The present study was conducted to determine the pattern of incorporation of dietary EPA and docosahexaenoic acid (DHA) into milk, and to evaluate consequent changes in milk fat composition and sensory characteristics. Fourteen multiparous cows in early lactation were divided into two groups and were offered supplements for 10 d. While individual stalls after each morning milking, one group was offered a mixture of rumen-protected tuna oil (RPTO)–soyabean supplement (2 kg; 30:70, w/w; +RPTO) and the second group was offered the basal ration without RPTO (−RPTO). Both groups grazed together on a spring pasture after supplementation. Feeding supplemental RPTO increased the concentrations of EPA and DHA in milk fat from undetectable levels in −RPTO cows to 6·9 and 10·1 g/kg milk fat respectively. Total n-3 PUFA concentration in milk fat was increased three- to fourfold by tuna-oil supplementation (8·4 to 32·0 g/kg milk fat). There were no significant effects on milk production (35·4 v. 33·9 l/d), milk protein (28·2 v. 30·1 g/kg) or milk fat (36·2 v. 40·4 g/kg for −RPTO and +RPTO respectively). The concentration of total saturated fatty acids in milk fat was significantly reduced (568 v. 520 g/kg total fatty acids) and there was a 17 % reduction in the atherosclerotic index of milk after tuna-oil supplementation. Untrained consumer panellists (n 61) rated milk from both groups of cows similarly for taste and smell. We conclude that it is possible to enrich milk with n-3 PUFA without deleterious effects on yield, milk composition or sensory characteristics.

The effects of different dietary essential fatty acids on piglet tissue composition at birth and performance until 7 days post weaning were investigated by offering the sow diets containing (17·5 g oil per kg diet) either maize oil (MO) as a control treatment, tuna oil (TO) as a source of long chain n-3 polyunsaturated fatty acids, particularly 22:6 n-3, or a mixture of maize and linseed oils (LO) which supplied the same amount of n-3 acids as TO but in the form of 18:3 n-3. Ten sows were allocated to each treatment which was offered throughout pregnancy and lactation. Compared with MO, offering TO increased sow plasma and subcutaneous adipose tissue 22: 6 n-3 proportions whereas LO increased 18: 3 n-3 and, to a much lesser extent than TO, 22: 6 n-3. Offering TO to the sow increased the proportions of 20: 5 n-3 and 22: 6 n-3 in piglet brain and liver at birth and decreased the n-6 acids, 20: 4, 22: 4 and 22: 5. LO only increased piglet liver 20: 5 n-3 proportions but to a lesser extent than TO; however, LO also decreased the proportions of 20: 4, 22: 4 and 22: 5 n-6 in piglet tissues. Offering the pregnant sow dietary 18: 3 n-3 therefore increased deposition of 22: 6 n-3 in foetal piglet tissues to a much lesser extent than tuna oil and so it is necessary to offer the sow pre-formed 22: 6 n-3 in order to achieve maximum foetal 22: 6 n-3 deposition. By experimentally allocating piglets at birth, effects of sow nutrition during pregnancy and lactation were separated. Piglets sucking MO or TO sows were heavier than piglets sucking LO sows 7 days post weaning.

To investigate whether long-chain n-3 polyunsaturated fatty acids could cross the porcine placenta in late pregnancy and alter neonatal piglet tissue composition, multiparous sows (seven per diet) were fed on diets containing a supplement (30 g/kg) of either soyabean oil or tuna oil for the last 21 d of pregnancy and the first 7 d of lactation. The proportions of all fatty acids, except 18:1n-7, differed between diets: in particular, the tuna-oil-containing diet supplied more 22:6n-3 and less 18:2n-6 fatty acids than the soyabean-oil-containing diet. The proportions of n-3 fatty acids, particularly 22:6n-3 (g/100 g total fatty acids) in sow plasma, colostrum and milk were increased and the proportion of 18:2n-6 was decreased by feeding tuna oil. Piglet tissue n-3 fatty acid proportions (particularly 22:6n-3), obtained shortly after birth, were increased in piglets born to tuna-oil-fed sows compared with progeny of soyabean-oil-fed sows. The increase in the proportion of n-3 fatty acids (g/100 g total fatty acids) in piglet tissues as a result of tuna-oil feeding, compared with soyabean-oil-feeding, was in the order plasma>liver>erythrocytes>spleen>brain>retina. Piglets born to tuna-oil-fed sows had a lower viability score at birth than the progeny of soyabean-oil-fed sows. The proportions of long-chain n-3 fatty acid in tissues of new-born piglets were increased by feeding tuna oil to the sow in late pregnancy; however no improvements in piglet viability were observed.