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* Department of Animal Science
Department of Human Nutritional Sciences University of Manitoba, Winnipeg, Manitoba, Canada, R3T 2N2
Corresponding author: Karin Wittenberg; e-mail:
km_wittenberg{at}umanitoba.ca.
Two experiments were run concurrently to determine the effect of fresh forage consumption on the production and proportions of plasma and milk fat vaccenic acid (VA), conjugated linoleic acid (CLA), and linolenic acid in dairy cattle. In experiment 1, the cows consumed 50, 65, and 80% of their feed intake as pasture with the remainder of intake as a barley-based concentrate. The proportion of VA in milk fatty acids increased 12% when pasture intake increased from 50 to 65% of total dry matter intake and VA, CLA, and linolenic acid proportions increased 26, 18, and 27%, respectively, as pasture increased from 65 to 80% of dietary intake. In experiment 2, fresh forage was compared to conserved hay (cut from the same pasture the previous summer) to determine the effect on plasma and milk fat VA, CLA, and linolenic acid. Also, the effect of crushed solin seed (a flax cultivar that is high in linoleic acid) supplementation to the fresh forage diet was determined. Fresh forage compared to conserved hay in the diet, increased the proportion of CLA in the plasma very low density lipoproteins (VLDL) fraction by 71% but had no effect on linolenic acid. Supplementation of the fresh forage diet with a linoleic acid source increased VA and CLA in the plasma VLDL fraction 25 and 58% and slightly decreased the proportion of linolenic acid. Fresh forage, compared to conserved hay, increased milk fat VA and CLA proportions by 22 and 15%. Supplementing the fresh forage diet with linoleic acid from crushed solin seed further increased milk fat VA and CLA proportions 41 and 25%. Solin supplementation in a lactation diet is a superior method to increase CLA levels in milk fat than feeding fresh forage alone.
Key Words: linoleic acid solin milk fat very low density lipoproteins CLA
Abbreviation key: CLA = conjugated linoleic acid, FAME = fatty acid methyl esters, FF = fresh forage, FFT = fresh forage plus tallow diet, FFS = fresh forage plus solin diet, HT = hay diet, LHDL = low and high density lipoproteins, VA = vaccenic acid, VLDL = very low density lipoproteins
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