Effect of Increased Milking Frequency in Early Lactation With or Without Recombinant Bovine Somatotropin

摘要

Multiparous Holstein cows (n = 300) were assigned to 1 of 2 milking frequency treatments at parturition. Cows were either milked 6 times (6x) or 3 times (3x) 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 3x and 3 groups milked 6x 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 6x for the first 21 DIM but those cows received no rbST during the entire lactation. All cows returned to 3x milking after their respective treatment periods ended. Cows milked 3x 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 6x 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 6x 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 (χ~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.