| Summary: | As salmon aquaculture continues to grow, understanding aquafeed conversion is imperative for making informed strategic growth planning and management decisions. Accurately measuring the apparent digestibility (AD) of commercial aquafeeds on farms requires greater understanding and method development, including the validation of one or more inert endogenous AD markers. Laboratory and commercial experiments assessed the potential of elements that naturally occur in aquafeeds as potential endogenous AD markers. Two commonly used and validated AD markers, acid insoluble ash (an endogenous marker) and ytterbium oxide (an exogenous marker) were compared using protein AD calculated from a range of endogenous elements. Using a Percentage Similarity Analysis, comparison of protein digestibility calculated with recognised AD markers demonstrated lutetium (Lu) was the most accurate endogenous AD marker. Identification of Lu as an effective endogenous AD marker in commercial salmon aquafeeds will facilitate straightforward measurement of AD under commercial conditions. This work has important application in salmon aquaculture where protein AD is fundamental to growth efficiency.
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