ABSTRACT.- The evaluation of sheep feed intake (FI) in feed efficiency tests is expensive. Decreasing the test period could be a resource-saving tool by reducing the cost of evaluating each animal and allowing to test a greater number of animals per year. For this reason, the objective of this research was to explore residual feed intake (RFI) models and to decreasing the test duration. Data was collected from 286 Australian Merino sheep of three performed trials, the test period consisted of 56 days (14 days of feed and facilities adaptation and 42 days of FI and average daily gain (ADG) evaluation). Two models were used to calculate RFI, Model 1 (based on Koch et al. (1963) linear model) and Model 2 (repeated measures, weekly model). Model 1 included ADG and FI estimates in a linear regression. The second model included weekly average FI as repeated measure and the weekly ADG. The increase in body weight during the test period was not perfectly linear, presenting a marked variance increase in two of the three tests while FI presented a tendency to increase throughout of the evaluation period, however presenting a high variance per day. In the 42-days tests, Pearson and Spearman correlations between models for ADG were of 0.89 and 0.87, respectively. The best correlations were detected for FI between 42 and 35-days models, presenting Pearson and Spearman correlations of 0.95 and 0.94 in the linear model, and 0.96 and 0.95 in the weekly model. When considering RFI, the correlations between linear and weekly 42-days models were from 0.93 to 0.92, respectively. The 35-days RFI length models (linear and weekly) presented a Pearson and Spearman correlations greater than 0.98 with the 42-days models. Therefore, the RFI models 35-days of duration allowed to decrease seven days of the FI test while maintaining accuracy and explaining 75.3% of the FI in the linear model, and 63.6% of the weekly model. Reducing seven days of testing would provide a greater data collection into a year of phenotypic evaluation. © 2022 The Authors. Published by Elsevier B.V.