Effect of low light intensity at night on cow traffic in automatic milking systems

Several studies have shown benefits of long-day (16 h) photoperiod in lactating dairy cows, but have not identified a suitable light intensity for the dark hours. It is known that the locomotion pattern of dairy cows is altered at low light intensities and this may translate to reduced cow traffic and milking frequency, which would have a negative impact on system productivity. However, it is also recognised that a significant disturbance of rest may have a negative impact on the health and productivity of high-yielding dairy cows. This study examined the effect of three different night-time light intensities (LOW: 11 ± 3, MED: 33 ± 1 and HIGH: 74 ± 6 lx) on number of gate passages, milking frequency and milk yield in dairy cows in automatic milking systems. The study was conducted in Sweden during the winter of 2012-13 and the treatments were applied in a crossover design to three herds with an automatic milking system. Minimum day time light intensity was 158 lx. Data on gate passages, milking frequency and milk yield for 172 ± 49 (mean ± s.d.) cows during the last 22 days of each 34-day study period were analysed for treatment differences and differences in daily distribution over 24 h, during day time and night time. Light intensity did not affect total number of gate passages per 24-h period and cow, but number of gate passages per hour and cow was in all treatments lower during night time than during day time. Milking frequency was increased in MED compared with both HIGH and LOW (P < 0.05). Milk yield decreased with reduced light intensity, and differed significantly between HIGH and LOW treatments, 45 ± 1 kg and 44 ± 1 kg, respectively (P < 0.001). Our conclusion is that reducing light intensity to 11 lx at night time does not affect cows' general activity as gate passages remained the same for all treatments. However, milk yield decreased with reduced light intensity, which might be related to a lower feed intake. We argue that providing night light for dairy cows, as required by many welfare acts, might be related to production level rather than welfare aspects and that the recommendations should be revised. © CSIRO 2014.