It is well known that milking frequency affects milk production. A review paper by Dr. Mark Varner at the University of Maryland estimated an average 12% response in milk yield from 3x vs. 2x milking, and an additional 8% response from 4x vs. 3x. Of course, these are averages and the actual response varies from farm to farm. Production responses to milking frequency do not come without additional costs. Cows have to be moved through the milking center more frequently, and one milking is unavoidably in the middle of the night. The extra labor equipment and utility costs can be significant, and the additional stress on the management is an important reason that many farms abandon or never use increased milking frequencies. Recently, research done predominantly by Dr. Geoffrey Dahl at the University of Illinois has shown that increasing milking frequency during the first 21 days of lactation results in a persistent increase in milk yield that continues after treatment has ceased. This seems like a free lunch! Imagine, one only has to increase milking frequency in the first three weeks of lactation to reap the benefits the rest of the year. Recent research presented at the joint annual meeting in St. Louis should reduce our expectations somewhat.
In a first trial reported by Matt Von Baale at the University of Arizona, two hundred multiparous cows were randomly assigned to one of five milking frequencies at calving to investigate the effect of increased milking frequency on milk yield with and without bST. Treatments were 6x milking for 0 (control; milked 3x), 7, 14, or 21 days in milk (with bST initiated at 9 weeks of lactation), or 6x for the first 21 days of lactation but without bST for the entire lactation. So far, only the data for the first 63 days of lactation have been summarized. Treatment effects on milk yield were small and not significant (90.8, 87.7, 91.5, 86.2, and 90.4 LB/day, respectively). Treatments did not affect milk fat (average 3.80%), true protein (average 2.80%), and somatic cell count (average 220,000 cells/ml).
The second study was conducted at Cornell University and reported by J. Fernandey. One hundred and five Holstein cows entering second or greater lactation were assigned at calving to either a control (2x milking during the entire lactation) or an increased milking frequency treatment (4x milking at 5 to 7 hour intervals from day 1 to 21 post calving, followed by 2x milking for the rest of the lactation). For the first nine months of lactation, cows milked 4x during the first 21 days had a 4.6% greater milk yield (78.l vs. 74.7 LB/day) compared to the cows milked 2x but also had a lower milk fat (3.37 vs. 3.52%) and milk true protein (2.83 vs. 2.93%) such that yields of milk fat (2.65 vs. 2.65 LB/day); 3.5% fat-corrected milk (77.6 vs. 75.4 LB/day), and true protein (2.23 vs. 2.20 LB/day) were not affected by treatments.
Based on these results and those of previous experiments, it appears that management and nutrition factors may modulate the response to milking frequency. For example, it has been suggested that holding times (time elapsed between the exit time and the return time for the last cow in a pen) in excess of 150 minutes/day negatively affects milk production. Many facilities designed to milk a pen of cows in 75 minutes twice a day cannot milk a fresh cow pen four times a day in less than 40 minutes per milking. Under these conditions, it is possible that the gain from the increased milking frequency is negated by the loss from excessive holding time.
There are other trials underway at university and commercial herds. These and other results will be reviewed by Dr. Geoff Dahl during our next Ohio Dairy Management Conference, December 2 and 3, 2004.