Abstract
The production of intermediates during hydrogenation of conjugated linoleic acid (CLA) isomers was determined by infusing a CLA mixture (41% cis9,trans11-18:2 and 44% trans10,cis12-18:2) into the rumen of lactating cows. Four Holstein cows fed a basal diet were infused for 48 h with doses of 0, 45, 90, or 180 g CLA .d -1 into the rumen. Treatments were ran- domly assigned in a 4 〈 4 Latin square with 4-d experimental periods, and a 7-d transition between periods. Milk samples were obtained at -12 and 0 h before infusion, and at 12 h intervals from 0 to 96 h after infusion. Milk yield and DMI were not affected by treatment. Milk fat concentration was 12% lower, causing an 18% decrease in fat yield, when 180 g CLA.d -1 was infused. Concentration of trans11-18:1 in blood plasma increased in proportion to CLA dose. Trans10-18:1 concentration in blood plasma also increased, and was 240% greater when CLA was infused at 180 g.d -1 . Trans10,cis12-18:2 was strictly a function of exogenous CLA input into the rumen, and ranged from 0.2 to 0.7 mg.g -1 of total plasma fatty acids. Yields of saturated 6:0 to 16:0 in milk fat decreased by 87 g.d -1 when 180 g CLA.d -1 was infused. Stearic acid concentration and yield increased by 25 and 6%, but cis9-18:1 yield decreased, in response to increasing dose of CLA. Yields of trans11-18:1 and cis9,trans11-18:2 increased in proportion to CLA dose infused. Transfer rates of infused cis9,trans 11-18:2 or trans10,cis12-18:2 into milk fat averaged 3% at the highest dose of CLA infused. Milk fat yields of trans10-18:1 and trans10,cis12-18:2 also increased in proportion to CLA input. Lower normalized ratios of cis9-18:1 to 18:0 and cis9,trans11-18:2 to trans11-18:1 in milk fat when CLA was infused suggested CLA reduced desaturation in the mammary gland. Results provide additional evidence that enhanced flow of trans10-18:1 or trans10,cis12-18:2 from the rumen may decrease milk fat yield by reducing de novo synthesis and desaturation.
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