By Brianna Isenberg and André Brito, University of New Hampshire
Demand for organically produced milk has been increasing in the U.S. over the last 10 years. As consumers become more health conscious and environmentally aware, focus has shifted to ways to naturally enrich foods to create value-added products while reducing the carbon footprint of dairy systems.
Including ground flaxseed as a dietary component for organically managed cows may have a three-fold benefit of providing a nutritionally enriched product to the con- sumer, increasing profitability for the farmer, and reducing enteric methane production thus minimizing the impact of dairy systems on the environment.
Flaxseed is an oilseed rich in fat, making it an excellent energy source. It contains high levels of the omega-3 fatty acid α-linolenic acid, which is transferred to milk fat. Feeding flaxseed also increases the concentration of conjugated linoleic acids (CLA) in milk. Both omega-3 fatty acids and CLA have been linked to potential health benefits to humans. Specifically, these bioactive fatty acids may reduce the incidence of chronic conditions such as cardiovascular diseases and cancer. Milk fat is the most variable component in milk, and feeding flaxseed provides a unique opportunity to match milk fatty acid composition to benefit human health.
Milk produced from dairy cows on pasture has a higher concentration of omega-3 fatty acids and CLA as compared to cows receiv- ing TMR. However, there are two major challenges to maintaining elevated levels of omega-3 fatty acids and CLA year-round: cows do not have access to pasture during the winter in northern climates; and, botani- cal composition of pastures varies throughout the grazing season, which can lead to fluctuating levels of omega-3 fatty acids and CLA in milk.
Diets supplemented with flaxseed, particularly when it is ground, also offer a unique opportunity to mitigate enteric methane emissions in dairy cows. Enteric fermentation from ruminant animals, particularly cattle, has been cited as the second largest source of methane emissions in the country. Methane is a potent greenhouse gas directly tied to global climate change. In addition, methane production represents a 2 to 12% loss in animals’ energy intake, which varies based on the level of feed intake and composition of the diet. In general, pasture- or high forage- based diets often lead to higher levels of methane production as compared to high grain-based diets or diets containing feeds rich in oil.
Focus of Studies
Several studies to improve milk omega-3 fatty acids and CLA through flaxseed supplementation and extension of the grazing season have been done as part of a four-year project funded by the USDA-NIFA-Organic Agriculture Research and Extension Initiative (OREI). Flaxseed supplementation was initially explored in vitro using laboratory artificial rumens at the USDA- ARS Pasture Lab in University Park, Penn. in a study led by Dr. Kathy Soder (Soder et al., 2012). The artificial rumen environment was created by obtaining rumen fluid from a donor cow and maintaining the fluid under anaerobic conditions. The artificial rumens were ‘fed’ diets in which orchardgrass pasture was replaced by increasing levels of organically grown, full fat ground flaxseed.
Flaxseed was provided at the following doses:
0, 5, 10, or 15% of the total diet dry matter. As flaxseed replaced pasture, apparent digestibilities of dry matter, organic matter, and fiber decreased linearly possibly as a result of the toxic effects of flaxseed oil on microbes that digest feed nutrients. However, methane production also decreased linearly as pasture was replaced with flaxseed likely as a result of reduced nutrient digestibility or inhibition of rumen microbes (i.e., methanogens) that produce methane or both. The first animal study conducted at the University of New Hampshire Organic Dairy Research Farm (UNH-ODRF) took place in the winter of 2012 and lasted 84 days. The objectives of the study were to investigate the impact of full fat, ground flaxseed on milk production and composition, milk fatty acid profile (e.g., omega-3 fatty acids and CLA), and methane emissions in organic Jersey cows.
The 20 Jersey cows used in the study averaged 937 lbs. of body weight and 111 days in milk in the beginning of the study. Sixteen out of the 20 cows were used to measure enteric methane emissions using the sulfur hexafluoride tracer technique. All cows were fed TMR containing (% of diet dry matter): 1) 55% alfalfa-grass bale- age, 8% grass hay, 6% soybean meal, 2% roasted soybean meal, 27% corn meal, and 2% minerals and vitamins; 2) 55% alfalfa-grass baleage, 8% grass hay, 5% or 1.85 lbs. ground flaxseed, 4.8% soybean meal, 2% roasted soybean meal, 23.3% corn meal, and 2% minerals and vitamins; 3) 55% alfalfa-grass baleage, 8% grass hay, 10% or 3.5 lbs. ground flaxseed, 3.5% soybean meal, 2% roasted soybean meal, 19.7% corn meal, and 2% minerals and vitamins, or 4) 55% alfalfa-grass baleage, 8% grass hay, 15% or 5.3 lbs. ground flaxseed, 2% soybean meal, 2% roasted soybean meal, 16% corn meal, and 2% minerals and vita- mins. Cows were maintained in a bedded-pack barn with dried pine shavings as bedding and fed individually using electronically recognition feeding doors.
