EFFECT OF DIETARY FISH OIL ON THE FATTY ACID COMPOSITION 

 AND PALATABILITY OF PIG TISSUES' 



Robert R. Kifer,° Preston Smith, Jr..'' and Edgar P. Young" 



ABSTRACT 



Basically, this report deals with the problem of a "fishy" flavor in the meat of pigs, which sometimes 

 results when pigs are fed fishery products, such as fish meal, above a certain concentration in the diet. 



In this study, pigs were fed diets containing fish oil to investigate specifically: (1) the effect, on 

 the taste of the meat, of feeding pigs fish oil, (2) the effect, on the taste of the meat, of withdrawing 

 the oil from the diet at given times, (3) the fatty acid composition of the various body tissues of the pigs, 

 and (4) the relation of composition to the taste of the meat. 



The principal findings of the study were: (1) The amount of the fish oil co3 fatty acids fed and de- 

 posited was significantly positively correlated with the weighted organoleptic score' when the pigs were 

 fed the oil containing diets to a market weight of 90.9 kg. (2) Removal of the fish oil from the pigs' 

 diets when the pigs obtained body weight (of either 68.0 or 79.5 kg) resulted in a loss of the signifi- 

 cant positive correlation above. (.3) Differences in the degree of unsaturation and in fatty acid comp- 

 osition were found among the oils in the tissues examined. (4) A signifiant positive correlation was 

 obtained between the quantity of the characteristic fatty acids (&>3) of fish oil fed and the quantity de- 

 posited in three of the four tissues examined, the exception being the longissimtis dorsi tissue. 



Both the processors of fishery industrial prod- 

 ucts and the feed manufacturers who use the 

 products are sometimes confronted with the 

 problem of a fishy flavor in the carcasses of 

 animals fed diets in which these products are 

 included. Fish oil fed directly to the animals 

 or fed as a residual component of fish meal or 

 of fish solubles has been shown to pi-oduce an 

 off-flavor under certain conditions (Banks and 

 Hilditch, 1932; Hilditch and Williams, 1964). 

 Through practical research, the problem has 

 been partly solved by reducing the quantity (that 

 is, the percentage) of fish oil in the diet or by 

 eliminating the oil during an interval of time 

 before the animals are marketed (Frazer, Stot- 

 hart, and Gutteridge, 1934). This latter tech- 

 nique is not always effective, especially when 

 fairly high (8.25'^r) levels of fish oil have been 

 fed (Anglemier and Oldfield, 1957). 



' Contribution number 4304 Maryland Agriculture 

 Experiment Station, Department of Animal Science, 

 Project number C33-Scientific Article A-1586. 



' National Marine Fisheries Service, Washington, 

 D.C. 20235. 



" Department of Animal Science, University of Mary- 

 land, College Park, Md. 20740. 



' Note the organoleptic score increased with greater 

 unacceptability. 



Manuscript received January 1971. 



FISHERY BULLETIN: VOL. 69. NO. 2, 1971. 



Investigations to relate more specifically the 

 causal agents of the oflF flavor resulting from 

 the use of fish oil have led to the hypothesis 

 that the long-chain polyunsaturated fatty acids 

 of the C20-22 series commonly found in fish oil 

 are pi-ecursors of the flavor-producing compo- 

 nents (Banks and Hilditch, 1932; Marion and 

 Woodroof , 1963 ; Miller, Gruger, Leong, and 

 Knobl, 1967). Investigations by the Animal 

 Nutrition Unit of the Bureau of Commercial 

 Fisheries (now the National Marine Fisheries 

 Service) Technological Laboratory, College 

 Park, Md., using chickens, have indicated that 

 a further partitioning of the C2(i 22 fatty acid 

 series results in a positive correlation between 

 individual fatty acids of these series deposited 

 and the detection of the off-flavor (Miller et al., 

 1967). 



In a continuation of this line of investigation, 

 the work reported here was divided into four 

 experiments. Their purposes were to determine 

 the following information: 



1. The relation between the menhaden-oil fat- 

 ty acid fed and the fatty acid pattern of tissue 

 samples (namely, those of the outer and the in- 



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