Fish Silage

Key words Fish processing wastewater, post-coagulation sludge, fish silage. 

There are two possibilities dry feed - e.g., fish meal and liquid feed -e.g., fish silage (protein hydrolyzates) [7]. In this research the utilization of sludge for fish silage production has been investigated. 

Fish silage is produced in a way presented on these scheme [8] ... 

Fish silage is usually produced from fish offals (heads, intestines, skin, etc.) or waste fish. The enzymes present in fish viscera decompose these tissues and the liquid protein hydrolyzate is the final product [9-11]. To avoid bacteria growth a pH about 2 is required and a relevant amount of organic or inorganic acid is added, usually it is sulphuric acid. The idea was to supply a certain amount of post-coagulation sludge for silage production [12]. 

When the post-coagulation sludge is added to hydrolyzate production, then the iron hydroxide is converted into ferric sulfate, which is well soluble in water. Too high content of soluble iron compounds, which are easily absorbable, should be avoided, as the excessive amount of the iron in the diet is harmful [13]. It leads to some disease like hemochromatosis or siderosis. Thus, the aim of our research was to find a method of decreasing the absorbable iron content of fish silage. 

Asgard, T. and Austreng, E. (1981) Fish silage for salmonids a cheap way of utilizing waste as feed. Feedstuffs 53 22-24. 

In our experiments the coagulation of fish processing wastewater was performed using ferric sulfate. The sludge generated in this process has been added for silage production. The sludge characteristics are presented in Table 3. 

More dramatic inhibition of the reduction of trans-18 1 in the rumen was observed when fish oil was included in the diet (Wonsil et al., 1994). Studies have shown that feeding 250 g of fish oil/day to cows fed grass silage-based diets decreased ruminal outflow of stearic acid by 83% (Shingfield et al.,... 

The relationship between substrate and product for A-9-desaturase is reflected by the desaturase index, defined as [RA a- (RA + VA)]. Various approaches to calculating desaturase index in milk fat are discussed by Kelsey et al. (2003). In the study by Corl et al. (2001), the desaturase index was 0.23 for the hay and concentrate diet and 0.20 when the diet was supplemented with PH VO. Kay et al. (2004) reported a desaturase index of 0.25 for the pasture diet and 0.22 when the diet was supplemented with sunflower oil. Piperova et al. (2002) observed desaturase indices for highland low-fiber diets of 0.40 and 0.35, respectively. Shingfield et al. (2003) reported desaturase indices of 0.18 and 0.15 with a grass silage diet without or supplemented with fish oil these values are probably lower than others because the analytical methods accounted for minor CLA isomers that typically co-elute with RA or because of inhibition of A-9-desaturase by the long-chain PUFA from the fish oil supplement. The desaturase index, as defined earlier, should approximate the proportion of VA desaturated in the tissues. A summary of endogenous RA synthesis estimates and the proportion of VA desaturated in the tissues is in Table III. 

A higher intake of concentrate, especially when associated with maize silage, induces a shift in rumen biohydrogenation towards the synthesis of trans- 0, cis- 2 C18 2 and trans-lO C18 1 (Chilliard et al, 2007). Among animal sources, fish oil is more effective than plant oils in enhancing CLA, VA and omega-3 FA in milk fat, especially when fish oil is fed in combination with oil supplements rich in linoleic acid (Figure 1). 

Broderick, G.A, 1992. Relative value of fish meal versus solvent soybean meal for lactating dairy cows fed alfalfa silage as sole forage. J. Dairy Sci. 75, 174-183... 

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