- Animals: poultry
- Animal Production: feed/forage, feed rations, free-range, housing
- Crop Production: cover crops, crop rotation, nutrient cycling, tissue analysis
- Education and Training: demonstration, on-farm/ranch research
- Farm Business Management: agricultural finance, new enterprise development, value added, whole farm planning
- Production Systems: holistic management, integrated crop and livestock systems, organic agriculture
In this project, we worked to develop key elements of a Purslane – laying hen system for production of high quality omega-3 fatty acids that are important in human nutrition. We defined phenotypic variation in growth, yield and concentrations of α-linolenic acid (ALA). We also documented a strong fertilizer N response with selected Purslane varieties. Purslane is currently being fed to free-range laying hens to determine the extent that DHA content is altered. Additional experiments are examining purslane tolerance to drought conditions and its tolerance to water stress.
The purpose of this project is to develop a low-input, sustainable agricultural system that will open the fast-growing omega-3 market to small farmers in the Southeast. The system involves growing the native plant common purslane (Portulaca oleracea L.) that is well adapted to the southeastern environment and was recently found to have omega-3 concentrations that are among the highest of any known plant species. The purslane will serve as a feed source for free-range laying hens that will, in turn, produce eggs with elevated, high quality omega-3s for human consumption. The omega-3 market is already established and rapidly expanding, and thus offers an excellent economic opportunity for small farmers.
Omega-3 fatty acids are now widely recognized as an essential component of human nutrition. They play an integral role in fetal brain development, mental health, cardiovascular function, retina function, gene expression, inflammation responses, and insulin sensing (6-21). Omega-3 fats are considered essential fatty acids because they cannot be produced by human metabolism. They must be acquired from food.
Currently, the diet of most Americans does not include adequate amounts of DHA (docosohexaenoic acid) (22). Plants produce 18:3 short-chain omega-3s (ALA, α-linolenic acid), which are poorly utilized by the body and contribute only marginally to human nutrition. The essential source for humans is the longer chain 22:6 DHA omega-3 form. Importantly, some animals, including poultry, can efficiently make DHA by lengthening ALA omega-3s originally produced in plants.
Historically, Americans obtained DHA from pasture raised animal products (23). This main source of omega-3s has been lost as the U.S. shifted towards confinement animal systems with mainly grain feed, which has low omega-3 levels.
There are problems with the two major sources of DHA in the Western diet, and neither of the sources are sustainable. Fatty fish are a main source of DHA. However, fish require processing and long distance transport with considerable transportation cost and the associated generation of greenhouse gases. Also, increased fish consumption is leading to rapid depletion of ocean fish populations (24). Perhaps most importantly, fatty fish are increasingly contaminated with heavy metals which are known to cause human health problems, particularly in young children. Heavy metal exposures can result in brain damage during pregnancy and the neonatal stage (14,16,25). The potential damaging effects thus coincide with the period with the most intense requirement for omega-3s, when much brain development occurs (6,9-10,12,14,16,25). The possible alternative of fish farming, where heavy metal accumulation might be minimized and natural populations protected, has also raised serious concerns because of environmental pollution and antibiotic resistance (26).
Flax seed is the second major source of omega-3s in Western diets. Unfortunately, production is confined to the upper mid-west climate (27), so there are substantial economic and environmental costs in transportation to the Southeast and other regions in the U.S. Feeding flax to chickens does increase the DHA concentration in egg yolks (28), but this is done mainly in large industrial farms. In those operations, conditions generally dictate that laying hens have little or no access to outdoors or room to express natural behaviors, and chicks typically are debeaked to prevent pecking other hens to death (29). Also, phosphorus and nitrogen originating from large industrial poultry operations are primary contributors to eutrophication and degradation of water resources (30).
The dietary importance of omega-3s and the problems with existing DHA sources strongly support the need for local sources.
Plants are the primary producers of omega-3 fats in terrestrial ecosystems. Omega-3s are mostly concentrated in thylakoid membranes of chloroplasts in plant leaves and in seeds of some species. Almost all omega-3 fatty acids in plants exist as short chain ALA.
Purslane is an excellent source of ALA, with levels that are among the highest found in the plant kingdom up to this time (1,2). Consistent with this contention, recent analyses done in an associated SARE Graduate Student Research Project revealed that ALA accounted for 60-67% of the leaf fatty acids and 26-29% of seed fatty acids in purslane.
