There are reel mixers, three and four auger horizontal mixers and vertical mixers. All designs are a series of compromises and each has its advantages. Some mixers are true TMR (Total Mix Ration) mixers. Because of the poor mix quality of some mixers, a new term is being used to describe them; PMR or Partial Mix Ration mixers.
When recently talking to Dr. Tom Oelberg from Diamond V, he knew of two studies that verified the importance of mix quality. One was a study from 2011 to 2012 in eastern Ontario, Canada, where 22 farms were visited during the summer and winter. The results were part of a larger study investigating the relationship between feed sorting, feeding management and productivity measures of freestall housed dairy cows.
The conclusion is that measures taken to improve TMR composition, in relation to daily variability, may lead to improvements in DMI, milk yield, and efficiency of group housed dairy cows, ultimately increasing herd profitability. (Source: Sova et al. 2014 J. Dairy Sci 97:562-571)
Another source is from a Diamond V research study. It shows that mixes with CV of under 2% had higher milk and energy corrected milk production, with similar dry matter intake, compared to rations with a CV of 4.6% and 5.4 %
We do have a history of producers that switched types of mixers for a short period of time and have increased production. When their old mixers were returned, production went back down. When these same producers traded in their old mixers, their production went back up.
Is mix quality important? Yes; it is very important. Even a 2-lb. increase per day represents an increase of $900 per month, for every 100 cows at $15 milk.