The effect of selection for residual feed intake on scale-activity and scale-exit scores in Yorkshire gilts

Abstract

The objectives of the present study were to use scale-activity and scale-exit scores to (1) determine the extent to which selection for improved residual feed intake (RFI) correlates with individual gilt temperament, (2) determine whether the timing of assessment affects the scores, and (3) determine whether gilts habituate to the process of weighing. To achieve these objectives, 192 grow–finish purebred Yorkshire gilts (39.7 ± 5.7 kg; 98 ± 6 days old) were utilised. Ninety-six gilts were from the 5th generation of a line selected for low residual feed intake (LRFI), and 96 gilts were from the 5th generation of a randomly selected control line (CRFI). Gilt activity and exit behaviour were scored on the weigh scale. The activity score was taken at two time points, namely, t = 0 (immediately on the back gate closing on the weight scale) and t = 15 (15 s later). Activity was assessed using a 5-point scoring system (1 = calm, minimal movement; 5 = continuous rapid movement and an escape attempt), and exit score was assessed using a 3-point scoring system (1 = no encouragement needed, full exit; 3 = encouragement needed). Gilts were weighed once every 2 weeks (each weighing considered a testing round) for a maximum of eight scores per gilt. Statistical differences were identified in all rounds for activity between genetic lines, except Rounds 2, 4 and 5. For both lines, gilt-activity scores decreased over rounds. The LRFI line began with a lower activity score (2.31 vs 2.65 ± 0.13), but did not experience as great of a drop in average score over rounds as did the CRFI gilts (0.62 vs 1.21). By the end of the trial, the CRFI gilts scored lower than the LRFI gilts. Activity was greater at t = 15 than at t = 0. Although timing affected the score, the pattern was similar, and so consistency will be more important than timing procedure. For exit scores, in Rounds 5 and 7, the LRFI line scored lower than the CRFI line, and there was a trend for the LRFI line to score lower in Round 6. Across all gilts, the mean exit score increased slowly throughout the trial. In conclusion, selection for lower RFI in purebred Yorkshires has an effect on activity score but this relationship is complex and warrants further research. The observation that gilts become habituated to the process of weighing supports the conclusion that the process is not aversive.