The objective of this work was to determine the population structure and the effects caused by inbreeding in a closed herd of Nellore cattle of the Lemgruber line. The pedigree file included records of 39,290 animal, 17,646 males and 21,644 females, born between 1951 and 2007. The population structure was analysed using the software Poprep and Endog, which resulted in some level of inbreeding for 61,82% of the animals. The average F value was 3.02% for the whole population and 4.89% for the inbred animals; and F maximum value was 37.5%. The number of ancestors that contributed to the reference population was 2,380 animals, from which only seven explained 50% of the genetic variability of the population. The effective number of founders (Nf) and the effective number of ancestors (Na) in this population were, respectively, 25 and 21. The expected increase of inbreeding, caused by the unbalanced contribution of founders, was 1.62%. The herd populational structure shows the aging of the breeders, with a consequent increase of the generation´s interval, as well as a continuous increase of inbreeding and a high percentage of inbred individuals. Such facts compromise the annual genetic gain and should deserve a closer attention from breeders.
inbreeding; Nellore Lemgruber; effective population size; genetic variability
