Effects of increased milking frequency during early lactation on milk yield and udder health of primiparous Holstein heifers.

In dairy cows, increased milking frequency (IMF) during early lactation stimulates an increase in milk yield that partially persists through the remainder of lactation. However, the effects of IMF on lactation performance and udder health of primiparous heifers have not been clearly established. The objective of this study was to determine the effects of IMF during early lactation on milk yield and composition, udder edema, and teat-end condition of primiparous Holstein heifers. Thirteen heifers were assigned at parturition to unilateral frequent milking (twice-daily milking of the left udder half (2X), and 4-times-daily milking of the right udder half (4X)) from d 1 to 21 of lactation. Heifers were milked twice daily at 0130 and 1330 h, with additional milking of the right udder half at 0430 and 1630 h. Half-udder milk yield and composition were recorded on d 1 and 4, weekly through 35 d in milk (DIM), monthly through 210 DIM, and on d 270±1 of lactation. Udder edema and teat-end scores were evaluated on d 1 and 4, weekly through d 35, and on d 60±1 of lactation. A 1-sided paired t test was used to compare milk yield of 4X- to 2X-udder halves. A 2-sided paired t test was used to test for differences in milk composition, udder edema, and teat-end scores. Overall, 4X stimulated an immediate increase in milk yield. Differential milk yield peaked on d 21 of lactation, with 4X udder halves producing 2.8 kg/d more milk than 2X udder halves (P<0.001). After cessation of 4X, the milk yield differential decreased, but 4X udder halves continued to produce 0.8 kg/d more milk than 2X udder halves through d 270 of lactation (P<0.05). Over the entire lactation, milk component yields and 3.5% fat-corrected milk or energy-corrected milk were greater (P<0.05), whereas somatic cell counts in milk were lower, in 4X udder halves (P<0.05). Udder edema and teat-end condition did not differ between 4X and 2X (P>0.19). In conclusion, IMF during early lactation stimulated a persistent increase in milk yield without negatively affecting several indicators of udder health of primiparous dairy heifers.