The nutritional quality of milk improved when fish oil or both fish oil and plant oil were added to the feed of lactating cows, according to the doctoral dissertation of Piia Kairenius, principal specialist at the Natural Resources Institute Finland (Luke).

Adding oil to feed also had an effect on ruminal lipid metabolism, changing the metabolism of fatty acids in the rumen, Luke said in an announcement.

The doctoral dissertation studied opportunities to alter the fatty acid composition of milkfat to improve human health, Luke said. Adding fish oil to the feed of lactating cows alone or together with plant oils increased the concentration of healthy polyunsaturated omega-3 fatty acids -- such as eicosapentaenoic acid, docosahexaenoic acid and docosapentaenoic acid -- in milkfat, among others. This is based on an increase in the ruminal outflow of monounsaturated and polyunsaturated fatty acids, which are beneficial to human health, Kairenius found. As a result, their concentration in milkfat will also increase.

At the same time, the synthesis of saturated fatty acids that have a negative impact on human health will decrease in the mammary gland.

However, fatty acids of fish oil and plant oil are modified by the biohydrogenation process in the rumen, increasing the proportion of long-chain trans-fatty acids transferred to milkfat, Kairenius said. These trans-fatty acids may have a positive or negative impact on human health because trans-fatty acids generated in industrial processes are known to increase the risk for cardiovascular diseases in consumers.

“The nutritional impact of the intermediates of long-chain trans fatty acids formed in ruminal lipid metabolism is not yet known, although some have even been found to have a positive impact,” she said.

According to Kairenius, it is important to understand the mechanisms that affect the composition of the milkfat of lactating cows and how the composition of milkfat can be altered by using different feeding strategies, for example.

“In developed countries, dairy products are a significant source not only of high-quality proteins and other important nutrients for humans but also of fat. This study aims to study the nutritional properties of milk, dairy products and meat, improve their quality and, therefore, improve the health of consumers,” Kairenius said.

Energy balance of cows

Before the studies conducted during her doctoral dissertation process, the biohydrogenation mechanisms of long-chain omega-3 fatty acids as a result of microbial activity in the rumen and the intermediates formed had not been studied by adding fish oil alone or in combination with plant oils to the feed of lactating cows, Luke noted.

The doctoral dissertation studied the impact of fish oil supplements and fish and plant oil supplements added to the grass silage-based diets of lactating cows on mechanisms that regulate the biohydrogenation of fatty acids in the rumen, according to the announcement.

Biohydrogenation is a process in which enzymes produced by microbes in the rumen convert unsaturated fatty acids in feed into hard saturated fatty acids through intermediate stages.

Changes identified in the metabolism fatty acid in the rumen did not have any impact on the total number or relative proportion of microbes participating in biohydrogenation in the rumen. Only the number of bacteria belonging to the Butyrivibrio genus decreased when large quantities of fish oil were added to feed.

“Based on the results, the studied microbes in the rumen alone cannot explain the changes identified in the biohydrogenation mechanisms of fatty acids in the rumen and in the amounts of fatty acids generated,” Kairenius said.

In the study, several previously unidentified intermediates of ruminal lipid metabolism were identified from the digestive tract of cows and from milk, such as long-chain trans-fatty acids, and these fatty acids were found to be associated with a decrease in milkfat synthesis.

A controlled reduction in the milkfat synthesis by means of feeding may reduce the transfer of energy to milk, which may improve the energy balance of cows during early lactation, when a considerable amount of the energy the cows obtain from the feed is consumed to produce milkfat, Kairenius explained.

“Feeding solutions that reduce the milkfat synthesis and have no impact on feed consumption or milk production improve the transfer of nutrients to other tissues. As a result, they could help to solve the health and fertility problems caused by a negative energy balance in lactating cows and, therefore, improve the longevity of cows,” she said.