The novel method of fortification did not affect the taste or smell of the milk, they add.
The study, published in a recent issue of the British Journal of Nutrition(2004, vol 91, no 2, pp 271-278(8), is the latest research to demonstrate increasing attention being made to livestock supplementation in order to improve human health.
Researchers in Spain are also working to boost levels of the omega-6 fatty acid, CLA, in lamb through changes to the animal's diet.
The team from the university of Sydney divided 14 cows in early lactation into two groups. While in individual stalls after each morning milking, one group was offered a mixture of rumen-protected tuna oil and soya in a supplement and the second group acted as control. Both groups grazed together on a spring pasture after supplementation.
Milk from the supplement group saw concentrations of EPA and DHA rise from undetectable levels to 6·9g and 10·1g per kg of milk fat respectively. Total omega-3 PUFA concentration in milk fat was increased three- to fourfold by tuna-oil supplementation (8·4 to 32·0 g/kg milk fat).
Meanwhile there were no significant effects on milk production, milk protein or milk fat in the supplemented group. The concentration of total saturated fatty acids in milk fat was significantly reduced (568 v 520g/kg total fatty acids) and there was a 17 per cent reduction in the atherosclerotic index of milk after tuna-oil supplementation.
The researchers asked 61 untrained consumer panellists to assess milk from both groups of cows for taste and smell and concluded that there was no change to the sensory characteristics of milk.
Demand for omega-3 fatty acids has surged in recent months on the back of increasing scientific evidence for its health benefits. Studies show that intake of these fats can significantly reduce the risk of heart disease and related cardiovascular events. Omega-3 fatty acids also play an important role in mental health - they are increasingly added to infant formula to promote brain development - and evidence suggests that they could reduce risk of Alzheimer's disease.
However omega-3s are produced in biggest quantities from fish oil and this tends to present taste and formulation issues when adding to foods. Companies are increasingly looking at alternatives to fish oil, such as the vegetarian options offered by Martek and Nutrinova derived from microalgae. Irish firm R Craig & Sons Ltd has recently filed a novel foods application for use of ground Chia seed, a rich source of omega-3 fatty acids, in bread.
UK supplement company Cultech has developed an emulsified fish oil powder, produced using a freeze-drying process, that it claims offers greater stability and longer shelf-life over oils. The product can also be added to a wider range of applications and early tests suggest the DHA and EPA in the powder could be more bioavailable than in the original oil form.