6 mm). Three components were extracted by principal component analysis, which accounted for 69.46% of data variance. The findings of this study will contribute to the development of efficient strategies aimed at reducing economic losses due to tick infestation and could be applied in animal breeding to select for tick resistance traits, reducing chemical control strategies and consequently improving sustainable livestock production.

Estimation of genetic parameters for the tick and hemoparasite burden in Angus cattle

The study was conducted with the objective of estimating genetic and phenotypic parameters for tick (CRM) and Babesia bigemina (IBBi), Babesia bovis (IBBo), and Anaplasma marginale (IAM) burden in Angus female breed in Brazil. The sample group was composed of Angus females raised in herds located in a region of endemic instability for cattle tick fever in the state of Rio Grande Sul (RS), Brazil. The variance components were estimated using Bayesian inference and Gibbs sampling algorithm, considering a multi-trait animal model. Heritability estimates showed values of low magnitude, ranging from 0.03 (IBBo) to 0.16 (CRM), while repeatability estimates ranged between 0.07 (IBBo) and 0.21 (CRM). Regarding the genetic correlation estimates, the values showed low (-0.01 for IBBo × IAM) to moderate (0.55 between IBBi × IAM) magnitudes. The results indicate that it is possible to use tick count and hemoparasite infection levels as selection criteria, with small genetic gains.

Identification of novel allelic patterns and evolutionary lineage of BoLA MHC class II DQA locus in indicine and taurine cattle

Among different cattle types, Bos indicus are known for their ability to better resist the tropical microbial infections comparatively, wherein MHC molecules play a significant role. In this study allelic diversity at MHC locus, DQA of Bos indicus, Bos taurus and crossbred of taurine-indicus has been explored to understand the possible role of MHC region in differential immune response. Thirty nine different DQA alleles were identified, out of which 14 were novel, along with documentation of duplication of DQA alleles. Indicus cattle population presented diverse types of DQA alleles compared to crossbred and exotic. Translated amino acid sequence analysis indicated, codon 64 and 50 of peptide binding sites being highly polymorphic and most of the indicus cattle presented alanine and arginine amino acid at position 64 and 50. Within breed genetic variation found to be higher than between breeds. Because of their ability to bind and subsequently respond to a wide array of antigens, the newly identified DQA alleles with high diversity present in the form of duplicated haplotypes in different combinations in cattle populations provided significant insights into probable role of this MHC locus in better tropical disease combating ability and genetic fitness of indicus cattle.

Semi-quantitative evaluation of Babesia bovis and B. bigemina infection levels estimated by HRM analysis

Bovine babesiosis is economically the most important arthropod-borne disease of cattle worldwide. The most significant damage caused by bovine babesiosis is attributed to Babesia bovis due to its higher pathogenicity. This study aimed to develop a real-time PCR method followed by HRM (high-resolution melting) analysis for the simultaneous detection of B. bovis and B. bigemina, enabling a semi-quantitative analysis of Babesia levels using a single-tube reaction. The HRM was compared with real-time PCR using species-specific hydrolysis probes. The HRM analysis allowed to differentiate both Babesia species and was sensitive in the detection and differentiation of 10% for each Babesia species in the sample. Our results suggest the use of this method to estimate the prevalence of infections by B. bovis or B. bigemina as an alternative to the methods of absolute quantification by real-time PCR since it neither requires precise estimates of the number of DNA loads nor the construction of calibration curves. The simultaneous detection of the two Babesia species can be used to characterise the infection levels in cattle populations from different geographical regions, allowing a better control of these diseases.

Humoral and Cell-Mediated Immune Response Validation in Calves after a Live Attenuated Vaccine of Babesia bigemina

The current vaccines to control bovine Babesia bigemina (B. bigemina) infection are not fully protective and vaccination failures incur heavy losses to the cattle industry around the world. Using modified micro-aerophilous stationary phase, we developed a culture-derived attenuated live vaccine against B. bigemina and tested a single subcutaneous inoculation of 2 × 10⁸ infected erythrocytes in calves. The protection was measured after a lethal intravenous challenge with 5 × 10⁸ virulent calf-derived B. bigemina. Our results demonstrated that a single shot of attenuated vaccine was capable of inducing robust humoral and cell-mediated immune responses in calves. We found a significant increase in the IgG antibody titers post-challenge and a strong proliferation of both CD4+ and CD8+ T cells contributing towards the protection. Our vaccine provided complete protection and parasitic clearance, which was followed for more than 100 days post-challenge. This immunity against babesiosis was directly linked to strong humoral responses; however, the parasitic clearance was attributed to significant T cells effector responses in vaccinated calves as compared to the infected control calves. We anticipate that these results will be helpful in the development of more efficient culture-derived vaccines against Babesia infections, thus reducing significant global economic losses to farmers and the cattle industry.