Optimal timing and duration of unilateral frequent milking during early lactation of dairy cows.

Increased milking frequency during early lactation can elicit immediate and persistent increases in milk yield; however, the timing and duration of frequent milking have not been optimized. Our objective was to use a half-udder model to determine the milk yield response to 2 wk of frequent milking imposed at 2 different times in early lactation. Multiparous Holstein cows were assigned at parturition to unilateral frequent milking [UFM; twice-daily milking (2x) of the left udder half and 4-times-daily milking (4x) of the right udder half] on d 1 to 14 (UFM-1-14) or 7 to 21 (UFM-7-21) of lactation (n = 10 cows per treatment). Cows were milked 2x before and after UFM. Half-udder milk weights were measured at 1, 3, 7, 14, 21, 28, and 35 d in milk, and then once every 3 mo for the remainder of lactation. For both treatments, the 4x udder halves produced more milk than the 2x udder halves during UFM, resulting in an average difference of 3.7 +/- 0.7 kg/d in UFM-1-14 cows and 2.9 +/- 0.9 kg/d in UFM-7-21 cows. After cessation of UFM, milk production of the 4x udder halves decreased in both treatments, but UFM-7-21 cows produced 1.5 +/- 0.6 kg/d more milk from the 4x side than the 2x side for the remainder of the lactation. In UFM-1-14 cows, the difference was 1.2 +/- 0.7 kg/d, which was significant overall, but not at 270 d in milk. In both treatments, the full-lactation yield of the 4x udder half was greater than the 2x half. Moreover, the total milk yield response to UFM observed in the current study did not differ from that observed in a previous study in which cows were assigned to UFM from d 1 to 21 of lactation. We conclude that UFM for a 2-wk interval during early lactation elicited a persistent increase in milk production of the frequently milked udder half. In addition, the overall milk yield responses observed for UFM-1-14 or UFM-7-21 were not significantly different than that previously observed for UFM on d 1 to 21 of lactation.