Seasonal variations in fatty acid composition of New Zealand butterfat

Abstract

Six butterfats taken at approx. 2-month intervals throughout the season were subjected to ester-fractionation analyses in triplicate and the standard deviation for each constituent calculated. Throughout the season, beginning in July, the content of C6-C14 saturated acids (and total saturated acids) increased regularly up to Nov., and thereafter declined slowly to the end of the season. The C18 unsaturated acids varied in the reverse direction to that of the C6-C14 constituents. The butyric acid content changed irregularly, but tended to decline throughout the season. Palmitic acid showed little change, but when expressed as a percentage of the total satd. acids, it tended to increase throughout the season. In comparing butterfats samples at 2 -month intervals during 1 year, significant differences existed between many of the fatty acid constituents. Extreme differences in composition were exhibited by the May and Nov. samples; of the 13 differences, 10 were assessed to be significant at the 1% level. Comparing the butterfats taken during the same month, but in different years, significant differences were observed between certain of the component fatty acids. However, the differences were small, and this fat, together with Cox and McDowall''s (Jour. Dairy Res. 15: 377. 1948) results showing the similarity between the constants of butterfats sampled during the same months of different yrs., is sufficient to indicate that the present study would serve as a guide for predicting the fatty acid composition of New Zealand butterfat for any given month. The variations in content of Cl8 unsaturated acids reflect the influence of the changing plane of nutrition throughout the year and at the same time are consistent with the changes observed by Bartley et al. (Jour. Dairy Sci. 34: 536. 1951) to accompany the progression of lactation.