Origin of Plasma Fatty Acids in Lactating Cows Fed High Grain or High Fat Diets

Abstract

Palmitate-l-14C was given to lactating cows in 20 trials involving four dietary treatments and two different routes of tracer administration. The specific activitytime curve of 14-C' activity in milk fat was resolved by curve analysis into two components, a rapid-turnover component attributed to exogenous (dietary) fatty acid and a slower turnover component attributed to adipose tissue. Administration of palmitate-lJ4C abomasally or orally gave greater (P < 0.01) estimates of exogenous fatty acid than did intravenous dosing. A high grain-restricted roughage diet reduced (P < 0.01) the exogenous estimate, presunmbly due to increased uptake of dietary fatty acid by adipose tissue. A low-fat diet also lowered the estimate of exogenous fatty acid. A high-fat diet reduced the turnover time of the adipose tissue pool by 30% whereas the high grain restricted roughage diet increased the turnover time by 26%. Estimates of the effects of dietary treatments on rate constants of fatty acid transfer in a 2-pool model are presented.