Aplicabilidade da eficiência alimentar no melhoramento animal de bovinos de corte

Abstract

Feed efficiency in beef production is essential for the sustainability of the sector, especially in Brazil, the third-largest producer and the second-largest exporter of beef worldwide. Residual Feed Intake (RFI) is a robust trait for evaluating this efficiency, as it allows the identification of animals that consume less feed without compromising growth and carcass quality. Thus, feed efficiency, assessed through RFI, is one of the main competitive factors in Brazilian beef cattle production. However, improving the methods for obtaining this trait to generate high-quality phenotypes and investigating RFI as a selection tool are fundamental strategies to enhance the accuracy of identifying more efficient animals. The first article of this thesis aimed to evaluate the influence of the test period on measuring average daily gain (ADG), used in predicting RFI, focusing on the genetic evaluation of feed efficiency in Nellore cattle. The second article estimated variance components, covariances, and genetic trends for RFI and dry matter intake (DMI) in Nellore cattle. In the first study, 27 Nellore males (initial average age of 18 ± 0.91 months) were evaluated at the Capim Branco Experimental Farm of the Federal University of Uberlândia. The ADG was estimated through linear regression of weights over the test period, and RFI was calculated as the difference between observed and expected dry matter intake. Seven scenarios with different test durations and weighing frequencies were analyzed, comparing the reliability of animal rankings to the standard scenario (REF). The results indicated that the 70-day test period, with weighings every 14 days (Scenario E), was the most reliable for feed efficiency evaluation, showing a 0.95 correlation between animal rankings. However, the test period can be reduced to 56 days if weekly weighings are conducted. The second article analyzed data from 7,808 animals evaluated in 142 feed efficiency trials conducted between 2011 and 2019, from farms participating in the Nelore Brasil program, coordinated by the National Association of Breeders and Researchers (ANCP). Variance components were estimated using the restricted maximum likelihood (REML) method. The heritability estimates for RFI and DMI were 0.22 and 0.28, respectively, suggesting a moderate response to selection. The genetic correlation between RFI and DMI was high and favorable (0.61), indicating that selecting for RFI will promote a reduction in dry matter intake. The results reinforce the importance of RFI as a selection criterion for feed efficiency in Nellore cattle. The most reliable test period for evaluating ADG and RFI is 70 days, with weighings every 14 days, but it can be reduced to 56 days with weekly weighings. No genetic trend was observed for RFI, whereas DMI showed a considerable increase over the evaluated period, with an annual genetic gain of 0.024 kg/day. These findings provide valuable insights for improving feed efficiency and the sustainability of Brazilian beef cattle production.