Apparent availability of zinc, selenium and manganese as inorganic metal salts or organic forms in plant-based diets for Atlantic salmon (Salmo salar)

Abstract

The composition of salmonid diets has changed from the use of mainly marine ingredients to increased use of plant ingredients, and this has an impact on the mineral content and availability. Minerals, like zinc (Zn), selenium (Se) and manganese (Mn), are supplemented to diets as inorganic or organic forms to cover the nutritional requirements of fish. This study compared the apparent availability (AA) of Zn, Se and Mn from inorganic metal salts and their organic forms in Atlantic salmon. Sixteen diets were prepared based on a two-level factorial design (24). The tested factors were Zn additive source (A), Se additive source (B), Mn additive source (C) and phytic acid level (D). The diets were fed to Atlantic salmon for 11 days, faeces were collected by stripping, and the total content of mineral and yttrium in diets and faeces were determined by inductively coupled plasma mass spectrometry. Data obtained were used to estimate the AA for the minerals. Zinc additive source had no significant effect on the AA of Zn. However, the Se and Mn additive source had significant effects on the AA of Se and Mn, respectively. Higher AA of Se was achieved with selenomethionine than with selenite, and Mn sulphate was more available than Mn chelate of glycine. The phytic acid level did not significantly affect the AA of Zn, Se or Mn. However, several interactions between mineral additive sources and the phytic acid level significantly affected the AA of Zn, Se and Mn.