MILK YIELD AND MAMMARY GROWTH EFFECTS DUE TO INCREASED MILKING FREQUENCY DURING EARLY LACTATION.

Authors: HALE, S - UNIV OF MARYLAND; Capuco, Anthony; ERDMAN, R - UNIV OF MARYLAND

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/6/2002
Publication Date: 6/1/2003
Citation: Hale, S.A., Capuco, A.V., Erdman, R.A. 2003. Milk yield and mammary growth effects due to increased milking frequency during early lactation.. Journal of Dairy Science. vol. 86(6), pp. 2061-71.

Interpretive Summary: One of the most common ways for dairy producers to increase milk production is by increasing milking frequency. Effects of increased milking frequency during early lactation were evaluated with regard to mammary growth and the long-term effects on milk yield. A novel approach utilizing four uneven milking intervals was employed to increase milking frequency with little additional labor and change in milking schedule. Cows that were milked twice daily (2X) for the first 21 days of lactation were compared with those that were milked four times daily (4X) for the first 21 days. The 4X cows were milked immediately before 2X cows and again approximately three hours later, at the end of the normal milking routine. All cows were milked 2X from d 21 through the remainder of lactation. Milking 4X during early lactation increased milk yield not only during the treatment period but elicited an 8% increase in milk yield for the entire lactation. The milk yield increase achieved with this protocol is approximately comparable to milk increases obtained with 3X milking throughout lactation. Data uggest that the increased milk production was associated with increased growth of the mammary secretory tissue. Increased milking frequency was equally effective when initiated immediately postpartum or after the milk withdrawal period (72 hours postpartum). Adoption of this protocol can increase milk production with minimal increase in labor costs or disruption of existing milking routine. However, further study is necessary to fully evaluate the impact on milk component yields.

Technical Abstract: Increased milking frequency (IMF) at the beginning of lactation has been shown to increase milk yield not only during IMF but also after its cessation. The objectives of this experiment evaluated the effects of increased milking frequency initiated during early lactation on mammary growth and effects on milk yield (MY). Thirty-one cows were divided into treatment groups: 1) 2X: cows milked twice daily (2X) beginning at parturition (day 1), 2) IMF1: cows milked four times daily (4X) from day 1 to 21 postpartum (PP) and 3) IMF4: cows milked 2X day 1 to 3 and 4X day 4 to 21 PP. The 4X cows were milked immediately before 2X cows and again ~3 h later, at the end of the normal milking routine. All cows were milked 2X from day 21 to 305 postpartum. Milk yields were 34.5, 37.8 and 37.6 kg/d during wk 1 to 44 for 2X, IMF1 and IMF4, respectively. Mammary biopsies from four cows per treatment were obtained on d 7 and 14 PP to evaluate mammary cell proliferation. Tritiated-thymidine incorporation tended to increase on day 7 in IMF1 cows, and arithmetic means of the percentage of cells expressing Ki-67 proliferation antigen were consistent with a proliferative response to IMF though not significant. Blood was sampled three times per wk during the first 2 wk and then once per wk during wk 3,4,5,6,8 and 10. Plasma insulin-like growth factor -1 (IGF-1) averaged 20.1 ng/ml in IMF cows vs. 24.2 in 2X but was not accompanied by a change in bST. Prolactin was also not affected by treatment. Neither milk yield nor potential effects on mammary cell proliferation were correlated with systemic IGF-1. However changes in local IGF-1 and its binding proteins cannot be discounted. Implementing an IMF routine increases MY during treatment and elicits a carryover effect on the remainder of lactation. Milk yield responses after an IMF routine may be the result of increased mammary cell proliferation.