Effect of Diet on Fatty Acid Composition of Body Fat in Steers

Summary

Two experiments were conducted with beef steers to study the effect of physical form of diet and ratio of dried citrus meal to corn meal in the diet on degree of unsaturation of rib and kidney fat. Rumen volatile fatty acids were measured and related to degree of unsaturation of body fat.

No differences were found in degree of unsaturation of kidney fat among groups of steers fed high concentrate diets containing either flaked or ground corn and a pelleted diet containing corn meal. Fatty acid composition and iodine number of fat over the 13th rib revealed that diets containing 72% corn produced a higher (P<.05) degree of unsaturation than diets containing either 31.6% dried citrus meal: 36.0% corn or 63.2% dried citrus meal. The higher unsaturation of fat in corn-fed steers was due to a higher (P<.01) oleic acid and a lower (P<.01) palmitic acid content. These changes were ascorn diets. Rib fat was more unsaturated than sociated with a higher starch content in the kidney fat because of a lower stearic and a higher palmitoleic and oleic acid content.

Rumen microbial metabolism, evidenced by proportions of volatile fatty acids in rumen fluid, was altered by changes in ratios of dried citrus meal to corn meal in diets. High correlation coefficients of −1.0 and 1.0 were found between dietary starch and molar proportions of ruminal acetate and propionate, respectively. The acetate to propionate ratio was narrowest (P<.01) when the starch content of the diet was highest. Correlation coefficients of 0.58, −.57 and 0.51 were found between acetate to propionate ratio in rumen fluid and palmitic acid, oleic acid and iodine number of rib fat, respectively.

© American Society of Animal Science 1965