Effects of repeated gestation and lactation on milk n-6 fatty acid composition in rats fed on a diet rich in 18:2n-6 or 18:3n-6.

The present study examined the effect of repeated gestation and lactation on the levels of long-chain n-6 polyunsaturated fatty acids in rat milk fat, and examined whether such levels might be modulated by supplementing the diet of the lactating dams with either (g/kg) 50 safflower oil (SFO; containing 800 g 18:2n-6/kg), or 50 evening primrose oil (EPO; containing 720 g 18:2n-6 and 90 g 18:3n-6/kg). The milk was collected at three different times (days 1, 8 and 15) in each given lactation period from female Sprague-Dawley rats which were successively bred for four pregnancies and lactations. Results showed that dietary fat and breeding frequency had no significant effects on milk triacylglycerol content, but they modified the pattern of milk fatty acids in both triacylglycerol and phospholipid fractions. After three or four successive breedings rats fed on EPO produced milk containing less saturated but more monounsaturated and polyunsaturated fatty acids compared with those fed on SFO. During the course of lactation the levels of n-6 metabolites, e.g. 18:3n-6, 20:3n-6 and 20:4n-6, in milk fat declined progressively. However, they were consistently higher in the EPO group than in the SFO group. These findings suggest that the levels of long-chain n-6 metabolites in the milk fat may be increased through supplementing the maternal diet with 18:3n-6.