Influência do período de teste na mensuração do ganho médio diário para fins de avaliação genética de características de eficiência alimentar em bovinos nelore

Abstract

The objective of this work was to evaluate the influence of the test period on the measurement of the average daily gain (ADG), used in the prediction of residual feed intake (RFI), for genetic evaluation on feed efficiency of Nelore cattle. The experiment was carried out at the Federal University of Uberlândia (UFU), at Capim Branco Experimental Farm, located in Uberlândia, MG. Twenty-seven Nelore animals were used, all male, born in 2017, with an average initial age of 18 ± 0.91 months, coming from 13 different farms. The studied food efficiency variables were: average daily gain (ADG; kg/day) and residual food intake (RFI; kg/day). The ADG was estimated as the linear regression coefficient of the weights as a function of the days under test. RFI was calculated as the difference between the observed DMI and the expected DMI. Seven evaluation scenarios were considered in the prediction of ADG and RFI: 70-day test period with daily weighing (REF); 49-day trial period with daily weighings (A); 42-day trial period with daily weighing (B); 35-day trial period with daily weighing (C); 56-day trial period with weekly weighings (D); 70-day trial period with weighing at 14-day intervals (E); 56-day trial period with weighings at 14-day intervals (F). Spearman correlation was used to verify the classification of the animals in the different scenarios in relation to the REF scenario. Scenario E obtained the highest Spearman correlation (0.95) in relation to the REF scenario, that is, 90% of the animals classified for ADG did not show alteration in the ranking. The second best proposal for the test period was scenario D, where a Spearman correlation coefficient of 0.93 was obtained. The largest changes in animal classification were found in scenarios B and C, where only 71% of animals maintained the same ranking obtained in the REF scenario for ADG. Scenarios A, D and E showed the lowest alteration in the ranking of animals, with Spearman correlation coefficient close to one (0.98), that is, 96% of the animals did not change the classification of RFI in reference scenario comparison (REF). From the evaluated scenarios, it can be concluded that the test period for gross feed efficiency (GFE) evaluation with higher reliability in predicting ADG and RFI phenotypes is 70 days with weighing at 14 days intervals. However, the GFE testing period may be reduced to 56 days if weekly weighing is performed. If daily weighing is possible, the test period can be reduced to 49 days without affecting the reliability of ADG and RFI predictions in Nelore cattle.