Influence of fixed time artificial insemination in genetic values of economical traits for beef cattle

The fixed time artificial insemination (TAI) is an effective tool for genetic improvement of beef cattle, increasing dissemination of superior genetics and allowing artificial insemination in larger herds. The aim of this study was to compare the genetic values for weaning weight (WW), yearling weight (YW), scrotal circumference (SC) and muscularity (MUSC) traits after increase of artificial insemination (AI) and decrease of multiple reproducers (MR) in beef cattle herds in order to check the influence of TAI in animal breeding. The database was obtained from six farms participating of Nelore Qualitas Breeding Program. Records of 65,086 progenies of Nelore cattle were used. The season of birth was used to divide each farm in two groups. AI group was formed by progenies born from season that the percentage of AI reached 60%. MR group was formed by progenies born before this season. The genetic values of WW, YW, SC and MUSC were analyzed by least squares using the SAS software, considering the effect of group (AI and MR) in the models. Mean comparisons were analyzed by the Tukey-Kramer test (p <0.001). The group effect was significant in all analysis (p<0.001). For AI group, the estimated means of genetic values for WW, YW, SC and MUSC were 4.41 ? 0.04 kg, 7.19 ? 0.05 kg, 0.46 ? 0.01 cm, 0.25 ? 0.00 respectively. For MR group, the estimated means of genetic values for WW, YW, SC and MUSC were 1.31 ? 0.04 kg, 2.07 ? 0.06 kg, 0.16 ? 0.01 cm, 0.07 ? 0.00 respectively. Higher genetic values means were observed for progenies born from TAI, with differences between the studied groups of 3.1 kg and 5.1 kg for WW and YW traits respectively. The results of the present study imply that the TAI has positive influence on genetic values of beef cattle progenies for the studied economical traits as consequence it influences the performance of these animals at older age.