Preparation of silage from Spanish mackerel (Scomberomorus maculatus) and its evaluation in broiler diets

The aim of the present study was to prepare silage from whole Spanish mackerel, which is one of the cheapest commercial fish, and an under-utilized species found on both the Pacific and Gulf of Mexico coasts. Chemical and biochemical changes during the silage process: pH, total nitrogen (TN), non-protein nitrogen (NPN), lipid oxidation, and trimethylamine (TMA) generated were monitored. The effect of ter-butylhydroquinone (TBHQ) as antioxidant under mechanical stirring and stabilized temperature was also observed. The liquid silage obtained was mixed with sorghum (1:2w/w), and dried in the sun. This silage-sorghum flour was used to prepare five diets with different silage-sorghum mix inclusions, and evaluated in a 21d feeding trial with broilers. During the silage process the NPN increased significantly by 85% from the original total nitrogen at 96h. The protein content in the dried silage and in the silage-sorghum mix was 653 and 169gkg⁻¹ on a dry matter basis, respectively. Minerals were found in high concentration in both fishmeal and silage, since the whole fish with bones and scales was used to prepare the silage, being Ca and P, which were at a higher concentration. Trp was the AA most affected by the silage process. Its concentration in the silage was decreased by 54% compared to that of fishmeal. However, the addition of sorghum supplemented the deficiency of this amino acid in silage. Most of the fatty acids were protected by the antioxidant and the ratio PUFA (poly unsaturated fatty acid) n-3/n-6 in fishmeal and silage was 4.7 and 4.9, respectively. In the feeding trial, no differences were found between the weight gain and feed conversion of the control diet and the four diets prepared with increasing amounts of silage-sorghum mix (P<0.05). It can be concluded that silage-sorghum mix is a good alternative to use as fish wastes or undesirable marine species in poultry feeding. The process does not require sophisticated equipment and the environment is protected.