Behavior during Human Approach- and Novel Object Tests and Associations with Performance from Barrows Selected for Residual Feed Intake

The extent to which selection for improved lean accretion and feed efficiency affects livestock behavior and response to stress is not well understood. The objective of this experiment was to examine the behavioral metric correlations and growth performance of barrows divergently selected for residual feed intake (RFI). Human approach- (HAT) and a novel object (NOT) test were employed to achieve the objective. Forty low- (LRFI, more feed efficient) and 40 high-RFI (HRFI, less feed efficient) barrows (46.5 ± 8.6 kg) from the 8^th generation Yorkshire selection lines were randomly selected and evaluated with HAT (an unfamiliar human) and NOT (an orange traffic cone) over four consecutive weeks. Each barrow was individually evaluated within a 4.9 × 2.4 m test arena for 10 min and frequency of escape attempts (from two legs off the ground, may include jump) and freezing (no movement for ≥3 s) were determined using video analysis. Performance measures were collected over the grow-finish period, and included ADG, feed conversion ratio, live weight, 10th-rib backfat-and loin eye area at the end of the finisher phase. Within lines, Pearson correlations were determined among performance and behavioral metrics during HAT and NOT with significant level set at P≤0.05. For HAT, escape and freeze frequencies were not correlated with performance measures for either line (P≥0.33). Within the LRFI line, freeze frequency during NOT was positively correlated with feed conversion ratio (r= 0.37; P=0.03). Escape and freeze frequencies did not have significant correlations with any other performance measures for either line during NOT (P≥0.07). In conclusion, freeze frequency was weakly correlated with feed conversion ratio in LRFI barrows during NOT, suggesting more feed efficient barrows freeze less in response to novel stimuli. Therefore, within the context of this genetic selection program for improved lean accretion and feed efficiency there were no negative behavioral effects during these fear tests.