Incidência do primeiro molar em cavalos Crioulos e sua correlação com a genética

Abstract

The placement values in high functional performance animals and high value livestock, made the breeding of these individuals wascarried out in high scale, focusing often the same lineages in order to accelerate the improvement and enhance their products. So, inbreeding is a reality within the creations. In addition, there was the modification of natural horse eating habits, substantially altering the pattern of chewing. With this, the most varied dental disorders started to have an influence in the performance. Equine dentistry is not included in the selection criteria of animals for reproduction, mainly due to lack of studies correlating dental abnormalities with genealogy and athletic performance. However, this is very important, as it will guide the breeder to avoid undesirable effects of inbreeding. Among the dental abnormalities wolf tooth or premolar 1 (PM1) is the most frequent. On this basis, this study aimed to assess the impact of PM1 and identify the factors contributing to the variation in a sample of 443 horses, male and female of the Criollo breed examined clinically, between the years 2013 and 2014. Two hundred and twenty three out of 443 animals, (approximately 50.34%), showed the first premolar. Assessments using chi-square (χ2) did not identify any significant association (P = 0.4648) between sex and the presence of the first premolar. The percentages of occurrence in accordance with the position 105, 205 and both (105-205) were, respectively 6.32%, 7.00% and 37.02%. There was a significant association (P <0.0001) between the age of the animal (groups 1-3) and the presence of wolf tooth. The highest frequency of wolf tooth wasobserved in animals from group I (age 1-3 years) and the lowest in animals of group III (above 10 years). There was also a significant association (P=0.0004) between lineages (Brazilian, Uruguayan and Chilean) and the presence of wolf tooth. The highest incidence of wolf tooth occurred in the Uruguayan lineage (66.67%) and the lowest in the Brazilian strain (46.35%). Inbreeding evaluated in the study population ranged from 0.0 to 0.2812. The average inbreeding (standard error) in males was 0.015 (0.026) and females 0.009 (0.021). The inbreeding among animals with and without wolf tooth were 0.011 (0.025) and 0.015 (0.024) respectively. The mean and standard errors from inbreeding coefficientin accordance with age groups (I, II and III) were 0.016 (0.021) 0.014 (0.027) and 0.007(0.019), respectively. The mean and standard deviation of consanguinity according to the lineages (Brazilian, Chilean and Uruguayan) were 0.009 (0.019) 0.011 (0.012) and 0.023 (0.032), respectively. Fifty out of 443 animals were selected for genetic analysis, 25 with the presence of wolf tooth and 25 without this change. Genomic DNA was extracted from whole blood and checked on 1% agarose gel. These 50 samples were subjected to SSCP analysis and sequencing to check polymorphism in the first exon of the gene MSX1. Although no causal relationship has been established between exon I of MSX1 gene and the presence of wolf tooth, this is the first attempt to relate this kind of change and homeobox gene in horses. We can conclude from this study that there is a strong relationship between wolf tooth with age and lineage, but there is no influence of gender on this dental anomaly. A large genetic influence also exists because there is a stronger expression (occurrence) of this anomaly in the upper dental arch. Speculatively,we can say that these associations observed in this study are partly due to inbrreding levels presented by the evaluated animals.