Digestibility by mink and storage stability of feedstuffs made from raw ground, acid-treated or fermented dogfish (Squalus acanthias)

Abstract

Dogfish was evaluated in a 3 × 4 factorial design experiment conducted to determine digestibility coefficients (DC) of dry matter (DM), crude protein (CP), crude fat (CF), gross energy (GE) and amino acids (AA) in raw ground dogfish (RGD), acid (ASD) and fermented (FSD) dogfish silages for mink. The ASD was prepared with the addition of 2.5% (wt:wt) formic acid (conc. 85%) and 200 mg kg−1 antioxidant (ethoxyquin) to the raw ground fish. The FSD was produced with the addition of the commercial biopreservative Marisil®, (Finn Sugar) (1%) and extruded wheat (15%) to the raw ground fish. In the digestibility trial, consisting of three, 11-d periods, each having a 6-d adjustment followed by a 5-d collection, 12 mature standard type mink were confined to metabolism cages. Using the total collection (TC) method, where graded levels (0, 15, 30 and 45%) of the test feedstuff were substituted into a basal diet, an extrapolation using regression analysis was done to estimate digestibility of each test feedstuff. The AD of DM, CP, CF and GE was RGD: 81.8, 92.2, 96.2 and 89.6%; ASD: 87.1, 92.6, 100.0 and 93.2%; FSD: 86.0, 93.3, 98.1 and 90.4%, respectively. The AD of AAs was generally highest in the fermented dogfish feedstuff. A quality evaluation of the silages was conducted in a completely randomized design with four replications (two replications for AAs), to determine storage stability of the silages, on 10 different sampling days (days 1, 3, 6, 9, 15, 30, 90, 180, 270 and 360), (three sampling days for AAs) post-manufacture. The ASD was stable up to 180 d, after this storage time it underwent increases in pH and total volatile nitrogen (TVN) and decreases in N and AA content. The preservation of dogfish with a fermentation method (FSD) was judged to be unsuccessful with this feedstuff having a high initial pH (6.4) and large increases in TVN content early in storage. It was concluded that feedstuffs made from dogfish would provide a source of highly digestible nutrients for mink; however, more research is required before a fermented dogfish feedstuff can be incorporated into practical mink diets. Key words: Apparent digestibility, dogfish, fish by-products, mink, silage, silage quality