Effects of milking frequency in automatic milking systems on salivary cortisol, immunoglobulin A, somatic cell count and melatonin.

In barns with an automatic milking system (AMS), both the milking frequency and the number of nighttime milkings vary between cows. A low milking frequency might indicate problems in gaining access to the milking unit. Also, nighttime lighting in the waiting area of the AMS and in the milking unit increases exposure to light at night and could suppress nocturnal melatonin synthesis. These effects could result in increased stress, suppressed immune response, and poor udder health. A total of 125 cows (14-16/farm) on 8 farms with AMS were selected based on their average milking frequency. Eight to 10 saliva samples per cow were taken over the course of 4 days, and cortisol, IgA and melatonin concentrations were determined. Somatic cell counts (SCC) were determined in milk samples. Milking frequency had no significant relationship with mean cortisol and IgA levels, but a higher milking frequency tended to be associated with lower SCC levels. Nocturnal melatonin levels tended to be negatively associated with the number of nighttime milkings. In conclusion, no indication of increased stress or reduced immune defense was found in relation to milking frequency on farms with an AMS.