Análise genética de vacas em relação à sua idade no último parto através de modelos de sobrevivência

Abstract

In Brazil, the study of bovine longevity is extremely important due to the country’s position in the export and production of this sector and, for this reason, there is a strong interest in achieving maximum profitability in this activity. The economic longevity of cows is totally related to reproductive performance, with the trait known as the age of the cow at last calving (ACLC) being a very important variable in this context. Since this variable cannot always be perfectly measured in some scenarios, a censoring criterion is generally applied to this characteristic, which is based on the difference between the date of the cow’s last observed calving and the date of the last calving on the farm. If this difference is greater than or equal to 36 months, the cow failed, as she has gone too long without calving and will be discarded. Otherwise, the cow is still considered reproductive and her age at last calving is censored, since there is still a possibility of her having another pregnancy. Therefore, one of the objectives of this study is to genetically analyze the IVUP variable using frailty models applied to survival analysis. The use of this type of model is justified by the inclusion of random effects, allowing the prediction of genetic factors associated with each animal and also considering associations between them. Another objective of the study is to identify genetic variables that influence bovine longevity, and this will be done through a Genome-Wide Association Study (GWAS). The analysis is done using a sample of 862 cows, daughters of 47 different bulls. For confidentiality reasons, the origin of the data is kept secret.