Endogamia e caracterização da estrutura populacional da raça bovina Shorthorn e ovina Romney Marsh

Abstract

The present study is the result of the necessity to characterize the genetic structure through the study of the pedigrees of two farm animal species raised in the Rio Grande do Sul state. Data used for the study of the Shorthorn cattle breed were provided by the Associação Brasileira de Criadores Herd Book Collares and data from the Romney Marsh breed were provided by Associação Brasileira de Criadores de Ovinos. Complete data from cattle born between 1906 and 2018 were used, with a total of 29,723 records, and sheep born between 1980 and 2018, with a total of 17,053 records. For inbreeding analyses SAS software was performed, for additional demographic parameters analyses was performed with ENDOG software. Pedigree knowledge of Shorthorn cattle show enough completeness for a robust analysis. The mean inbreeding coefficient of the bovine population born within the 112-year recording interval was 1.91%, and the mean inbreeding coefficient of the sheep population over the 38-year period was 3.55%. The mean inbreeding coefficient of the cattle and sheep inbred animals was 9.08% and 10.31%, respectively. The inbred Shorthorn population in Brazil is 18.34%, and the inbred Romney Marsh population is 34.48%. The parameters of increases inbreeding rate by maximum, complete and equivalent generation for the Shorthorn breed were 0.16%, 1.91% and 2.60%, respectively. The same parameters for the Romney Marsh breed were respectively 1,02%, 1,50% and 2,23%. The number of ancestors explaining 50% of the gene pool in the Shorthorn population was 121, and Romney Marsh was 16. The average interval of generations found in the present study for the Shorthorn population was 6.14 years, and for the Romney population Marsh was 4.04 years. Levels of inbreeding are low in the Shorthorn breed not representing a major concern, and intermediate levels within the Romney Marsh population. Genetic bottlenecks are present in the pedigrees indicating loss of genetic diversity in both breeds. The drastic decrease in the number of Shorthorn breeders is worrisome. Romney Marsh show his main 10 problem in the lack of genetic material to be used for genetic outcross. It is recommended that Brazilian breeders of both breeds use sires of wide genetic variety to maintain the genetic health of both breeds.