Letter | Published:

Growth of Ryegrass-dominant Pasture grazed by Cows, and Properties of New Zealand Butterfat

Naturevolume 191pages303304 (1961) | Download Citation



MARKED and regularly recurring seasonal fluctuations in the characteristics of New Zealand butterfat have been reported by Cox and McDowall1. The iodine value, for example, rises to a maximum of about 41 in mid-winter, falls gradually until the beginning of October and then rapidly during October and November to a mid-summer minimum of about 34, and rises again during the autumn and early winter to the mid-winter maximum. The carotene and vitamin A contents of the butterfat also have been shown by McDowell and McDowall2 to change according to a regular seasonal pattern, with maximum values in the early spring and minimum values in mid-summer. These latter changes have been found by McGillivray3 to be a reflexion of changes in the carotene and vitamin A contents of the blood plasma.

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  1. 1

    Cox, G. A., and McDowall, F. H., J. Dairy Res., 15, 377 (1948).

  2. 2

    McDowell, A. K. R., and McDowall, F. H., J. Dairy Res., 20, 76 (1953).

  3. 3

    McGillivray, W. A., J. Dairy Res., 24, 95 (1957).

  4. 4

    Worker, N. G., and McGillivray, W. A., J. Dairy. Res., 24, 85 (1957).

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  1. Dairy Research Institute, and Massey Agricultural College, Palmerston North, New Zealand

    • F. H. McDOWALL
    • , W. A. McGALLIVRAY
    •  & J. C. HAWKE


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