Ethanol co-product can replace soy in salmon diets, say researchers

An enhanced co-product of the United States ethanol industry could be successfully used as a replacement for soybean meal in feed for Atlantic salmon, scientists from the University of Idaho have concluded.

The researchers conducted a 12-week feeding trial to evaluate a corn (maize) fermented protein with solubles (CFPS), and found that it did not negatively affect the growth or feed utilisation of the fish.

Fish fed CFPS also had an increased total body protein content.

Gut health

Soybean meal is commonly used for feed due to its wide availability, highly digestible protein and energy content, balance of essential amino acids, and reasonable price, wrote the researchers.

But it also contains some antinutritional factors, and high dietary inclusion results in lower feed intake, reduced weight gain, and negative impacts on gut health and overall health condition of fish.

Continued expansion of global protein demand in human, aquaculture, and livestock sectors has further increased the demand and cost of soybean meal, resulting in a search for alternatives.

44 million tonnes

Corn fermented protein with solubles is derived from distillers dried grains with solubles (DDGS), a co-product from the US ethanol industry which has the capacity to produce more than 44 million US tons of DDGS annually. Corn is the most widely used feedstock for ethanol production in the US.

Although DDGS generally has a moderate crude protein content of 28% to 32%, a new commercial CFPS produced from DDGS has a higher amount of 52% dry weight, making it more suited as an alternative protein ingredient for aquafeeds.

It also contains more lysine, in addition to the yeasts used for the fermentation process, which are also rich in protein, B vitamins and β-glucans.

In the feed trial the researchers fed the fish diets in which soybean meal was replaced in percentages of 25, 50, 75 and 100% by the protein product. A control group was fed with a standard soy diet.

Body protein content

After the experiment, the final weight, the specific growth rate, the weight gain and the feed utilisation yields were not significantly different between the different treatments.

Among the results, the researchers evidenced an increase in the total body protein content in the groups fed with the fermented corn protein compared to the control, being significantly higher in the feed with 50% of the soy replaced with CFPS.

“The inclusion of fermented corn protein significantly increased lipid digestibility and the fish fed with percentages of 75 and 100% showed significantly higher values followed by the group with 50%. A significantly lower value was observed in the control group fish,” the authors noted.

With the exception of cystine, lysine, tryptophan, tyrosine, proline and taurine, all other measured amino acids were significantly influenced by soybean meal replacement in the diet, being higher with 50% replacement.

Enteritis reduction

The researchers did not observe negative effects on the intestinal morphological characteristics due to the fermented corn protein, and that according to the intestinal histopathological characteristics, the replacement with 50% would significantly reduce intestinal enteritis.

“Based on the overall findings, we can conclude that the evaluated fermented corn protein can be effectively used as a replacement for soybean meal in Atlantic salmon diets,” the scientists said.

Read the abstract of the study titled “Evaluation of a corn fermented protein with solubles (CFPS) as a complete soybean meal replacer in practical diets for Atlantic salmon (Salmo salar)”, here.