Effect of adding fat to the diet for lambs on the fatty acid pro fi le of intramuscular , perirenal and subcutaneous fat

The aim of the experiment was to determine the effect of rapeseed, soyabean, linseed, and fi sh oil as sources of polyunsaturated fatty acids in lamb diets on the fatty acid composition of intramuscular, subcutaneous and perirenal fat. Thirty fattened lambs of an average body weight of 22±3 kg were divided into fi ve groups and fed a control diet without added oil, or experimental diets supplemented with 4% of a given oil. Linseed oil reduced (P≤0.01) the ratio of n-6 to n-3 polyunsaturated fatty acids to the desired value, whereas both soyabean or fi sh oil raised (P≤0.01) this ratio in intramuscular fat. Linseed oil increased (P≤0.05), but rapeseed and fi sh oil decreased the level of monounsaturated fatty acids in perirenal fat. None of the oils affected the fatty acid concentration in subcutaneous fat. All supplemented oils increased (P≤0.05) intramuscular CLA. The highest was from 28.8 μg/g fat in control group to 33.3, 48.2, 53.4 and 97.1, respectively, with rapeseed oil, soyabean oil, linseed oil and fi sh oil addition. An increased CLA concentration in perirenal and subcutaneous fat was observed when linseed oil was added to the diets.


INTRODUCTION
The fatty acid profi le of body lipids can be modifi ed with most lipid sources in the diet, but not to a large extent (Doreau and Chilliard, 1997).According to Mir et al. (2002) supplementing diets for cattle with oils could be applied to alter the fatty acid profi le of adipose but not of intramuscular fat.Dietary vegetable oil supplementation could be used to substantially increase the conjugated linoleic acid (CLA) content of muscle fat.Beaulieu et al. (2002) suggested that supplementinghigh-concentrate fi nishing diets with soyabean oil or other sources of linoleic acid is not an effi cacious method for increasing the CLA cis 9,trans11 isomer in tissues.The conjugated linoleic acid content of tissues is higher in ruminants compared with non-ruminants, and among ruminants, lamb tissues are characterized as having the highest level of CLA.Mir et al. (2002) demonstrated that the CLA content in lamb muscle is altered by oil supplemented to the diet.
Given the increasing demand for meat and meat products rich in polyunsaturated fatty acids, including CLA, the objective of the experiment was to determine the effect of different oils as sources of polyunsaturated fatty acids on the fatty acid composition in lamb meat.

MATERIAL AND METHODS
Thirty fattened lambs of 22±3 kg body weight were divided into fi ve groups and fed ad libitum meadow hay and concentrate without added oil as controls, or with the addition of 4% rapeseed oil (RSO) as a source of C18:1, soyabean oil (SBO) as a source of C18:2, linseed oil (LSO) as a source of C18:3, or fi sh oil (FO) as a source of long-chain polyunsaturated fatty acids.The concentrate consisted of, %: wheat meal, 60; rapeseed oilmeal, 18; mineral mixture, 2; and wheat bran, 20 in the control diet.The composition of experimental diets was as follows: wheat meal, 60; rapeseed oilmeal, 18; mineral mixture, 2; and wheat bran, 16; oil supplement, 4.
Total fatty acid content and composition of intramuscular (IT), perirenal (PR) and subcutaneous (SC) fats were determined according to procedures of Czauderna et al. (2001).All data were analysed using SAS procedures (User's Guide, 1990).

RESULTS
Only few effects of the added oils on the fatty acid composition of lamb fat were observed.Linseed oil reduced (P≤0.01) the ratio of n-6 to n-3 polyunsaturated fatty acids to the desired level (2,3:1), whereas both soyabean and fi sh oils increased (P≤0.01) the ratio in intramuscular fat, respectively, to 7,0:1 and 9,3:1 (Table 1).
Linseed oil also increased (P≤0.05) the level of monounsaturated fatty acids in perirenal fat.Rapeseed and fi sh oils had a slight, but signifi cant, effect on the MUFA level (Table 2).None of the oils effected the fatty acid composition of subcutaneous fat (Table 3).The CLA content in intramusular fat was affected (P≤0.05) in all experimental groups.Addition of 4% linseed oil into the diet increased (P≤0.05) the level of CLA in subcutaneous fat and perirenal fat when compared with the control group.

DISCUSSION
Ruminant meat, particularly lamb meat, is a rich source of n-6 and n-3 PUFA, conjugated linoleic acid plays a favourable role in the prevention and reduction of major diseases of civilization in humans (Geay et al., 2001).Therefore, it is recommended to increase the level of the desired fatty acids in meat fat.Our results showed a slight but not signifi cant decrease of the saturated fatty acid level when diets were supplemented with 4% of oils.Ponnampalam et al. (2000) suggested that particularly fi sh oil can have a positive effect on polyunsaturated fatty acids (mostly n-3) in meat.However, we did not observe the expected increase in polyunsaturated fatty acid content, especially when fi sh oil was supplemented to lamb diets, but fi sh oil signifi cantly increased the CLA level in intramuscular fat.Other oils, sources of C18 unsaturated fatty acids, did not affect the fatty acid profi le but increased the CLA level.The results obtained in this study are similar to those of Mir et al. (2002), in which sunfl ower oil did not affect muscle fat content but increased (P≤0.01) the conjugated fatty acid concentration by about four-fold.

CONCLUSIONS
Inclusion of vegetable or fi sh oil to the diet for sheep increased the level of CLA in the fat of lambs but did not increase the polyunsaturated fatty acid level or decrease the saturated fatty acid level.There was a tendency toward a decreased n-6: n-3 ratio when linseed oil was added to the diet.

Table 1 .
Fatty acid concentrations in intramuscular fat, mg/g fat

Table 3 .
Fatty acid concentrations in subcutaneous fat, mg/g fat