Side preference of dairy cows in the milking parlour and its effects on behaviour and heart rate during milking

Abstract

Side preference of dairy cows in a two-sided milking parlour was studied under practical and experimental conditions. Historical data, originating from the computerized identification of cows over a period of 28 months, revealed that 23 out of 89 cows showed significant ( P < 0.05) left-side preference in more than 75% of their lactation months. Twelve of these cows showed this side preference in all months. For the right side of the parlour, these numbers were 20 and 11, respectively. Two groups of eight cows, showing either significant or no side preference, were selected. These cows were individually tested for parlour side preference during 18 successive milkings. Test outcomes confirmed historical results for all but one cow. By milking the eight individual cows showing side preference alternately on both their habitual side (H-cows) and their nonhabitual side (N-cows), effects of side preference on behaviour, heart rate and milk production were examined in six successive afternoon milking sessions. The order of testing as well as the side of the parlour on which each animal was milked was alternated on a daily basis. Eight cows not showing side preference acted as controls (C-cows). N-cows used significantly more ( P < 0.05) time to enter the milking parlour (86 s) than H-cows (20 s) and C-cows (31 s). When feeding during milking, N-cows paused significantly more ( P < 0.05) often (0.89 times per min) in contrast to H-cows (0.49) and C-cows (0.51). During the first minute of milking, the increase in heart rate as well as heart rate variability was significantly higher ( P < 0.05) in N-cows (21.8% and 3.2, respectively) than in H-cows (16.7% and 2.0). No differences in milk production between treatment groups could be detected. From this study, it can be concluded that: 1) individual cows differ consistently in side preference in the milking parlour; 2) a substantial proportion of the cows showed consistent side preference in spite of changes in their social environment or in other environmental factors; 3) side preference of dairy cows in the milking parlour seems to be a consistent behavioural routine with only unimportant implications for the welfare of cows if it were to be interrupted.