As the percentage of flaxseed in the diet increased, cows’ dry matter intake decreased. Diets high in fat generally interfere with normal rumen function resulting in intake depression. In fact, dry matter intake decreased from 37.3 to 35.5 lbs./day in cows fed TMR containing 0% flaxseed (3.8% crude fat) or 15% flaxseed (7.4% crude fat), respectively. Milk production also showed a linear decrease averaging 46.7, 46.3, 45.4, and 43.9 lbs./day for cows receiving 0, 5, 10, and 15% flaxseed, respectively. Similarly, yields of milk fat (from 2.16 to 2.05 lbs./day) and milk protein (from 1.61 to 1.46 lbs./day), and MUN (from 12.8 to 10.9 mg/dL) decreased linearly in cows fed increasing levels of flaxseed. Linear reductions in the yields of milk components are explained by the linear decline in milk production; the observed linear decrease in MUN was associated to intake of crude protein, which also exhibited a linear decline (from 6.8 to 6.5 lbs./ day) in cows fed incremental levels of ground flaxseed. It is important to note that the diet with 15% flaxseed resulted in the poorest production of milk and milk components.
Despite the overall decrease in milk fat yield, milk content of omega-3 fatty acids (from 0.74 to 1.42% of the total milk fatty acids) and CLA (from 0.55 to 1.08% of the total milk fatty acids) increased linearly in response to incremental levels of flaxseed. It is worthwhile to mention that the TMR with 15% flaxseed led to the highest contents of omega-3 and CLA in the milk fat. However, milk content of omega-3 fatty acids in cows fed 10% flaxseed was very similar to that of cows fed 15% flaxseed (i.e., 1.36 vs. 1.42% of the total milk fatty acids, respectively), indicating that 10% flaxseed can maintain high omega-3 fatty acids in milk fat with 1.3 lbs. reduction in milk production per day. In addition to animal performance and milk composition, methane production measurements were also done in our winter feeding study. As the amount of flaxseed in the diet increased, methane production decreased linearly (from 285 to 225 g/d) showing a positive impact of flaxseed on greenhouse gas mitigation.
The second animal study conducted at the UNH- ODRF took place during the 2013 grazing season and lasted 120 days (from June to September). In this grazing season study, 20 early to mid-lactation Jerseys averaging 900 lbs. of body weight received diets (pasture plus TMR) containing (dry matter basis): 0 or 10% ground flaxseed (3.5 lbs./day). Cows had access to paddocks containing grass-legume pasture mix for approximately 16 hours daily in a rotational strip grazing management system with a new piece of fresh pasture provided twice daily after each milking. Cows were milked twice a day and were offered TMR after each milking. Diets were formulated (dry matter basis) to contain 40% pasture and 60% TMR. The TMR was composed by grass-legume baleage, corn meal/soybean meal-based concen- trate, and liquid molasses.
Milk production reduced numerically by 1.1 lbs./ day in cows fed pastured supplemented with 10% flaxseed (39 lbs. of milk/day) compared to those fed pasture with no flaxseed (40.1 lbs. of milk/day). A similar numerical reduction in milk production was observed in cows fed 10% of flaxseed in our winter feeding study. Milk fat content (4.23 vs. 4.17%) and yield (1.68 vs. 1.65 lbs./day) as well as milk protein content (3.43 vs. 3.47%) and yield (1.36 vs. 1.35 lbs./ day) were very similar in cows fed no flaxseed vs. 10% flaxseed. Milk analysis of omega-3’s and CLAs has not been completed to date.
To measure breath methane and carbon dioxide emissions from grazing cows, we used a portable, automated system (The GreenFeed® system; C-Lock Inc., Rapid City, S.D.) consisting of air sampling and gas quantification modules powered by solar energy and mounted on a trailer. The GreenFeed system uses radio frequency identi- fication and controlled, automated release of an alfalfa pellet to reinforce voluntary visitations by individual animals several times throughout the day. The GreenFeed was deployed on pasture and moved to a new paddock following the cows’ access to a new piece of fresh pasture. Measurements of methane and carbon dioxide were obtained every time a cow visited the GreenFeed.
Preliminary analysis showed that methane emis- sions was not reduced in cows fed flaxseed during the grazing season. This lack of flaxseed effect on mitigating methane emissions disagrees with our previous studies in which methane emissions were reduced in experiments conducted in vivo (i.e., winter flaxseed experiment) and in vitro (i.e., the artificial rumen experiment). Differences in diets, forage species, and techniques used to measure methane emissions possibly explain the discrepancy between our grazing vs. winter study.
In summary, feeding flaxseed to organic dairy cows during the winter and summer seasons provides both exciting opportunities and major challenges for organic dairy farmers. The winter study results showed a positive impact of flaxseed on changing milk fatty acid profile towards more omega-3 and CLA, particularly in higher levels of dietary inclusion (i.e., 10 to 15% flaxseed). Another positive response was the reduction in methane emissions when flaxseed was fed in higher amounts during the winter season. Unfortunately, higher levels of dietary flaxseed did reduce production of milk and milk components.
Based on our collective results so far, it appears that 10% of dietary inclusion of ground flaxseed is the best compromise. We will be able to provide a more solid recommendation as more results from our grazing study emerge. The major determinants of flaxseed adoption in organic dairy farms will be the cost of flaxseed supplementation, future industry premiums for omega-3 and CLA enriched milk, and potential niche markets for value-added organic dairy products.
Brianna Isenberg is a graduate student in Animal Sciences teaching assistant , and Dr. André Brito (andre.brito@unh. edu) is an Assistant Professor of Organic Dairy Management at the University of New Hampshire (Department of Biological Sciences; Durham, NH). They acknowledge the USDA-NIFA-OREI for funding this research and collaborators Dr. Kathy Soder (USDA-ARS-Pasture Lab, University Park, PA) and Dr. Jana Kraft (University of Vermont; Burlington, VT).
March | April 2014