Two of the most essential protein sources to the animal feed industry - fishmeal and soy - are also two feed ingredients sometimes criticised as unsustainable.
Even those who fiercely defend the two industries will generally admit that a significant increase in output would require disrupting highly sensitive ecosystems from the ocean to the rainforests.
Therefore, it is widely accepted that the feed of the future will need to be able to draw on a much wider array of protein sources.
There are many of these available, ranging from legumes to animal byproducts. However, this article will focus on two of the less-well-understood sources of alternative proteins - algae and methanotrophic bacteria.
These two have the advantage of not pitting human consumption and animal feed consumption against each other, as neither is a primary source of calories for humans (unlike, say, wheat).
Moreover, their production would probably not require use of high value farmland.
Therefore, they may both have a part to play in helping us feed a growing world population on static levels of fertile land.
Algare actually a heterogeneous mix of organisms, and for feed purposes researchers are investigating a wide array, from single-celled microalgae, such as Chlorella, to macroalgae (seaweed) such as Ascophyllum nodosum.
Protein, fat and (carbohydrate) levels in various algae and crops
Spirogyra: 16-25, 11-21, (33-64)
Anabaena cylindrical: 43-56, 4-7, (25-30)
Chlorella vulgaris: 51-58, 14-22, (12-16)
Spirulina: 60-71, 6-7, (13-16)
Soybean: 37, 20, (30)
Corn: 10, 4, (85)
Wheat: 14, 2, (84)
Figures show % of dry matter. Source: FeedInfo
According to research by Stephen Bleakley and Maria Hayes, seaweed, at 2.5-7.5 tonnes per hectare per year, and microalgae, at 4-15 tonnes per hectare per year, have "higher protein yield per unit area", than conventional crops such as soybean, pulse legumes, and wheat.
These have protein yields of at best 2 tonnes per hectare (although total crop yield may, of course, be larger).
Spirulina algae have protein levels of 60-71 grammes of protein per 100 grammes.
Importantly, algae also generally contain all the essential amino acids, making them appealing replacements to proteins such as fishmeal, although in a literature review, Mark Wells and fellow academics point out that many nutritional factors of algae including amino acid levels may vary depending on the coastal conditions in which they are grown and the season in which they are harvested.
Moreover, beyond simply their high protein and interesting amino acid profile, algae also bring additional nutritional benefits.
Polyunsaturated fatty acids, including omega-3 fatty acids, vitamins, minerals, antioxidants, and natural colorants are all found at high levels.
Certain algae, such as Chlorella, have been determined to increase gut health and immune status too.
It has even been found that inclusion of seaweed into ruminants' diets can reduce methane emissions dramatically, hinting at a potential solution to reduce the greenhouse gas footprint of the livestock sector.
As photosynthesisers, algae also contribute to the fight against greenhouse gases by consuming carbon dioxide as they grow.
Indeed, Dr Matt Carr of the US's Algae Biomass Organization told Feedinfo News Service he believes these nutritional benefits can serve as a sort of stepping-stone to cost-effective high volume production.
"We've seen in the last 18 months to two years a real emergence of one particular algae feed ingredient, which I believe will be the tip of the spear in terms of bringing [algae] to mass markets, which is the omega-3 fatty acids."
He cautions that commercial production of algae currently is for high-value specialised feed ingredients rather than crude protein biomass.
However, Dr Carr predicts a trajectory for the sector which will see companies initially scale-up production in order to manufacture these expensive ingredients, but then move into the space occupied by higher-volume commodity feedstuffs once prices for algae production fall.
"We're seeing the move along that trajectory, which is quite promising.
"I think it's only a matter of time before we see broader adoption as an alternative to other feed commodities."
Having the incentive of high value payouts from specialty algal ingredients is necessary in order to face the considerable obstacles to the use of algae in feed.
One such obstacle is the requirement of complex processing in order to render algae digestible and their nutrients bioavailable.
