Although the use of fish meal is prohibited for ruminants in the European Union and in other countries, it is a valuable source of by-pass protein (cooking fish causes protein binding) and is thus used as a by-pass protein.
In lactating cows, when compared to other sources of undegradable protein such as soybean meal or cottonseed meal, fish meal gave higher results (Broderick, 2005; Broderick et al., 2000; Korhonen et al., 2002), improving amino acid balance and reducing N excretion (Ohgi, 2004; Abu-Ghazaleh et al., 2001; Schroeder et al., 2000).
Cows’ response to fish meal protein is improved by urea treatment in a rice straw-based diet (Talukder et al., 1990; Khan et al., 1990). Fish meal resulted in increases in milk yield and protein yield in dairy cows (Malleson et al., 2008; Ibarra et al., 2006; Broderick, 2004; Ohgi, 2004; Yeo et al., 2003; Korhonen et al., 2002; Hill et al., 1999; Wright et al., 1998), especially if the forage:concentrate ratio is high (Pike et al., 1994). However, several papers referring to low inclusion levels reported that it had no effect on milk yield or milk protein content (Moussavi et al., 2008; Moussavi et al., 2007; Serbester et al., 2005; Allison et al., 2002).
Fish meal also enhanced the response of cows to high milking frequency (Yeo et al., 2003) and reduced PGF2α concentration that could have been responsible for early abortion in lactating cows (Mattos et al., 2002), thus inducing higher conception rates (Staples et al., 1998). Feeding fish meal may also increase milk n-3 fatty-acid content (Abu-Ghazaleh et al., 2001).
In Sheep, the undegradable protein content of fish meal improves forage intake. Inclusion levels range from 2.5% in lambs to 7.5% in milking ewes (FIN, 2000). High protein content improves immune status: feeding ewes with fishmeal during late pregnancy decreased worm infestation and thus reduced the use of anthelmintics (Donaldson et al., 1998).
Fish meal supplementation increases reproduction performance in ewes: conception rates, lamb litter weight, lamb weight and vigour at birth, including colostrum and heat production (Vipond et al., 1996; Robinson et al., 1989; Robinson et al., 1999). Milking ewes supplemented with fish meal produced more milk. Fish meal also improved live-weight gains in early weaned lambs grazing tall fescue (Poppi et al., 1988).