Ana Lúcia Campos

Genetic diversity of four cattle breeds using microsatellite markers

Four cattle breeds (Gyr, Nellore, Guzerat and Holstein) were analyzed by amplification of genomic DNA using microsatellite loci to evaluate the genetic diversity within and among them. DNA samples of 18 animals from each breed were collected to access the genetic content of them. Allele frequencies were calculated and used to generate a Neis genetic distance matrix what was used to build a dendrogram following UPGMA clustering. As expected, Holstein breed was the most distinct from the other breeds: 1.15 in relation to Gyr, 1.12 in relation to Nellore and 0.94 in relation to Guzerat. The closest genetic distance was 0.25 between Guzerat and Nellore. A total of 64 alleles in all four breeds were detected using nine microsatellite primers. Each breed showed 53% of the total number of alleles. The average number of alleles per locus was 7.11 ± 3.21. The most informative locus was BMS1237 with 53% of observed heterozygosity and the least informative locus was BMS3004 with 12% only. The average heterozygosity detected for the nine loci were 35% and the expected value for Hardy-Weinberg equilibrium was 53%. This low heterozygosity suggests a high endogamy level among the animals sampled within each breed.

Association of the bovine major histocompatibility complex (BoLA) BoLA-DRB3 gene with fat and protein production and somatic cell score in Brazilian Gyr dairy cattle (Bos indicus)

The effect of the bovine major histocompatibility complex (BoLA) locus on animal health may be due to a direct action of its alleles on immune functions, whereas its indirect effect on production traits might be explained by the better general health conditions of more productive animals. In the present study, the BoLA-DRB3 gene was investigated in 1058 cows belonging to seven Brazilian Gyr Dairy herds (Bos indicus, Zebu cattle). A total of 37 alleles were identified, 15 of them described for the first time in a Zebu breed. A highly significant association (p < 0.02) was observed between allele *54 and a decrease (-26.1 kg) in milk protein yield and there was a significant association (p < 0.05) between this allele and lower (-26.07 kg) milk fat yield. There was also a significant association (p < 0.05) between allele *6 and decreased (-12.47 kg) milk protein and allele *7 and increased (12.72 kg) milk protein. There were also indications of association (p < 0.10) between somatic cell score (SCS) and alleles *3 (SCS increased by 0.54 units) and *31 (SCS increased by 0.46 units). The highly significant association of allele *54 with lower protein yield suggests the possible use of this allele in marker-assisted selection programs.

Molecular characterization of elephantgrass accessions through RAPD markers

O cultivo do capim-elefante e limitado por variacoes na producao de biomassa e por reducoes na qualidade e disponibilidade de forragem, tornando prioritaria a busca de genotipos com menor sazonalidade de producao. Para verificar a extensao da variabilidade genetica entre cultivares contrastantes, 10 acessos foram analisados via amplificacao do DNA pela tecnica RAPD. Foram utilizados 44 primers aleatorios, que produziram um total de 160 bandas de DNA, sendo que 23% das bandas analisadas foram monomorficas para todos os acessos. Os dados binarios, originados dos geis (1-presenca, 0-ausencia), foram utilizados para gerar uma matriz de distâncias geneticas, que foi utilizada para uma analise de agrupamento segundo o metodo da media das distâncias (UPGMA). Os acessos mais divergentes dos demais foram Cameroon e Vruckwona, com distâncias geneticas medias de 0,34. Os acessos com menores distâncias geneticas medias dos demais foram Pioneiro e CNPGL 27-5, ambos com uma distância genetica media de 0,25. As distâncias geneticas, considerando todas as analises, variaram de 0,06 a 0,43, indicando uma variabilidade genetica pouco acentuada, embora os acessos estudados sejam bastante contrastantes em relacao a morfologia e fisiologia.

Associação do loco BoLA-DRB3.2 com produção de leite em bovinos da raça Gir

The association between BoLA-DRB3.2 alleles identified by PCR-RFLP and milk production in Gir breed was studied using molecular and phenotypic data of 424 Gir cows. Genetic data consisted of animal genotypes for BoLA-DRB3.2 alleles and 305-day-milk-yield. The association between BoLA-DRB3.2 alleles and a putative QTL affecting the trait was investigated by mixed model with an animal model. BoLA-DRB3.2 locus was found to be highly polymorphic in Gir breed, showing seven alleles (BoLA-DRB3.2*4, *8, *11, *19, *28, *41 e *48) that have not been yet described in Zebu animals. Two BoLA-DRB3 alleles (*16 e *29) were significantly associated with milk production, suggesting that BoLA-DRB3.2 locus itself or a linked QTL influences 305-day-milk yield of Gir cows.

Quantitative trait locus affecting birth weight on bovine chromosome 5 in a F2 Gyr x Holstein population

Segregation between a genetic marker and a locus influencing a quantitative trait in a well delineated population is the basis for success in mapping quantitative trait loci (QTL). To detect bovine chromosome 5 (BTA5) birth weight QTL we genotyped 294 F2 Gyr (Bos indicus) x Holstein (Bos taurus) crossbreed cattle for five microsatellite markers. A linkage map was constructed for the markers and an interval analysis for the presence of QTL was performed. The linkage map indicated differences in the order of two markers relative to the reference map (http://www.marc.usda.gov). Interval analysis detected a QTL controlling birth weight (p < 0.01) at 69 centimorgans (cM) from the most centromeric marker with an effect of 0.32 phenotypic standard-error. These results support other studies with crossbred Bos taurus x Bos indicus populations.

Quantitative trait loci (QTL) mapping for growth traits on bovine chromosome 14

Quantitative trait loci (QTL) mapping in livestock allows the identification of genes that determine the genetic variation affecting traits of economic interest. We analyzed the birth weight and weight at 60 days QTL segregating on bovine chromosome BTA14 in a F2 resource population using genotypes produced from seven microsatellite markers. Phenotypes were derived from 346 F2 progeny produced from crossing Bos indicus Gyr x Holstein Bos taurus F1 parents. Interval analysis to detect QTL for birth weight revealed the presence of a QTL (p < 0.05) at 1 centimorgan (cM) from the centromere with an additive effect of 1.210 ± 0.438 kg. Interval analysis for weight at 60 days revealed the presence of a QTL (p < 0.05) at 0 cM from the centromere with an additive effect of 2.122 ± 0.735 kg. The region to which the QTL were assigned is described in the literature as responsible for some growth traits, milk yield, milk composition, fat deposition and has also been related to reproductive traits such as daughter pregnancy rate and ovulation rate. The effects of the QTL described on other traits were not investigated.