Polimorfismo do gene GoLA-DRB.2 e detecção de Mycoplasma agalactiae e Mycoplasma mycoides cluster em rebanhos caprinos nos estados de Pernambuco e Paraíba, Brasil

Abstract

The program of selection of goats with milk aptitude has been focused on the increase in milk quantity, neglecting factors related to resistance to diseases and milk composition. This behavior has led to studies aimed at the rapid detection of microorganisms and the identification of genes or chromosomal regions related to infectious diseases of the mammary gland. The objective of the present thesis was to detect Mycoplasma agalactiae (Ma) and Mycoplasma mycoides cluster (Mmcluster) in goat milk samples and to evaluate the composition and counting of somatic cells from Ma and Mmcluster positive animals (Experiment 1). In addition, we sought to identify Goat Lymphocyte Antigen (GoLA-DRB.2) gene polymorphisms and to associate them with goat milk characteristics (Experiment 2). To perform the experiment 1, 373 samples of goat milk of different races belonging to herds located in the states of Pernambuco and Paraiba were collected. The genomic DNA of the milk samples was extracted by the silica / guanidine isothiocyanate method, followed by the generic and species-specific amplification by polymerase chain reaction. Identification of the presence or absence of gene products was performed by direct observation of the bands of the PCR products visualized on electrophoresis gel. Analysis of variance and comparison tests of averages were performed to verify the effects of positivity on somatic cell composition and counting characteristics. The frequencies for Ma and Mmcluster were 43.21% and 5.70%, respectively, in the herds evaluated. The breeding system was considered as risk factors (p <0.001) and the racial pattern (p<0.001). Ma positive samples were detected in all genetic groups, with higher occurrence in the and Marota race. Positive samples for Mmcluster were only observed in Moxotó (18.28%), Parda Sertaneja (1.92%) and SPRD (3.12%) rats. In the study of association between positivity and milk composition, a statistical difference was observed for protein, casein and somatic cell counts. The detection of Mycoplasma in samples of goat milk suggests the introduction of infected animals in the evaluated herds, as well as the possible contact with the etiological agents in fairs and exhibitions. In addition, the breeding system adopted on the property influences the spread of the infection in the herd. For the execution of Experiment 2, a total of 181 female goats of different races from the state of Pernambuco and Paraiba were selected. Milk samples were harvested and extracted from genomic DNA as described in Experiment 1. The genotyping of the animals for the 285bp fragment of the GoLA-DRB.2 gene was the result of amplification by PCR-RFLP technique, using the enzymes of Restriction PstI and TaqI. The allelic frequency found for the total population using the PstI enzyme was A equal to 0.7254 and B at 0.2746, with the frequencies of the AA, AB and BB genotypes being 0.6740, 0.0387 and 0, 2873 respectively. The allele frequencies obtained from the digestion with the TaqI enzyme were C = 0.8149 and D = 0.1851, with the frequencies of the genotypes: 0.7403 (CC), 0.1492 (CD) and 0.1105 ( DD), with predominance of the CC genotype in all the racial standards evaluated. The observed Heterozygosity values were lower than those found for expected Heterozygosity in all tested populations with herds out of Hardy-Weinberg equilibrium. There was significant genetic variation between races, among individuals of the same race and within the population. There was no significant difference between genotypes and haplotype patterns on the values of fat, protein, lactose, total solids, casein and somatic cell counts. The GoLA-DRB.2 gene was polymorphic in the evaluation with the PstI and TaqI enzymes studied but had no effect on any of the somatic cell composition and counting characteristics evaluated.