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Table 3 Overview of the explanatory variables (n = 12) included in the observational study

From: The effect of age when group housed and other management factors on playing and non-nutritive sucking behaviour in dairy calves: a cross sectional observational study

Population conditions Explanatory variables
Quantitative data = Q
Qualitative data = q;
q1 nominal and q2 dichotomised
Individual level Age when grouped (Q) The decisive age for when calves are housed with other calves for the first time (days)
Sex (q2) Whether calves were heifer calves (h) or bull calves (b)
Sickness (q2) Whether any calf was sick or had been treated after birth (yes or no)
Space per calf (Q) The space in the pen per calf (m2)
Age when filmed (Q) The individual age of each calf in every calf-group (days)
Group level Indoor- or outdoor rearing (q2) If calves were placed indoors (i) or outdoors (o)
Group size (Q) The number of calves grouped together (number)
Regrouping (q2) Whether calves had been removed or released from the groups (yes or no)
Conventional / organic farm (q2) If the calf-group came from an organic farm (o) or a conventional farm (c)
Age difference in group (Q) The calculated age difference between the youngest and oldest calves in the group (days)
Milk allocation method (q1) What type of feeding system the calves get their milk allocated in: bowl, trough, robot, or drinker buckets with teat
Accessibility to dry teats (q2) Whether calves had dry teats in their pen (yes or no)
  1. Of the 12 explanatory variables, five were recorded at the individual level and seven at the group level. Of the qualitative data (q), only milk allocation method was treated as nominal (q1), while six others were dichotomised (q2) for analyses