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The Effect of Feeding Unsaturated Fats as Influenced by Gelatinized Corn and by the Presence or Absence of Rumen Protozoa. I. Serum Lipid Composition¹

University of Nebraska, Lincoln 68503

Abstract

Two experiments were conducted to study the relationship of rumen protozoa to lipid metabolism in cattle. Four treatments were used in these experiments: 1) cracked corn, 2) cracked corn plus 5% unsaturated fat, 3) gelatinized corn and 4) gelatinized corn plus 5% unsaturated fat. The gelatinized corn was used to remove rumen protozoa from half the experimental animals. In experiments 1 and 2, respectively, 5% safflower oil and 5% soybean oil were used as the source of unsaturated fatty acids. In this manner it was possible to study the effects of a "normal" microbial population (cracked corn fed animals) and compare these effects to those obtained when protozoa were absent from the rumen. Further studies were made relating dietary treatments, rumen fermentation and serum lipid composition.

In the initial experiment using identical twin Angus steers, rumen and blood samples were obtained four times in the first seven days and bi-weekly thereafter for the 130-day feeding period. A rapid reduction in the rumen protozoa concentration in the animals fed gelatinized corn was noted during the first week on experiment. The protozoa numbers were maintained at or near zero for the remainder of the experiment. Associated with the reduction in rumen protozoa concentration were a drop in rumen pH and an increase in total VPA concentration, compared to cracked corn fed animals.

As both experiments progressed, total serum lipids were observed to increase as well as the molar percent linoleic acid. Stearic and oleic acid concentrations decreased while palmitic acid levels remained somewhat stable. In the absence of rumen protozoa, linoleic acid levels were higher and oleic and stearic acid levels were lower, when compared to animals maintaining a "normal" protozoa population. The addition of 5% unsaturated fat to the rations appeared to increase total blood lipids slightly. Significantly higher serum linoleic acid levels were obtained when oil was added to the rations. The other fatty acids measured were relatively unaffected by the level of dietary fat.

¹ Published with the approval of the Director as Paper No. 3478. Journal Series, Nebraska Agricultural Experiment Station. Research reported was conducted under project no. 13–14.

² Present address: College of Vet. Medicine, Cornell University, Ithaca, New York 14850.

³ Present address: Departmental Chairman, Department of Animal Science, Purdue University, Lafayette, Indiana 47907.