UNIVERSITY PARK, Pa. — When it comes to supplementing the diet of laying hens with omega-3 fatty acids to enrich their eggs — making them more heart healthy for consumers — some supplementation is good, but too much is bad for the chickens and can negatively affect their egg production.

That’s the conclusion of a Penn State-led team of researchers who conducted a novel study using oil from a microalgae to supply omega-3 fatty acids. That microalgae oil contained a high level of docosahexaenoic acid, a very long-chain omega-3 polyunsaturated fatty acid, which has documented human health-promoting effects in the areas of cardiovascular disease, cancer risk, eye health and cognitive function in older, healthy adults. 

The research was unique because eggs produced by hens in the study were found to have extremely high levels of very long-chain omega-3 polyunsaturated fatty acid enrichment, according to team leader Robert Elkin, professor emeritus of avian nutritional biochemistry in the College of Agricultural Sciences. But findings of the study, recently published in the journal Poultry Science, clearly demonstrated that there are limits to supplementation.

“When feeding the hens heart-healthy omega-3s to enrich their eggs, if the level of supplementation is too high, the birds’ egg production will be severely curtailed and some will stop laying eggs,” he said. “That’s because egg yolk is essentially derived from compounds made in the liver and transported to the ovary. Omega-3s are known to inhibit the secretion of these yolk precursors — mainly triglyceride-rich very low-density lipoproteins — from the liver.”

This is why fish oil, a source rich in very long-chain omega-3s, is effective in lowering serum triglycerides in humans, Elkin added. "But in the case of the laying hen, some dietary omega-3 fatty acids is good," he said. "But too much is not so good.”

In the study, conducted at the Penn State Poultry Education and Research Center laying hen facility, 56 white leghorn hens were allocated to a series of dietary treatment groups receiving graded levels of the microalgae oil supplement for 28 days. Those corn-soybean meal-based rations ranged from a control group that consumed no supplemental oil to as much as 40 grams of oil per kilogram of feed (4% of the diet).

As a result of that dietary supplementation, some of the hens produced eggs with extremely high levels of very long chain omega-3 polyunsaturated fatty acids — an average of 266 milligrams per egg. That is more than half the Dietary Guidelines for Americans 2015-2020 recommendation that healthy adults consume 450 to 500 milligrams of very long-chain omega-3 fatty acids per day.

But hens fed the 40g/kg microalgae oil diet, which equated to a daily consumption of approximately 3 grams of docosahexaenoic acid per bird per day, had greatly reduced reproductive performance and altered ovarian morphology, with marked liver enlargement and greatly lowered plasma triglyceride levels. The high level of supplementation also caused sharply depressed expression of key genes involved in triglyceride synthesis and secretion in the liver. As a result, egg production and yolk weights were greatly reduced, and five of the eight hens entirely stopped laying eggs before the end of the study.

Elkin and colleagues also observed that when hens were co-fed an oil rich in oleic acid along with the high level of microalgae oil, all of the aforementioned negative effects were reversed. Although not commercially feasible because of the associated costs, Elkin said this novel finding was important for better understanding fatty acid nutrition and metabolism in laying hens.

The bottom line is that microalgae oil can greatly enrich eggs, but the researchers recommended that its dietary inclusion should not exceed 20 g/kg (2% of the diet). This would allow for near-maximal enrichment of egg yolk with heart healthy very long-chain omega-3 polyunsaturated fatty acids without impairing hen productive performance.

In this study, researchers used microalgae oil for the dietary supplement because it is very high in docosahexaenoic acid— almost half of the oil by weight — but other non-fish sources of omega-3 polyunsaturated fatty acids are currently being investigated for egg and poultry meat enrichment, Elkin pointed out.

“Such sources include microalgae biomass, flaxseed meal and flaxseed oil, echium oil and Ahiflower oil,” he said. “In addition, although they are not yet commercially available, researchers have genetically engineered crops such as canola and camelina to make them produce omega-3 fatty acids, which they normally wouldn’t.”

Fish oil is rich in omega-3 fatty acids but feeding laying hens or broilers fish meal or fish oil can impart a “fishy taint” to eggs and meat. So, attaining high levels of omega-3 fatty acids enrichment in a poultry product acceptable to consumers could be problematic, Elkin noted.

“Another reason why people are turning to alternative sources of heart-healthy omega-3s is because of concerns over the methyl mercury content of oily, or fatty fish,” he said. “The enrichment of poultry meat and eggs is one way to get omega-3s into the human diet without eating fish.”

The research findings should be of interest to producers of “designer eggs,” Elkin suggested.

“I chose to publish in Poultry Science because I thought it would reach the target audience of technical specialists, nutritionists and others in the industry,” he said. “I think people are looking at microalgae oil now as a source of omega-3 enrichment. But whether they use microalgae oil or some other supplement, this research should be a cautionary tale for them. They need to be careful of the levels they feed to avoid causing hens to go out of production.”

Contributing to the research at Penn State were Kevin Harvatine, professor of nutritional physiology; Ramesh Ramachandran, professor of reproductive biology; and Rebecca Bomberger, Abiel Haile and Evelyn Weaver, graduate students in the Department of Animal Science; and Ahmed El-Zenary, Department of Nutrition and Clinical Nutrition, College of Veterinary Medicine, University of Sadat City, Egypt.

This work was supported in part by a grant from the Pennsylvania Poultry Industry Egg Research Check-Off Program.