Graduate Thesis Or Dissertation
 

The fatty acid composition of certain bovine tissues

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  • In this study subcutaneous, inter- and intramuscular fats from 42 Hereford steers were analyzed for their fatty acid composition using gas-liquid chromatography. The same tissues were analyzed from one pair each of identical twins of Angus and Shorthorn breeding. Muscle and liver lipids from these latter four animals were fractionated on silicic acid columns into glycerides and phospholipids prior to the fatty acid analysis. Feedlot performance and carcass characteristics data were also available on these animals. The data were analyzed statistically using analysis of variance techniques and simple correlations were calculated between all the variables studied with the exception of linolenic acid. Of the ten fatty acids quantitated, only the 17-carbon fatty acid and an 18-carbon branched chain acid were found to differ significantly between rations. Since both these acids are believed to be synthesized by certain rumen bacteria, these differences may reflect conditions in the rumen. No direct evidence is available. However, it is probable that this involves the availability of suitable precursors or rumen conditions favorable to these species of organisms. A highly significant relationship (r = .47) was found between average daily gain and linoleic acid. This relationship is probably also influenced by conditions in the rumen. A more rapid rate of passage or other factors which result in less extensive hydrogenation of polyunsaturated acids might also be conducive to more rapid growth. Essential fatty acids, such as linoleic, might be expected to reduce growth rates when they are deficient, however, no evidence of such a deficiency existed. Backfat thickness gave highly significant negative correlations with both myristic (r = .44) and palmitic acid (4 = .46) and was positively related to the 17- and 18-carbon fatty acids with the exception of stearic. Rib-eye area/CWT and estimated cutability, conversely, were positively and highly significantly correlated with the 14- and 16-carbon fatty acids and showed a negative relationship with the longer chained fatty acids. These relationships may indicate metabolic differences between the animals which deposit more lean tissue with less fat and those depositing greater amounts of fat. If, as these data indicate, meatier animals accumulate more of the 14- and 16-carbon fatty acids in the subcutaneous fat, a useful selection tool will be provided to the animal breeder. These 14- and 16-carbon fatty acids, in general showed a positive relationship between one another. When correlated with the 17- and 18-carbon fatty acids a negative relationship was observed. These negative relationships were particularly pronounced in the case of oleic and linoleic acids. It was suggested that the substitution of shorter chain saturated fatty acids for the longer chain unsaturates is the result of an attempt by the animal to maintain physical homeostasis of its depot fats. This assumption is based on the observation that the removal of carbon atoms has the same effect on some of the physical properties as the addition of a double bond. The data obtained in this study indicated that myristic and palmitic acid were readily substituted for oleic acid. The separation of liver and muscle lipid into glyceride and phospholipid resulted in the detection of additional components. Both muscle and liver phospholipids contained large amounts of arachidonic and eicosatrienoic acids. These acids were detected only in liver glycerides. An unknown fraction was observed in both liver glycerides and phospholipids and in muscle phospholipid. This fraction may represent a fatty aldehyde since they have been previously reported in the liver as free aldehydes and as constituents of phospholipid. The only fraction showing similar trends within twin pairs was the muscle glycerides. The muscle phospholipids and all the liver fractions showed considerable variability both within and between twin pairs.
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