According to Dr John Forster, "in the raw state, seaweed nutrients are protected by indigestible cell walls, or are chemically bound in a way that diminishes their potential nutritional value".
Bleakley and Hayes flagged studies that "appear to suggest that unprocessed seaweed proteins have reduced digestibility compared to that of other protein sources", adding that "improved extraction methods of cell disruption and extraction are therefore required" for commercial production.
Production of algae also presents challenges, whether it's a question of harvesting wild-grown sources or farming it in controlled conditions.
When it comes to harvesting seaweed, Bleakley and Hayes point out that the regulation of such activities remains in its infancy.
Technical advances are also required. In some geographies, or for some species, harvesting by hand remains the norm.
When it comes to farming microalgae in enclosed vessels, several problems arise. Ensuring all the organisms have access to light requires solutions such as turning or stirring the medium and preventing build-up on the containers' surfaces.
Meanwhile, farming in open ponds makes keeping out undesired species difficult, renders temperature control nearly impossible and thus often operates sub-optimally, and in many cases, consumes precious freshwater resources.
Harvesting the quick-growing crops is a nearly constant activity, and separating them from the growth medium requires significant inputs of energy.
These complications have traditionally made algae a solution that was difficult to ramp up.
However, Vitor Verdelho Viera, president of the European Algae Biomass Association, disagrees with the assertion that technology is still the factor limiting algae's growth as a feed ingredient.
"The 'biofuels from algae' phenomena that emerged 10 years ago pushed the technology and provided a wide range of solutions for the technology bottlenecks," he said in correspondence with Feedinfo News Service.
"At the moment, the main constraint is the investment in very large scale operations that can bring the costs down."
He argues that closed systems may be used to produce a continuous source of a stable inoculum (which can be conceived of as similar to starter seeds in greenhouses), then several open systems can be used for the large-scale production.
Bacteria are by far the most numerous lifeform on earth, outweighing both plants and animals.
Of course it is rare that they serve as the biomass for human foods, even though they are important to transforming many fermented foods.
However, at least one species, Methylococcus capsulatus, is being used as the basis for feedstuff by at least two companies, Calysta and Unibio.
Methylococcus capsulatus is a methanotroph, meaning it metabolises methane, a greenhouse gas that is produced by many sources but notably as a byproduct of the petroleum industry.
Therefore, bacterial protein from methanotrophs address two environmental problems at once, by consuming inputs that are climate-warming wastes and by producing valuable feed inputs for the animal production industry.
Beyond being a noble effort at capturing and transforming GHGs, bacterial protein is also a nutritionally robust source of protein, at least according to the companies manufacturing it - he feed products of both Calysta and Unibio advertise crude protein levels of over 70%.
Moreover, the amino acid profile is said to be superior to that of fishmeal.
According to Unibio, their Uniprotein has been tested as feed for salmon, calves, pigs, and chickens, while Calysta claims their Feedkind has been tested in salmon, trout, piglets and even pets who have proven sensitive to other feed ingredients.
But what of production?
Calysta currently operates a market introduction facility to produce sample quantities, and will be bringing a large-scale production unit online in Memphis, Tennessee in 2019.
The facility's initial capacity will be 20,000 tonnes annually, but the company foresees expanding that to 200,000 tonnes.
This site will feature 20 fermenters "each similar in size to a football field end zone," as well as "several kilometres of piping", according to the company.
Meanwhile, Unibio brought online a fermentation facility in October with a capacity of up to 80 tonnes and plans a second "full size commercial plant" later this year.
The company has also expressed interest in licensing its technology in order to make UniProtein production possible in a variety of locations where the natural gas that the product is built out of is currently going to waste.
Therefore, in spite of the novelty of the concept, at least two companies are powering ahead with large-scale production.
Moreover, Calysta's partnership by none other than agribusiness giant Cargill shows that at least one of the most influential names in animal nutrition is ready to take a chance on this concept.