By Dr. Heather Darby, UVM Extension Agronomist and Nutrient Management Specialist
Added September 10, 2012.
There has been increasing interest by consumers to purchase livestock products that are enhanced in beneficial fatty acids such as omega-3. Omega-3 fatty acids are considered essential polyunsaturated fatty acids (PUFA). They are necessary for human and livestock health but the body can’t produce them and therefore we must get them through food. Numerous research studies indicate that omega-3 fatty acids reduce inflammation and may help lower risk of heart disease, cancer and arthritis in humans. Omega-3 fatty acids are also highly concentrated in the brain and appear to be important for cognitive (brain memory).
Maximizing omega-3 in milk and dairy products would benefit human health and nutrition. However, little is known about the effects of adding omega-3 PUFA to the diets of dairy cows. Such a practice may improve their immunity. Understanding how omega-3 PUFA affect the immune functions of dairy cattle may lead to the development of strategies that will decrease the incidence of diseases and improve reproductive efficiency. For example, Petit et al. (2001) reported increased first-service conception rates (87.5 percent versus 50.0 percent) in dairy cows fed omega-3 concentrates compared with dairy cows fed other sources of fat.
It is widely accepted that the humans should have the proper ratio of omega-3 and omega-6 (another essential fatty acid) in the diet. Omega-3 fatty acids help reduce inflammation, and most omega-6 fatty acids tend to promote inflammation. A diet that consists of one to four times more omega-6 fatty acids than omega-3 fatty acids is considered healthy (Daley et al., 2010). The typical American diet often contains 11 to 30 times more omega-6 fatty acids than omega-3.
In order to increase the levels of omega-3 in the diet humans must consume various products rich or enriched with these fatty acids. Omega-3 fatty acids are fats commonly found in marine and plant oils such as forages and flax. Interestingly fish are high in omega-3 because they consume marine plankton plants. Therefore in order to increase the omega-3 concentration in livestock products animals must be fed omega-3 rich feed sources. It has been documented that manipulating the diet of dairy cows can increase omega-3 PUFA and delivering this enhanced milk to consumers also resulted in a decline in human LDL-cholesterol levels (Noakes, 1996).
There are multiple means to manipulating the diet of a dairy cow to enhance fatty acid composition of milk. It is well documented that diets containing flaxseed or fish oil can increase omega-3 in the milk. However, since plants make up the majority of the organic cow dairy diet it makes sense to increase omega-3 in milk through forages. Enhancing omega-3 milk contents through forages would represent a more economical, practical, and sustainable source.
Crop management can have a major impact on levels of omega-3 PUFA in the forages.
Knowing how to best manage forages to maximize omega-3 will further increase the success of creating nutritionally dense milk products. There are many practices that have been documented to influence omega-3 concentration in forages. However, there are still many unknown factors that will require more research to maximize the potential to create nutrient dense forages and milk products.
Forage Species: There are differences in omega-3 concentrations amongst perennial forages species and cultivars (Bauchart et al., 1984). One study documented that annual ryegrass, orchardgrass, meadow fescue and tall fescue had higher omega-3 concentrations than timothy, Kentucky bluegrass, and bromegrass. Interestingly within a grass species there were major significant differences in omega-3 concentrations of cultivars. In terms of legumes, white clover had the highest concentration of omega-3 PUFA as compared to alfalfa, red clover, and birdsfoot trefoil. Cereal grains that can be used for extending the grazing season showed little difference amongst species in omega-3 concentrations in a study conducted at the University of Vermont.
Forage Storage: Fatty acid concentrations in some pasture can exceed 50 g/kg DM, depending on plant species, stage of maturity, fertility, and environment (Freeman-Pounders et al., 2009). Much lower concentrations are usually seen in hay and silage prepared from the same plant species (Boufaid et al., 2003). This is partially due to loss of plant leaves where chloroplast lipid is concentrated, but also due to plant metabolism of stored energy sources. Since many cows in the northeast are only grazed 6 months of the year, additional research needs to be conducted to develop strategies that would increase the omega-3 in stored forages.
Plant Maturity: Plant maturity has a definite impact on both fatty acid content and fatty acid composition. Fatty acid content (g/kg DM) generally is highest in the spring and fall seasons and lowest in the summer months. For example, fresh perennial ryegrass contained 32 g/kg DM total fatty acids during primary growth in May, but only 12 g/kg DM at the beginning of second regrowth (Bauchart et al., 1984). Recent research at the University of Vermont Extension has shown that omega-3 concentrations decline as forages become mature. This may indicate that timely harvest of stored feeds can help to elevate omega-3 concentrations.
Plant Fertility: Recent research has shown that nitrogen fertilization can substantially increase the concentration of omega-3 in perennial forages (Boufaied et al., 2003). This makes sense because there is a strong relationship between crude protein and fatty acid concentrations in permanent pastures. Recent research at UVM did not show an increase in omega-3 PUFA with increasing rates of various organic nitrogen fertilizers (Table 2). Further research is required to confirm the impact of nitrogen fertility and fatty acid levels in forages.
The ability to increase and sustain omega-3 concentrations in milk products may provide farmers with a higher value milk market and potentially improve farm economics. There are many practices that will influence the quantity and quality of fatty acids in forage plants. Since forages make up the largest percentage of organic dairy cow diets it makes sense to focus time and research on better understanding this topic. Current work at UVM will continue to develop strategies to assist farmers with enhancing these beneficial fatty acids in forages and also monitor changes in the milk concentrations. So stay tuned for more information on this subject matter!
References
Dr. Heather Darby is an Agronomic and Soils Specialist for the University of Vermont Extension. She is involved with implementing many organic research and outreach programs in the areas of fuel, forage, and grain production systems in New England. Outreach programs have focused on delivering on-farm education in the areas of soil health, nutrient management, organic grain and forage production, and oilseed production. Heather will be one of our featured speakers at the 2012 NODPA Field Days.
