Utilization of Fish and Animal Byproducts in Mink Nutrition

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Abstract
Commercially available byproducts from the Norwegian cod (Gadus morhua) and haddock (G. merlangus) fisheries (fillet cuttings, filleting scrap, fish heads and filleting skin), were investigated in terms of proximate composition, amino acid pattern and performance achieved when applied at varying levels of protein in mink diets. Body growth and fur quality characteristics of mink kits were studied in 3 experiments involving 34 diets and 1870 animals. The diets were fed ad lib during the post-weaning growing-furring period, starting at June 15-July 3 and terminating at pelting in late Nov. or early Dec. With regard to 23 of the experimental diets, digestibility and N retention were determined using 4 male kits per treatment group. Fish byproducts originating from different parts of the fish revealed characteristic differences in proximate and amino acid compositions. Except from an adverse effect of filleting skin, the different fish byproducts did not appear to promote extensive differences in N retention. Data on body growth indicated that diets containing a conventional mixture of protein sources were slightly superior to those based solely on fish byproducts. Among fish byproducts, fillet cuttings tended to yield better growth than filleting scrap. If the protein requirement was met, partial replacement of filleting scrap with fish heads appeared to improve body growth. Filleting skin caused substantially poorer growth than any other fish byproduct. This effect could to some extent be counteracted by increasing the level of protein. When protein levels were reduced below approximately 7.5 g ADP/100 kcal ME [metabolizable energy] N balances of male kits tended to decline with decreasing protein concentration. The protein needs of the growing male mink exceed slightly those of the female. Regarding body growth and livability of male kits, 6 g ADP/100 kcal ME appeared to be borderline or suboptimal depending on protein quality and probably the source of non-protein energy. Little or no advantage appeared to be obtained by using more than about 7 g ADP/100 kcal ME. The evaluation of different fur quality characteristics revealed minor and inconclusive effects of treatment factors.