Changes in milk production in response to IMF. A. Total milk yield or B. difference in milk yield between udder halves, of 6 cows assigned to unilateral frequent milking (UFM; twice daily milking (2×) of the left udder half, four times daily milking (4×) of the right udder half) for days 1 to 21 of lactation. Quartermilk production was measured through 45 d of lactation, and milk production from the 2× udder half was subtracted from that of the 4× udder half to obtain differential yield. There was no difference between udder halves in milk production on day 1 of lactation (P > 0.30). Milk production of the 4× udder half increased dramatically (P < 0.001) during UFM and was greater than that of the 2× udder half through day 45 of lactation (P < 0.01). Black vertical arrows indicate timing of biopsy sampling.