Purslane is well adapted to the climate and soils in the Southeast and grows widely as a weed throughout the region. Compelling evidence for adaptation is the pervasiveness of purslane as a problem weed in multiple horticultural crops (31,32). The advantageous physiological mechanisms are somewhat obscure at this time, but several favorable properties are evident. Purslane reproduces indeterminately, so it continually generates seeds and has a substantial amount of reproductive elasticity. Furthermore, drought is one of the biggest problems encountered in southeastern agriculture. Field observations (33) and our preliminary studies indicate that purslane continues to grow and reproduce efficiently under drought conditions that adversely impact vegetable and crop species. And when extreme drought causes defoliation, eventual rainfall results in new shoot development from nodal tissues within days, and new growth and seed production follow.
A unique physiological property of purslane, and one that underscores its uniqueness, is that purslane evidently shifts between C4 and CAM metabolism. The shift depends on nutrient and water availability, making it highly adaptable to a range of environmental conditions (34,35). Under optimal growing conditions with sufficient water, as usually occurs in spring, purslane functions as a rapidly growing C4 plant. When conditions become dryer, as they often do later in the summer, CAM metabolism results in enhanced water use efficiency.
The rapid growth rates, apparent stress tolerance, and reproductive plasticity of purslane make it, potentially, an excellent forage crop. Importantly, preliminary studies indicate that free-range laying hens preferentially eat purslane growing in fields of mixed vegetation and purslane seeds mixed into hen feed. This dietary linkage with poultry is critical for the success of the DHA omega-3 generation system.
Purslane contains ALA omega-3 fatty acids, but the form of omega-3 fatty acids most important to humans is DHA. Humans can obtain DHA in two ways. One is to consume ALA and elongate it metabolically to DHA. However, the enzyme involved in the elongation reaction is functionally inefficient. It also elongates omega-6 fats, which are far more prevalent in the Western diet than ALA omega-3s. Because of enzyme competition and internal catabolism, it is estimated that less than 15% of consumed ALA is converted to DHA in humans (6). As evidence of the problem, nursing women consuming only ALA have drastically lower DHA in their breast milk than women who consume DHA (6).
The second way humans can obtain DHA fatty acids is by consuming DHA directly. Within a nutritional perspective, even though animals such as chickens cannot produce omega-3 fats, they can convert dietary ALA from plants into DHA. It has been repeatedly shown that laying hens fed high ALA diets produced eggs with high DHA yolks (4-5,28). The eggs thus become an inexpensive and concentrated source of DHA for humans.
Raising chickens in open pastures offers benefits over large vertically-integrated commercial systems. Under the integrated contracts, farmers must take out large loans to build expensive buildings. In contrast, free-range rotations have low up-front costs. Production on a relatively small area of land can be maximized by properly rotating plots. Plus, raising chickens on open pasture cycles nutrients and reduces the need for antibiotics and coccidistats because UV light kills nearly all chicken pathogens (36). And importantly, free-range, high omega-3 eggs have a market value that is markedly higher than that of typical, local free-range eggs.
One of the most challenging aspects of the movement towards sustainability is to integrate plant and animal systems in a profitable, environmentally sensitive manner. The purslane/poultry system will accomplish that. With purslane serving as a key food component for the free-range hens and the hens providing fertility for the purslane, the system cycles nutrients and minimizes the need for external inputs. With appropriate purslane acreage and poultry populations, it also can be optimized for nutrient cycling and nutrient containment to minimize environmental degradation.
The elevation of omega-3 levels will add value to free-range eggs. Based on the premium for high omega-3 eggs currently sold in supermarkets, along with the relatively low cost for establishing purslane, high omega-3 free-range eggs should generate higher profits for small farmers.
Another significant feature of the purslane/poultry omega-3 generation system is the production of a nutrient that is essential to human health but currently deficient in the diet of people in the U.S. While the shift to large-scale, commercial production of meat and dairy products can be justified in economic terms, it does come with costs – the loss of dietary omega-3s being one. Individual and community health benefits from having a local, readily available, lower cost supply of omega-3s could be considerable.
A compelling aspect of the purslane/poultry system is that we know it can work. Field observations over the past decades, recent preliminary experiments, and research literature provide concept proofs: 1) purslane is a rapidly growing species that is well adapted to the Southeast; 2) purslane has high ALA omega-3 fatty acids, 3) free-range chickens preferentially eat purslane vegetation and seeds, 4) a high ALA diet for poultry results in high DHA eggs, and 5) high DHA omega-3 eggs bring a market premium. The goal now is to assemble the sustainable integrated system, make it efficient, and maximize its profitability.
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1. Determine the variation in ALA omega-3 fatty acids in Purslane acquired from different sources and how best to conserve ALA in processing.
2. Determine alterations in ALA content in Purslane plants subjected to environmental stress.
3. Evaluate the potential for Purslane inclusion into the poultry diet and the effects of Purslane on
DHA omega-3 levels in eggs.
4. Examine the effects of Purslane inclusion in forage rotation on egg production and DHA
accumulation in eggs.
5. Determine the economic feasibility of the proposed production system.