I came across a very interesting paper by Margareth Øverland et al from the Aquaculture Protein Centre in Norway. It reviewed the possibilities of bacteria as feed ingredient for monogastric animals and fish. In particular, methane-using bacteria appear to be a sustainable alternative for current protein sources.
Bacterial (microbial) protein meal (BM) is a great product – it can be grown rapidly and may relieve the pressure on limited and expensive high quality protein sources like fishmeal. The use of microbial protein sources is not a new insight and several bacterial protein products have been tested since in feed trials - with promising results! But due to economical considerations related to increasing oil prices and the low price of conventional protein sources it never really took off. Times are different now and there is an increases demand for sustainable protein sources and alternatives for (mainly) fish meal. This has triggered renewed interest in the use of microbial protein sources for animal diets.
Production of bacterial meal
There are different technologies to produce BM. The current technology is based on bacterial fermentation using methane - the main component of natural gas, which is found widely in nature. The naturally occurring methanotroph Methylococcus capsulatus (bath) (pictured) has shown high efficiency in production of bacterial protein from methane. These types of bacteria only need methane as their sole source of carbon and energy for growth. The production of BM then goes as follows: the bath are added in a specially designed and patented loop fermentor that is continuously aerobe and contains 2 cubic meter of methane as carbon and energy source per kg of biomass dry matter. The bacteria develop quickly in the fermentor and the product can be harvested. Today, a number of products with specific characteristics have been developed including autolysates and autolysate extracts produced under high pressure and catalyzed by endogenous enzymes for example.
Nutritional value of the product
The nutritional value of bacterial protein sources depends on the growth media, the process of manufacture, and downstream processing. A number of recent studies looked at the nutritional value of different batches of bacterial meal, based on criteria such as chemical composition, effects on protein and energy metabolism, and growth performance and animal health in feeding experiments. It was shown that the digestibility of individual amino acids in BM varied considerably: high digestibility was found for lysine and arginine, while digestibility of cysteine was low. The digestibility of crude fat in BM was estimated at 87.2% in salmon and 90.5% in mink (unpublished data). When BM was added to diets for grower pigs, replacing soybean meal, there was a decrease in the digestibility of N, but digestibility of energy was not affected. BM in broiler diets - replacing soybean meal or fishmeal – did not affect or increased the digestibility of amino acids In both salmon and rainbow trout, the digestibility of most amino acids, fat and energy decreased with increasing dietary levels of BM replacing fishmeal.
What are the inclusion rates?
In general, results from the pig experiments suggest that BM can at least constitute up to 41% of the dietary protein for piglets and up to 44% for growing-finishing pigs without impairing growth performance. Studies with broiler chickens suggest similar feed intakes at levels of up to 14–17% of the dietary protein from BM and improved feed efficiency at levels up to 33%, but decreased weight gain at inclusion levels above 30% of the dietary protein, when replacing soybean meal. The results also demonstrated that BM can constitute up to 52% of the dietary protein replacing high-quality fishmeal in diets for carnivorous fish species like Atlantic salmon without adversely affecting growth, while rainbow trout and Atlantic halibut seemed to perform better at the lower inclusion levels of 38 and 13% of dietary protein from BM, respectively. But such high inclusion rates are not implemented in practice. Bacterial protein grown on natural gas was approved by the European Union in 1995 for use in pigs (max 8%), veal calves (max 8%) and salmon (max 33% for salmon in salt water and 19% for fresh water) (Council Directive No 82/471/EEC).
The future looks promising
The fact that bacterial protein can be grown rapidly without requiring a large physical footprint may relieve the pressure on limited and expensive high quality protein sources like fishmeal. It certainly is promising! A number of recent studies have confirmed the nutritional value of bacterial meal (BM), based on criteria such as chemical composition, effects on protein and energy metabolism, and growth performance and animal health in feeding experiments. Revision of the EU regulations concerning microbial protein sources (Regulation (EC) No 767/2009) may facilitate further development and use of such products as feed ingredients. Let's hope so!
[Original paper: Øverland, Margareth, Tauzin, Anne-Helene, Shearer, Karl and Screed, Anders(2010) 'Evaluation of methane-utilizing bacteria products as feed ingredients for monogastric animals', Archives of Animal Nutrition, 64: 3, 171 — 189, First published on: 10 May 2010 (iFirst)]