Influence of milking three times a day on milk quality.

Lactations were divided into three periods: early (1 to 99 d), mid (100 to 199 d), and late (200 to 299 d). One hundred Holsteins were randomly split into four groups that were balanced for parity. Groups 222 and 333 were milked twice and three times a day, respectively, throughout lactation. Group 233 was switched from twice to three times daily milking at 100 d, and group 223 was switched at 200 d. Compared with group 222, milk yield for group 333 increased by 10.4%, and fat and protein yields increased by 4.7 and 7.3%, respectively. Mean milk SCC for all groups was < 175,000 cells/ml within each lactation period. The percentage of CP was lower for cows milked three times a day than for cows milked twice a day during each stage of lactation (early, 2.78 and 2.91; mid, 3.08 and 3.19; and late, 3.16 and 3.28, respectively). Casein as a percentage of CP was significantly higher for cows milked three times a day during midlactation. The acid degree values (milliequivalents of FFA/ 100 g of fat) were significantly higher for milk from cows milked three times a day than for cows milked twice a day during early and midlactation, (early, 0.75 and 0.55; mid, 0.82 and 0.61; and late, 0.88 and 0.75, respectively). No differences were detected in milk flavor or plasmin activity because of milking frequency. Casein as a percentage of CP decreased, and plasmin activity increased, as parity and stage of lactation increased.