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

University of Nebraska, Lincoln 68503

Abstract

Two experiments were conducted to study the relationship of rumen protozoa to lipid deposition 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. Treatments 1 and 2 were animals maintained with a "normal" microbial population, while treatments 3 and 4 were animals in which the protozoa numbers were maintained at or near zero.

Biopsy samples and tissue samples obtained from five different areas of the carcass revealed a change in the fatty acid composition of the adipose tissues. As the animals matured, greater quantities of unsaturated fatty acids were deposited. Also noted was a significant difference in the degree of unsaturation of subcutaneous fat as compared to abdominal fat. The presence or absence of rumen protozoa significantly altered the tissue levels of margaric, stearic and linoleic acids. The lower molar percent of linoleic acid found in the depot fat as compared to the level found in the serum suggests that unsaturated fatty acids are not deposited efficiently at the depot sites or they are rapidly metabolized and hydrogenated after being deposited. The 8- to 12-fold difference in serum and tissue levels of linoleic acid clearly indicates that some factor along with microbial hydrogenation is responsible for the high degree of saturation attained in ruminant fats.

¹ Published with the approval of the Director as Paper No. 3479. 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.