Arena behaviour of Merino weaners is heritable and affected by divergent selection for number of lambs weaned per ewe mated

•Arena behaviour was studied in a flock divergently selected for lambs weaned per ewe mated (H and L lines respectively).•H line weaners showed behaviour suggestive of lower stress levels to a stationary human during flock isolation.•All arena traits were heritable and variable and should respond to selection.•Analyses of breeding values from the flock suggested that H line weaner were also less stressed on a genetic level.•Lower levels of fear during in farmed ovine livestock is desirable for improved animal welfare. Data of 3375 6.5-month-old Merino weaners from two divergently selected lines at Elsenburg were used to evaluate the genetics of the response of weaner lambs to flock isolation and a stationary human in an arena test. The High (H) line was selected upwards and the Low (L) line was selected downwards for number of lambs weaned per ewe mated (NLW) from 1986 to the present. Selection resulted in divergent lines for NLW, live weight up to yearling age, wrinkle scores as well as other breech strike indicator traits such as breech and crutch cover scores. Weaners from the H line (selected for NLW) travelled longer distances in the arena, based on the number of squares crossed. They also bleated at a lower frequency and urinated and defecated at a lower frequency than their L line contemporaries (all P < 0.05). The average distance the weaners maintained from the stationary human (0.10 ± 0.03), urinating events (0.15 ± 0.03), and defecating events (0.07 ± 0.02) were all lowly heritable. In contrast, the number of lines crossed (0.30 ± 0.04) and the number of bleats (0.38 ± 0.04) were moderately to highly heritable. Genetic correlations suggested that the weaners maintaining a larger distance from the stationary human covered a greater distance in the arena and were more likely to urinate during the test. Animals with a high urinating frequency were also likely to defecate more often. Genetic trends indicated that, over time, L line animals increased their distance from the human operator while they also bleated, urinated and defecated at a higher frequency. H line animals, in turn, exhibited fewer urination and defecation events over time. It was concluded that selection for NLW in the H line resulted in a range of behaviours that would indicate lower levels of stress when interacting with a stationary human in the arena. Animal welfare is facilitated by lower levels of stress as well as good animal-stockperson relations during unfamiliar procedures