Multiple Country and Breed Genomic Prediction of Tick Resistance in Beef Cattle.

Ticks cause substantial production losses for beef and dairy cattle. Cattle resistance to ticks is one of the most important factors affecting tick control, but largely neglected due to the challenge of phenotyping. In this study, we evaluate the pooling of tick resistance phenotyped reference populations from multi-country beef cattle breeds to assess the possibility of improving host resistance through multi-trait genomic selection. Data consisted of tick counts or scores assessing the number of female ticks at least 4.5 mm length and derived from seven populations, with breed, country, number of records and genotyped/phenotyped animals being respectively: Angus (AN), Brazil, 2,263, 921/1,156, Hereford (HH), Brazil, 6,615, 1,910/2,802, Brangus (BN), Brazil, 2,441, 851/851, Braford (BO), Brazil, 9,523, 3,062/4,095, Tropical Composite (TC), Australia, 229, 229/229, Brahman (BR), Australia, 675, 675/675, and Nguni (NG), South Africa, 490, 490/490. All populations were genotyped using medium density Illumina SNP BeadChips and imputed to a common high-density panel of 332,468 markers. The mean linkage disequilibrium (LD) between adjacent SNPs varied from 0.24 to 0.37 across populations and so was sufficient to allow genomic breeding values (GEBV) prediction. Correlations of LD phase between breeds were higher between composites and their founder breeds (0.81 to 0.95) and lower between NG and the other breeds (0.27 and 0.35). There was wide range of estimated heritability (0.05 and 0.42) and genetic correlation (-0.01 and 0.87) for tick resistance across the studied populations, with the largest genetic correlation observed between BN and BO. Predictive ability was improved under the old-young validation for three of the seven populations using a multi-trait approach compared to a single trait within-population prediction, while whole and partial data GEBV correlations increased in all cases, with relative improvements ranging from 3% for BO to 64% for TC. Moreover, the multi-trait analysis was useful to correct typical over-dispersion of the GEBV. Results from this study indicate that a joint genomic evaluation of AN, HH, BN, BO and BR can be readily implemented to improve tick resistance of these populations using selection on GEBV. For NG and TC additional phenotyping will be required to obtain accurate GEBV.

Genomic Study of Babesia bovis Infection Level and Its Association With Tick Count in Hereford and Braford Cattle.

Bovine babesiosis is a tick-borne disease caused by intraerythrocytic protozoa and leads to substantial economic losses for the livestock industry throughout the world. Babesia bovis is considered the most pathogenic species, which causes bovine babesiosis in Brazil. Genomic data could be used to evaluate the viability of improving resistance against B. bovis infection level (IB) through genomic selection, and, for that, knowledge of genetic parameters is needed. Furthermore, genome-wide association studies (GWAS) could be conducted to provide a better understanding of the genetic basis of the host response to B. bovis infection. No previous work in quantitative genetics of B. bovis infection was found. Thus, the objective of this study was to estimate the genetic correlation between IB and tick count (TC), evaluate predictive ability and applicability of genomic selection, and perform GWAS in Hereford and Braford cattle. The single-step genomic best linear unbiased prediction method was used, which allows the estimation of both breeding values and marker effects. Standard phenotyping was conducted for both traits. IB quantifications from the blood of 1,858 animals were carried using quantitative PCR assays. For TC, one to three subsequent tick counts were performed by manually counting adult female ticks on one side of each animal's body that was naturally exposed to ticks. Animals were genotyped using the Illumina BovineSNP50 panel. The posterior mean of IB heritability, estimated by the Bayesian animal model in a bivariate analysis, was low (0.10), and the estimations of genetic correlation between IB and TC were also low (0.15). The cross-validation genomic prediction accuracy for IB ranged from 0.18 to 0.35 and from 0.29 to 0.32 using k-means and random clustering, respectively, suggesting that genomic predictions could be used as a tool to improve genetics for IB, especially if a larger training population is developed. The top 10 single nucleotide polymorphisms from the GWAS explained 5.04% of total genetic variance for IB, which were located on chromosomes 1, 2, 5, 6, 12, 17, 18, 16, 24, and 26. Some candidate genes participate in immunity system pathways indicating that those genes are involved in resistance to B. bovis in cattle. Although the genetic correlation between IB and TC was weak, some candidate genes for IB were also reported in tick infestation studies, and they were also involved in biological resistance processes. This study contributes to improving genetic knowledge regarding infection by B. bovis in cattle.

Sex pheromone of the American warble fly, Dermatobia hominis: the role of cuticular hydrocarbons.

Chemical communication between adults of the American warble fly, Dermatobia hominis (Diptera: Oestridae), was investigated by electroantennography and behavioral bioassays. Significant electroantennographic responses were recorded from both sexes to hexane-soluble cuticular lipids from either sex. Olfactometer tests indicated an attraction between males and females, and between females. Copulatory behavior of males with a white knotted string treated with female extract confirmed production of a sexual stimulant by females. Such behavior was not observed in tests with male extract, demonstrating that the pheromone acts also as a sex recognition factor. Cuticular hydrocarbons of sexually mature female and male D. hominis were identified by Gas chromatography-mass spectrometry and consist of a mixture of saturated n-, monomethyl-, and dimethylalkanes in both sexes. Sexual dimorphism was characterized by a higher relative concentration of dimethylalkanes in males and the presence of alkenes only in females.

Desempenho reprodutivo de Nasonia vitripennis Walker (Hymenoptera: Pteromalidae) em pupas crioconservadas de Chrysomya megacephala Fabricius (Diptera: Calliphoridae): avaliaçäo preliminar / Reproductive performance of Nasonia vitripennis Walker (Hymenoptera: Pteromalidae) on Chrysomya megacephala Fabricius (Diptera: Calliphoridae) cryopreserved pupae: preliminary evaluation

Avaliou-se o desempenho reprodutivo de Nasonia vitripennis Walker (Hymenoptera: Pteromalidae) em pupas de Chrysomya megacephala Fabricius (Diptera: Calliphoridae) previamente armazenadas a - 20ºC de temperatura, durante 77 dias, com e sem passagem prévia em nitrogênio líquido (NL) por um, três e 15 minutos. O grupo controle foi caracterizado por pupas hospedeiras frescas. Os muscóides foram expostos aos parasitóides durante 72 horas. Utilizou-se a relação de uma pupa muscóide por fêmea parasitóide. A amostra de pupas frescas permitiu a emergência de 15 parasitóides/ pupa, em média, enquanto 10 parasitóides / pupa emergiram dos espécimens prévia e diretamente armazenados em freezer (-20ºC). Observou-se um acentuado decréscimo do desempenho reprodutivo dos microhimenópteros que exploraram os substratos previamente submetidos ao NL durante um, três e 15 minutos (: 6,1; 5,5 e 5,7, respectivamente). A dissecação das pupas hospedeiras revelou um expressivo número de pteromalídeos imaturos, nas amostras que foram expostas ao NL, e de adultos faratos, em todos os tratamentos.