effect of milking frequency on the lactation performance and lactation curve of holstein dairy cows in iran

the aim of this study was to investigate the effect of milking frequency (three times daily vs. two times daily) on the lactation curve shape, partial and 305-d lactation performance in holstein dairy cows in iran. data from february 2000 to december 2012 comprising 217345 lactations on 141364 cows distributed in 324 herds collected by the animal breeding center of iran were used. the mean milking frequency was 2.88 (0.32) times and increased from 2.72 (0.004) times in 2000 to 2.97 (0.002) times in 2012. the shape of the lactation curve for cows milked thrice daily tended to be higher and flatter than that for those milked twice. the first parity cows milked twice daily had a significant lower days in milk (dim) until peak (79.52 (0.49) days) than those milked thrice (88.66 (0.28) days). in all parities except for parity ≥ 4, lactation persistency was higher in the cows milked thrice daily than in those milked twice. the percentages of increase in 305-d milk yield due to increasing milking frequency from two times to three times daily, were 12.34, 14.02, 12.79 and 14.76% for cows in parity 1 to parity ≥ 4, respectively. the 305-d milk yield was higher by 959 (28.89), 1175 (32.7), 1099 (38.6) and 1271 (45.0) kg for cows milked thrice daily than those milked twice in parity 1 to parity ≥ 4, respectively. the corresponding values for the 305-d fat yield were 4.35 (0.98), 16.68 (1.11), 17.19 (1.28) and 18.76 (1.51) kg. based on the results of this study, it can be concluded that increasing milking frequency not only increased milk yield but also improved the initial yield, peak yield and lactation persistency.