Milk yield and mammary function in dairy cows milked four times daily

Abstract

Groups of lactating cows and heifers were milked four times daily in two diagonally opposed glands for 4 weeks, and the effects on milk yield studied relative to twice-daily milked glands as controls. Mammary enzyme activities, in vitro synthesis rates of milk constituents and histological scoring were determined in mammary biopsy samples obtained at the end of this period. These were used for assessment of mammary function. Frequent milking increased milk yield only in the treated glands, the contralateral control glands continuing to decline in yield at 2 %/week. There was no significant difference in response between cows and heifers; the mean increase in yield was 10-4%. The rate of decline in milk yield tended to decrease with frequent milking, to ~ 1 %/week. Consequently the yield of the treated glands continued to be elevated above that of the controls for some time after reversion to overall twice daily milking. Milk protein content was increased slightly by frequent milking. Mammary enzyme activities were ~ 18% higher in the treated glands than in the controls. Synthesis rates of lactose, casein and total protein were unaffected by milking frequency, but were all lower in the gland selected for the second biopsy, reflecting the reduction in milk yield caused by the first biopsy. DNA synthesis was increased by milking frequency, as were the size and number of epithelial cells in histological sections.

The number and activity of mammary epithelial cells, determining factors for milk production

“…During the first two weeks after changing over to milking thrice a day, this increase may be accompanied by an elevation in the enzyme activities of ACC, FAS and GT per cell unit, in the goat [40]. Comparable results have been obtained in the cow milked four times a day [41]. However, after 12 weeks, no difference was seen in the enzyme activities of udders milked twice and three times a day.…”

Short- and long-term effects of high milking frequency during the first 21 days of lactation on production and reproductive performance in high-lactating cows

“…Knight (2001) suggested that domestic animals selected for milk production are not dependent on PRL to support lactation, whereas growth hormone (GH) takes over some of the responsibility for maintaining milk yield. The hormone IGF-1 has been proposed as an important mediator of galactopoietic factors such as GH or bovine somatotropin (Wilde et al, 1987;Hillerton et al, 1990;Forsyth, 1996), who reported that increased IGF-1 concentration might in turn enhance both mammary differentiation and proliferation of mammary cells for goats and cows. We might assume that higher IGF-1 concentration 7 days after calving, as found in the present work, contributed to those two processes, followed by higher milk production during the entire lactation and the succeeding lactation as well.…”

Milk Removal: The Key to Maintaining Milk Production and a Tool to Enhance Efficiency

“…Hillerton et al (1990) observed an increase in activity of mammary enzymes, protein and lactose synthesis (in heifers only), DNA synthesis, and alveolar area in response to increased milking frequency, and concluded that cellular differentiation and proliferation were optimized with frequent milking. Hale et al (2003) reported an increase in mammary cell proliferation at 7 DIM in cows that were milked 4X for the first 3 wk of lactation compared to cows milked 2X; however, differences in proliferation were only observed in one of the two frequently milked cow groups.…”

“…Morag (1973b) reported that the increase in milk production in response to UFM occurs within 24 h, and the magnitude of the response was independent of previous milk production. In addition, heifers respond to UFM; Hillerton et al (1990) milked udder halves 2X or 4X for 4 wk during mid-lactation. In both cows and heifers, milk production of 4X udder halves increased by 10.4% relative to 2X udder halves (Hillerton et al, 1990).…”

“…In addition, heifers respond to UFM; Hillerton et al (1990) milked udder halves 2X or 4X for 4 wk during mid-lactation. In both cows and heifers, milk production of 4X udder halves increased by 10.4% relative to 2X udder halves (Hillerton et al, 1990). Tables 1 and 5.…”