Influence of dietary fish oil on conjugated linoleic acid and other fatty acids in milk fat from lactating dairy cows

Lactating cows were fed menhaden fish oil to elevate concentrations of conj ugated linoleic acid, transvaccenic acid, and n-3 fatty acids in milk. Twel ve multiparous Holstein cows at 48 +/- 11 DIM were assigned randomly to a r eplicated 4 x 4 Latin square. Each treatment period was 35 d in length, wit h data collected d 15 to 35 of each period. On a dry matter (DM) basis, die ts contained 25% corn silage, 25% alfalfa hay, and 50% of the respective co ncentrate mix. Fish oil was supplemented at 0, 1, 2, and 3% of ration DM. L inear decreases were observed for DM intake (28.8, 28.5, 23.4, and 20.4 kg/ d) and milk fat (2.99, 2.79, 2.37, and 2.30%) for 0 to 3% dietary fish oil, respectively. Milk yield (31.7, 34.2, 32.3, and 27.4 kg/d) increased as di etary fish oil increased from 0 to 1% but decreased linearly from 1 to 3% d ietary fish oil. Milk protein percentages (3.17, 3.19, 3.21, and 3.17) were similar for all treatments. When the 2% fish oil diet was fed, concentrati ons of conjugated linoleic acid and transvaccenic acid in milk fat increase d to 356% (to 2.2 g/ 100 g of total fatty acids) and 502% (to 6.1 g/100 g), respectively, of amounts when 0% fish oil was fed. There were no additiona l increases in these fatty acids when cows were fed 3% fish oil. The n-3 fa tty acids increased from a trace to over 1 g/100 g of milk fatty acids, whe n the 3% fish oil diet was fed. Fish oil supplementation to diets of dairy cows increased the conjugated linoleic acid, transvaccenic acid, and n-3 fa tty acids in milk.