The effects of different amounts and types of fat on milk fatty acid composition in sheep *

Four milking ewes (50±5 kg) were used in a 4 x 4 Latin square experiments to determine the effects of different sources and amounts of vegetable-origin fat in the diet on the fatty acid composition of milk. Ewes of the control group were fed a diet consisting of meadow hay and concentrate (60:40) that was supplemented for the experimental groups with rape seed oil, hydrogenated rape seed oil, or linseed oil at a level 4, 8 or 10% in dry matter of the diet. Addition of linseed and rape seed oil to the diet decreased (PO.05, PO.01) the level of total saturated fatty acids in milk. Rape seed oil and hydrogenated rape seed oil caused significant (PO.05, PO.01) increases in the level of mono-unsaturated fatty acids, whereas significant differences were not reached (P>0.05) when linseed oil was fed to sheep. Also, the total amount of PUFA+MUFA increased in milk (PO.05, PO.01) when diets with linseed and rape seed oil were fed. The level of stearic acid differed depending on the added fat. A lower (PO.01) level of stearic acid was observed when 8% of linseed oil was added, whereas it was higher (PO.05) when 10% of linseed oil and 8% and 10% of rape seed oil were added to the ration. Feeding ruminants rations supplemented with fat of vegetable origin increased the energy content of the diet and also improved the level of desirable fatty acids in milk, e.g., MUFA and PUFA, which may be recommended in the treatment of some diseases.


INTRODUCTION
In response to nutritional guidelines recommending reduction in saturated fats in human diets, farmers have to develop new products containing unsatura ted fats to satisfy the demand of the more health-conscious consumer (During et al., 2000).The body fat of farm animals is partly synthesized from dietary carbo hydrates, partly from dietary fatty acids.In ruminants, polyunsaturated fatty acids are hydrogenated mainly to saturated fatty acids by rumen microorganisms and then absorbed and deposited in adipose and muscle tissue.It is relatively easy to change the fatty acid composition of lamb and veal, whereas adult rumi nants can only be enriched significantly with polyunsaturated fatty acids (PUFA) by manipulation of diet composition (Jakobsen, 1999;Voigt and Hagemeister, 2001).Although animal and epidemiological studies have implicated dietary fat as a factor in cancer, recent prospective epidemiological data in humans have cast doubt on the possibility of a strong relationship.In summary, clear evidence points to the need to reduce intakes of saturated fatty acids in the diet (Grundy, 1999).
The objective of the experiment was to determine the effect of supplementing lamb diets with fats of different vegetable origin on fatty acid composition in the produced meat.

MATERIAL AND METHODS
The experiment was carried out on 24 lambs fattened from 22 to 40 kg body weight.The animals were divided into four groups and fed a basal diet consist ing of meadow hay and concentrate (60:40) fed ad libitum to the control group; the concentrate for the experimental groups was supplemented with 6% of lin seed oil, rape seed oil or hydrogenated rape seed oil in dry matter (Table 1).All animals had free access to water.Ill At the end of the fattening period, the lambs were slaughtered and the con tents of individual fatty acids in the longissimus dorsi muscles of the lambs were determined using the HPLC procedures of Heinig et al. (1998), modified by Czauderna et al. (2001).
The obtained data were analyzed using SAS procedures (User's Guide, 1990).

RESULTS
Feeding 6% of linseed oil, rape seed oil or hydrogenated rape seed oil to lambs had no significant influence on total saturated fatty acid (SFA) content, although a decreasing tendency was observed when linseed oil and hydrogena ted rape seed oil were added.Treatment effects on fatty acid composition of meat are shown in Table 2. Addition of 6% hydrogenated rape seed oil decreased (P<0.05) the level of miristic acid in lamb meat.Linseed and rape seed oils also decreased the level of miristic acid, but differences were not significant.Addi tion of rape seed oil increased (P<0.05) the level of stearic acid in comparison with groups that received linseed or hydrogenated rape seed oils.We also ob served significant (PO.05,PO.01) increases in total n-3 PUFA in meat when rape seed or linseed oils were added to the diet in comparison with the control group.Rape seed oil also caused a significant (PO.01) increase in total n-6 PUFA.

DISCUSSION
Fat modification promises success as a preventive measure.The extent of atherosclerosis and cardiovascular disease is related to the intake of fat and cho lesterol.In particular, the amount of fat containing saturated fatty acids in the diet correlates more strongly with the incidence of cardiovascular disease than total fat intake (Windier, 2000).Although differences in total SFA when fat was added to sheep diet were not statistically significant, we noticed a decreasing tendency of total SFA content.Modification of meat fat to contain n-3 fatty acids has potential for improving consumer health.In the conducted experiment, in creased concentrations of beneficial fatty acids in meat fat were obtained by feeding diets with rape seed or linseed oils.Differences in the effects of the added fats underscore the difficulties in understanding the effects of dietary fat on the fatty acid composition of fat deposited in muscles.Altering the composi tion of ruminant fats is difficult because of the hydrogenation of unsaturated fatty acids by microbes in the rumen (Harfoot, 1981).In the experiment of Stan ford et al. (1999) lamb fatty acid composition was markedly influenced.Satura ted fatty acids were reduced and PUFA were increased by increasing the amount of canola seeds in lamb diets.Conflicting results were obtained by Solomon et al. (1991).In their study, adding 6.5% whole rape seed to lamb diets increased the total level of SFA.The results of the present study demonstrate that the addi tion fats to lamb diets alters fatty acid composition, with potential benefits to human health.

TABLE 2
Fatty acid content in M. longissimus dorsi of sheep fed diets supplemented with different vegetable origin fat, u;g/g of lyophilized samples