Effect of increased milking frequency in early lactation with or without recombinant bovine somatotropin

Multiparous Holstein cows ( n = 300) were assigned to 1 of 2 milking frequency treatments at parturition. Cows were either milked 6 times ( 6 x) or 3 times ( 3 x) daily to determine effects on early lactation milk yields and subsequent lactation persistency with or without use of recombinant bST (rbST). Treatments included a control group milked 3 x and 3 groups milked 6 x for either the first 7, 14, or 21 days in milk ( DIM). Those 4 groups of cows all received rbST starting at 63 DIM. The fifth treatment group was also milked 6 x for the first 21 DIM but those cows received no rbST during the entire lactation. All cows returned to 3 x milking after their respective treatment periods ended. Cows milked 3 x tended to produce more milk (43.2 vs. 41.5 and 41.0 +/- 1.1 kg/d) during the first 9 wk of lactation compared with cows milked 6 x for 7 or 21 DIM, respectively. Group milk yields after wk 9 averaged 38.3 +/- 0.7 kg/d and did not differ among various groups assigned to an increased milking frequency in early lactation. Percentages of milk fat (3.8 +/- 0.12%) and protein (2.9 +/- 0.06%) did not differ among treatments during the first 9 wk after calving. Early lactation milk yield (41.9 +/- 1.2 kg/d) did not differ between the 2 groups of cows milked 6 x for 21 DIM. However, cows subsequently administered rbST ( at 63 DIM) produced more milk (38.8 vs. 34.2 +/- 0.9 kg/d) from wk 10 to 44. The number of cows sent to the hospital during the 305-d trial for mastitis ( 97), digestive disorders ( 14), respiratory issues ( 9), lameness ( 22), or retained placenta ( 16), were not affected by treatments (chi(2) = 0.49). Under the conditions of this commercial dairy herd in Arizona, increasing milking frequency to 6 times daily for 7 to 21 d at the start of lactation conditions did not increase milk yield nor improve lactation persistency.