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A field study was conducted on two commercial dairy production units to determine the effects of milking Holstein heifers prepartum on prepartum mastitis, reproduction, milk production, and overall health. Holstein heifers were assigned at least 30 days prior to the expected date of parturition to one of three treatment groups: Non-Prepartum Milked Control, Postpartum Milked (C; Farm 1, n = 31; Farm 2, n = 15), Prepartum Milked (P; Farm 1, n = 68; Farm 2, n = 16); and Prepartum Milked with Mastitis (M; Farm 1, n = 27; Farm 2, n = 4). Prepartum milking consisted of twice daily milk removal by machine milking. The number of days milked prepartum depended upon fullness of the teats, detection of milk leakage, and any visual indications of mastitis. Days milked prepartum ranged from 1 to 144 days. The incidence of prepartum mastitis was 21% on farm 1 and 20% on farm 2. Heifers with clinical mastitis prepartum were treated with an intramammary antibiotic for lactating cows. Average daily prepartum milk production, days milked prepartum, and total prepartum milk production were influenced by season. Average daily milk production and number of days milked prepartum were greatest (p < 0.0001) for heifers that initiated lactation in the spring and summer compared to fall and winter. Prepartum and postpartum mastitis were associated with teat end shape and viscosity of initial prepartum milk secretion. Heifers with flat teat ends had a greater incidence of mastitis prepartum compared to those with round shaped teat ends. Postpartum milk production was greatest for prepartum milked heifers (M and P) compared to C for first lactation. Postpartum linear somatic cell scores did not differ among groups, but were affected by season. There was no difference in the number of days to first service among groups, however M heifers had the greatest number of services per conception (p < 0.0001), days open (p < 0.0001), and longest calving interval (p < 0.0001). Initiating milking when fullness of the teats appear large enough to support a milking unit and before edema and congestion of the udder occurs may prove beneficial for improving udder health, reproduction, and overall health during the first lactation.