Udder health of cows changing from tie stalls or free stalls with conventional milking to free stalls with either conventional or automatic milking.

Udder health and milk production were monitored in cows transferred from tie stalls or loose housing with conventional milking to loose housing with either automatic or conventional milking. Data were collected from 182 Finnish farms from September 1999 to February 2006. Data from the first year before and first year after the changes were compared. A total of 88 herds changed from conventional milking (CM herds) to automatic milking (AM herds), 29 of which were housed in tie stalls and 59 of which were housed in a loose housing barn before the change. Additionally, 94 CM herds milked in loose housing barns that had been housed in tie stalls before the change were included. Milk record data consisted of annual herd size, parity, breed, calving dates, test day data [date, milk yield, and cow somatic cell count (SCC)] and records for treatments of clinical mastitis. Calculations were made for energy-corrected milk yield and logarithmic SCC (logSCC), proportion of cows at risk that experienced an SCC >200,000 cells/mL for the first time (highSCC), and number of treatments of clinical mastitis within a herd. Cows in tie stalls had higher milk yield (28.5 +/- 0.29 vs. 26.5 +/- 0.46 kg/d) and a lower logSCC (4.86 +/- 0.01 vs. 4.95 +/- 0.02) than cows in loose housing barns before the change. After the change, CM herds had slightly better udder health than AM herds because the proportion of cows at risk for highSCC was larger in AM herds (3.3 vs. 2.1%). The change in milking and housing systems caused a decline of 0.8 +/- 0.25 kg/d per cow in energy-corrected milk yield, a slight increase in cow logSCC (from 4.88 +/- 0.01 to 4.93 +/- 0.01), and an increase of 0.6% in the proportion of cows having highSCC (from 2.5 to 3.1). The impact was clearer on herds that began automatic milking. Based on the results, the increase in bulk milk SCC of herds milked automatically in Finland was probably due to reduced separation of mastitic milk in AM herds.