Casein silage as feed for salmonids

Abstract

Three experiments were carried out to determine whether the protein source raw casein is acceptable in feed for salmonids and if an inexpensive and efficient method of preservation could be found. In the first experiment a preliminary evaluation was made of the efficiency of certain acids in preserving undried casein. It was shown that casein could be acceptably preserved by acids, similarly to silage from fish and fish offal. In the second experiment casein was preserved by 2.0% ( w/w) formic acid or by 2.0% ( w/w) sulphuric acid plus 0.5% ( w/w) formic acid. The silages substituted half the amount of frozen fish as a source of protein in moist diets for salmon ( Salmo salar L.) and rainbow trout ( Salmo gairdneri Richardson). About 20% of the total protein in the feed came from acid-preserved casein. No negative effects on feed consistency, weight increase of the fish, fish health, fish chemical composition or organoleptic properties were observed. In the third experiment the apparent digestibility of the dietary protein was determined. It was higher for casein than for raw fish and binder meal, above 95%, and highest for casein preserved by sulphuric plus formic acid.