Evaluation of test duration for feed efficiency in growing beef cattle.

Abstract

The aim of this study was to determine the shortest test duration necessary for the evaluation of feed efficiency traits, i.e., dry matter intake (DMI), average daily gain (ADG), mid-test metabolic body weight, residual feed intake (RFI), feed conversion ratio (DMI/ADG), and feed conversion efficiency (ADG/DMI). A total of 313 Nellore bulls with an initial age of 283 ± 23.6days were evaluated by automated feed intake measurement. The tests were divided into six durations (15, 29, 43, 57, 71, and 84days), with at least one body weight recording at the beginning and one at the end of each period. Residual variances were estimated per period and correlation coefficients (Pearson and Spearman) were calculated between the 5 test durations and the 84-day test. The results indicated a minimum test duration of 15days (two weight recordings without fasting) for the measurement of mid-test metabolic body weight, a minimum of 43days for automated DMI measurement, and a minimum of 71days for the determination of ADG, RFI, feed conversion ratio, and feed conversion efficiency. Individual analysis of the DMI records obtained with the GrowSafe® and Intergado® automated feeders showed that a test duration of 57days is sufficient for measurement of this trait. We therefore recommend a test duration of 71days after a minimum adaptation period of 21days for the determination of feed efficiency in growing Nellore cattle, with weight recordings without fasting every 15days.