Effects of Pasture Allowance on the Yield and Composition of Milk from Cows of Different ß-Lactoglobulin Phenotypes

¹ Dairying Research Corporation Ltd., Private Bag 3123, Hamilton, New Zealand
² New Zealand Dairy Research Institute, Private Bag 11 029, Palmerston North, New Zealand
³ AgResearch, Ruakura Research Centre, Private Bag 3123, Hamilton, New Zealand

The objective of this study was to determine whether the differences in the composition of milk from cows of different ß-lactoglobulin (ß-LG) phenotypes are affected by the amount of pasture available and, hence, pasture dry matter intake. Twenty-two Friesian cows of each of the AA and BB variants of the ß-LG phenotype were subjected to ad libitum grazing or restricted grazing in crossover experiments during spring (early lactation, 60 d in milk) and summer (mid to late lactation, 180 d in milk). Milk samples were collected from each cow at the end of each 8-d treatment period and analyzed for composition. Cows of the AA variant of the ß-LG phenotype had higher concentrations of whey protein and ß-LG, but lower concentrations of casein (CN), -CN, -CN (summer only), and BSA, than cows of the BB variant. Compared with cows with a restricted allowance, cows grazing ad libitum had higher milk yields and concentrations of protein, casein, whey protein, and all individual proteins except BSA and immunoglobulin. There were no interactions between effects of pasture allowance and phenotype on milk yield or composition. The data show that having adequate pasture for grazing cows is important not only to maximize milk yield, but also to optimize concentrations of protein and casein, and hence the manufacturing potential of milk. Further, the differences in composition of milk from cows of differing ß-LG phenotypes persisted during short-term restrictions in pasture allowance, and between spring and summer.

Key Words: pasture allowance • milk composition • ßbeta;-lactoglobulin phenotype

Submitted on December 8, 1999
Accepted on March 20, 2000

This article has been cited by other articles:

				J. K. Kay, T. R. Mackle, D. E. Bauman, N. A. Thomson, and L. H. Baumgard Effects of a Supplement Containing Trans-10, Cis-12 Conjugated Linoleic Acid on Bioenergetic and Milk Production Parameters in Grazing Dairy Cows Offered Ad Libitum or Restricted Pasture J Dairy Sci, February 1, 2007; 90(2): 721 - 730. [Abstract] [Full Text] [PDF]

				F. Buckley, K. O'Sullivan, J. F. Mee, R. D. Evans, and P. Dillon Relationships Among Milk Yield, Body Condition, Cow Weight, and Reproduction in Spring-Calved Holstein-Friesians J Dairy Sci, July 1, 2003; 86(7): 2308 - 2319. [Abstract] [Full Text] [PDF]