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

Abstract

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.