BY-PRODUCTS ▶▶▶
Both fishing by- catch at sea and waste after pro- cessing on land are discarded, wasting nutri- ents and leading to environmen- tal pollution.
was also better, according to the panellists who assessed the meat quality characteristics. A fishy odour is the main chal- lenge when high levels of fish feedstuffs are incorporated in diets. The researchers suggested that their present findings could be valuable because the addition of a fish silage: soy- bean mixture of up to 30% in the feed did not alter the sensory quality of broiler meat. Similar to the first study in Mexico, researchers at the Agricul- tural University of Norway also studied the effects of dietary fish silage and fish fat on the growth performance and meat quality of broilers (day-old to 35 days). The treatments were a control diet, two test diets with 50 g/kg fish silage and differ- ent levels of fish fat (6 or 8 g/kg), and two diets with 100 g/kg fish silage and higher levels of fish fat (8 or 10 g/kg). Five treatment groups were used to study meat quality: the con- trol diet and four test diets each containing 50 g/kg fish silage and different levels of fish fat (2, 9, 17 or 25 g/kg). An inclusion level of up to 100 g/kg diet, corresponding to 21% of the total protein, showed a positive effect on growth performance. This high inclusion level (100 g/kg fish silage and 10 g/kg fish fat) showed an improvement in growth rate and FCR of 8% and 4%, respectively.
32 ▶ ALL ABOUT FEED | Volume 29, No. 4, 2021
Be careful with fat In this study, dietary inclusion of fish fat reduced plasma lev- els of vitamin E and ceruloplasmin (which catalyses the oxida- tion of various substrates, such as amines and catechols), in- dicating that the use of high-fat fish by-products increases the antioxidant requirement of broilers. High levels of fish fat may reduce the sensory quality of broiler meat. In the Norwe- gian study, the researchers found amounts of 17 g/kg fish fat or more caused ‘off-flavours’ in meat. They suggested that fish fat levels below 10 g/kg in broiler diets should not cause flavour problems in broiler meat.
Nutritional variations Nutritional composition is an important factor in determining inclusion levels: fish silages show variations in nutrient com- position which are due to differences in the type of fish, by- catch or fish part that have been processed in the silage. However, when fed at optimum levels, fish silage improves the growth performance of broilers without compromising meat quality. Overall, fish silage offers a potential environ- mentally-friendly alternative to partial replacement of expensive feedstuffs such as soybean meal and fishmeal.
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