The effects of incomplete milking and increased milking frequency on milk production rate and milk composition

摘要

Increased milking frequency and incomplete milking have differential effects on milk yield and mammary gland physiology that are important for optimization of milking practices in dairy herds. The objectives of this experiment were to determine the effects of increased milking frequency and incomplete milking on milk production rate (MPR) and milk composition and to determine if milking 3 times daily (3x) could rescue the negative production effects of incomplete milking. Twenty-two multiparous cows were enrolled onto this experiment beginning at 5 days in milk (DIM) and continuing through 47 DIM. A split-plot design was used to randomize the 2 treatments, which were milking frequency and incomplete milking. Eleven cows were randomly assigned to be milked 2 times (2x) daily and 11 cows were randomly assigned to be milked 3x. Within each cow, a contralateral half-udder was randomly assigned to be incompletely milked (30% milk remaining in the gland; IM), and the other half-udder was randomly assigned to be milked completely (CM). Quarter-level milk yields were recorded at each milking session. Milk samples from all quarters were collected twice weekly at the beginning of the morning milking for analysis. Cows milked 2x tended to have reduced MPR compared with 3x milked cows (1.81 +/- 0.06 vs. 1.97 +/- 0.06 kg milk/h; P = 0.06). Half-udders that were CM and IM produced 1.09 +/- 0.03 and 0.80 +/- 0.03 kg milk/h, respectively. There was an interaction between incomplete milking treatment and week of lactation (P = 0.04). No interaction was detected between milking frequency and incomplete milking for MPR or milk components. Cows milked 3x had increased milk fat percent (1.93 +/- 0.09% vs. 1.65 +/- 0.09%, P = 0.047), decreased milk lactose percent (4.80 +/- 0.04% vs. 4.93 +/- 0.04%, P = 0.04), and exhibited no differences in milk protein percent or milk somatic cell count (SCC) compared with cows milked 2x. Half-udders that were IM had increased milk fat percent (2.15 +/- 0.07% vs. 1.43 +/- 0.07%, P 0.0001), decreased lactose percent (4.75 +/- 0.03% vs. 4.99 +/- 0.03%, P 0.0001), increased milk log 10 SCC (4.22 +/- 0.05 vs. 4.41 +/- 0.05, P = 0.0004), and no differences in milk protein percent compared with CM half-udders. These results indicate that a 3x milking frequency in IM half-udders was not able to improve milk production compared with IM half-udders milked 2x. Our results indicate that 30% milk remaining in the gland had an irreversible impact on milk yield as increased milking frequency was not able to reverse the milk yield lost.