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

Department of Dairy Science, Ohio Agricultural Research and Development Center, Wooster 44691

ABSTRACT

Palmitate-1-¹⁴C 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-1-¹⁴C 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, presumably 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 tirne by 26%. Estimates of the effects of dietary treatments on rate constants of fatty acid iransfer in a 2-pool model are presented.

Low fat and high grain restricted roughage diets reduced plasma free fatty acids ( P < 0.01 and 0.001). The high grain restricted rouglhage diet increased plasma glucose and serum heparin-precipitable lipoprotein esters (P < 0.01 and 0.001).