@conference {41226,
	title = {Seasonal variation of the fatty acid composition of milkfat from Friesian cows grazing pasture},
	booktitle = {Proceedings of the New Zealand Society of Animal Production},
	volume = {60},
	year = {2000},
	month = {Jan},
	pages = {314-317},
	publisher = {New Zealand Society of Animal Production},
	organization = {New Zealand Society of Animal Production},
	address = {Hamilton},
	abstract = {Information collected at the Dairying Research Corporation milk composition laboratories on the fatty acid composition
of milkfat spanning 1994/95 to 1998/99 dairying seasons has been summarised. The data comprised 1350 determinations
in 18 different experiments from 965 individual Friesian cows that calved in July/August and grazed solely on pasture. A
seasonal effect on fatty acid composition was observed. In general, concentrations of fatty acid groups and individual fatty
acids were similar in spring and autumn but differed in summer. The ratio of an estimate of preformed (total fatty acids
>C
17:0
) and an estimate of de novo- (total fatty acids <C
16:1
) synthesised fatty acids altered during the season. In early
lactation (August), the ratio of preformed:de novofatty acids (P:S) was 0.76 declining to 0.51 by December and increasing
to 0.80 by late autumn. The concentration of total unsaturated fatty acids followed a similar trend: 30.4\% in August,
24.5\% in December and 32.8\% in April. In early lactation, milkfat from primiparous compared with multiparous cows had
higher oleic acid (C
18:1
), total unsaturated fatty acids and P:S ratio, indicating greater mobilisation of body fat. Conjugated
linoleic acid (CLA) varied from 1-1.4\% through spring, declined to 1.0\% in summer and increased to 1.6\% by April. The
seasonal changes in milkfat composition reflected the seasonal trends in the characteristics of milkfat for processing. For
example the softness of milkfat as calculated from a relationship previously established between fatty acid composition
and solid fat content at 10
0
C (SFC10), varied seasonally. Milkfat was softer in late spring (SFC 10 , 53\%) becoming harder (SFC 10, 61-63\%) during December to February and softer (SFC 10, 54\%) in autumn. The healthiness of milkfat, as describedby the concentration of unsaturated fatty acids and CLA, varied throughout the season. The lowest concentrations were insummer or in mid-lactation and the highest in autumn or late lactation. The information will be useful to manufacturers ofdairy products to target specific milkfat products to particular times of the year.
},
	issn = {1176-5283},
	author = {Thomson NA and van der Poel W}
}
