Milking frequency as related to udder health and milk production

Twenty-four cows each in two trials were paired on age, stage of lactation, and projected milk production to compare the incidence of mastitis with milking two or three times per day over 12 wk. Teats of all cows were dipped daily in a suspension of Streptococcus agalactiae (one of two strains). Average daily milk production for the combined trials was 24.0 kg for the thrice daily group and 22.0 kg for the twice daily group. Quarter foremilk samples were taken every 2 wk for somatic cell counts and bacterial isolations. Somatic cell counts of cows milked twice per day averaged 31 x 10(3) per milliliter compared to 26 x 10(3) for three milkings. There were no significant differences in numbers of new bacterial infections between groups. Cows milked twice per day had 41 new infections and 7 clinical infections and the three-time group had 39 new infections and 2 clinical infections. The many corynebacteria infections were related to the experimental design in which no disinfectant teat dip was used. Three milkings per day did not affect udder health.