The objective of this experiment was to establish the effect of low-concentrate (LC) and high-concentrate (HC) supplementation in the early and late periods of lactation on milk production and cow traffic in a pasture-based automatic milking (AM) system. In total, 40 cows (10 primiparous and 30 multiparous) were randomly assigned to one of the two treatments. The experimental periods for the early and late lactation trials extended from 23 February to 12 April 2015 and 31 August to 18 October 2015, respectively (49 days in each trial period). The early lactation supplement levels were 2.3 and 4.4 kg/cow per day for LC and HC, respectively, whereas the late lactation supplement levels were 0.5 and 2.7 kg/cow per day for LC and HC, respectively. Variables measured included milking frequency, milking interval, milking outcome and milking characteristics, milk yield/visit and per day, wait time/visit and per day, return time/visit and the distribution of gate passes. As the herd was seasonal (spring) calving, the experimental periods could not run concurrently and as a result no statistical comparison between the periods was conducted. There was no significant effect of treatment in the early lactation period on any of the milk production, milking characteristics or cow traffic variables. However, treatment did significantly affect the distribution of gate passes, with the HC cows recording significantly more gate passes in the hours preceding the gate time change such as hours 7 (P<0.01), 15 (P<0.05), 20, 21 (P<0.001), and 22 (P<0.05), whereas the LC treatment recorded significantly more gate passes in the hours succeeding the gate time change, such as time points 2 (P<0.01) and 10 (P<0.05). There was a significant effect of treatment in late lactation, with HC having a greater milk yield (P<0.01), milking duration and activity/day (P<0.05), while also having a significantly shorter milking interval (P<0.05) and return time/visit (P<0.01). The distribution of gate passes were similar to the early lactation period, with HC also recording a significantly greater number of gate passes during the early morning period (P<0.01) when visitations were at their lowest. Any decision regarding the supplementing of dairy cows with concentrates needs to be examined from an economic perspective, to establish if the milk production and cow traffic benefits displayed in late lactation outweigh the cost of the concentrate; thereby ensuring that the decision to supplement is financially prudent.