Restricted feeding and linseed oil as modifiers of the fatty acid profile in pork

Thirty-two fatteners were divided into 4 groups: two of them were fed semi ad libitum (A) during the growing (22-60 kg) and finishing (60-102 kg) periods of fattening and two, a restricted (-25%) amount of feed (R) in the growing period and semi ad libitum in the finishing period. During the finishing period within each level of feeding, one group received 0 (AC and RC) and the other 4% (AO and RO) linseed oil. Pigs fed the restricted amount of feed had a more beneficial fatty acid profile in the M. longissimus dorsi and M. semimembranosus, however, the differences were not statistically significant. The 4% supplement of linseed oil in the finishing diets caused an increase in the PUFA content, of n-3 in particular.


INTRODUCTION
The main criteria for evaluating the functional properties of pork are its total fat and cholesterol contents and fatty acid profile.The SFA, MUFA and PUFA ratios are the most important (Wood et al., 2003).It is known that the fat content in pork increases most in the finishing period of fattening and that the composition of the feedstuff can influence the fatty acid profile of pork.The aim of the study was to evaluate the influence of restricted feeding during the growing period of fattening and linseed oil supplementation in finishing diets on the fatty acid profile of pork.

MATERIAŁ AND METHODS
Thirty-two fatteners were divided into 4 groups: two of them were fed semi ad libitum (A) during the growing (22-60 kg) and finishing (60-102 kg) periods of fattening and two, restricted (-25%) amounts of feed (R) in the growing period and semi ad libitum in the finishing period.Within each level of feeding, during the finishing period one group received 0 (AC and RC) and the other 4% (AO and RO) linseed oil.The composition and nutritive value of the experimental diets are shown in Table 1.After slaughter, samples of the M. longissimus dorsi (13-14 rib) and of the M. semimembranosus from the right half-carcasses of all of the animals were taken to determine the fatty acid profile (ISO 5509, 1978 andISO 5508, 1990).The results were subjected to one-way analysis of variance employing Duncan's multiple rangę test (SPSS, 2000).

RESULTS
The lipid fraction of the M. longissimus dorsi from fatteners from groups AO and RO contained, in comparison with AC and RC, a larger amount of SFA (differences were not significant) and PUFA n-3 (P<0.001),but in the lipid fraction of the M. semimembranosus, these differences concerned both PUFA n-6 and PUFA n-3 were significant (P<0.001).Supplementation of the diets with linseed oil narrowed the PUFA n-6:PUFA n-3 ratio.A more beneficial fatty acid profile, PUFA n-6:PUFA n-3, and PUFA:SFA ratios were found in fatteners fed restricted amounts of feed in the growing period of fattening in comparison with fatteners fed semi ad libitum during the whole fattening period.

DISCUSSION
Numerous experiments have demonstrated that there is a close correlation between the ąuantity of fatty acids in feed and in the lipid fraction of pork (Nguyen et al., 2003).Increasing PUFA n-3 in a diet by adding fish oil or vegetable oil, particularly linseed oil, can beneficially affect the lipid composition of pork (Muriel et al., 2002;Raes et al., 2004); the PUFA n-6/n-3 ratio can even be decreased to under the value of 3 (Enser et al., 2000).Compensatory growth can change fat deposition in the finishing period, and when oil containing more PUFA is fed during this period, the fatty acid profile can be improved.

CONCLUSIONS
Linseed oil-supplemented diets beneficially infiuenced the fatty acid profile in pork fat.Restricted feeding itself does not markedly influence the fatty acid profile, but when linseed oil is fed in the finishing period of fattening, an increase in PUFA incorporated into the fat from the diet was observed.

TABLE 2
Fatty acid profile, % of sum of fatty acids