In poultry, linseeds are of a lesser nutritional value compared to other oilseeds, due to their physical structure, their deficiency in lysine, and the presence of antinutritional factors, such as anti-pyridoxine and mucins. These cause high viscosity of digesta and result in lower performance and feed efficiency (Shen YingRan et al., 2004; Pekel et al., 2009; Alzueta et al., 2003). However, their high content in omega-3 fatty acids has led to their increasing use in poultry. Many experiments have investigated processing methods for improving the nutritional value of linseeds in poultry and have tried to determine their optimal inclusion rates (Shen YingRan et al., 2005b; Van Elswyk, 1997).
The recommended inclusion rates of linseeds for broilers range between 2 and 10% of the diet (Ochrimenko et al., 1998; Richter et al., 1998; Bakhiet et al., 1995; Kang et al., 1994). However, it has been suggested that including linseeds at up to 12%-15% in the diets of broilers could improve the omega-3 fatty acid content of the meat without impairing performance too much (Huthail Najib et al., 2011; Pekel et al., 2009; Shen YingRan et al., 2005a). Pelleted or roasted linseeds should be used in preference to raw linseeds. Linseeds have a lower energy value than other oilseeds, with TME values for raw seeds about 14-15 MJ/kg DM, and a low fat digestibility (61%) (Shen YingRan et al., 2004; Lee et al., 1995). The low energy value can be increased by processing. Pelleting and autoclaving were found to increase the TME up to 17-18 MJ/kg DM (Shen YingRan et al., 2004). Pelleting and roasting increased the digestibility of total fatty acids by 29% and 39%, respectively (Shen YingRan et al., 2005b). Pelleted linseeds at an inclusion rate up to 10% of DM did not impair performance (Shen YingRan et al., 2003). In Saudi Arabia, roasting linseeds and including them at 15% in broiler diets had a positive effect on omega-3 fatty acid content and animal performance (Huthail Najib et al., 2011).
The addition of vitamin B6 to counterbalance the effect of linatine enhanced animal performance (Shen YingRan et al., 2003). The addition of antioxidants to poultry diets containing 15% linseeds resulted in increased levels of polyunsaturated fatty acids, in a lower content of saturated fatty acids and in a lower omega-6:omega-3 ratio (Ajuyah et al., 1993). Fibre-degrading enzymes (carbohydratase) and the progressive introduction of poultry to linseeds have been shown to alleviate the antinutritional effects of mucins (Slominski et al., 2006).
Feeding linseeds in mixture with other seeds had a positive effect on both animal performance and omega-3 deposition. A diet containing an extruded or non-extruded combination of linseeds with peas or rapeseeds, included at 12.5% of the diet, as a partial replacement for soybean meal, resulted in similar growth rate and feed conversion efficiency (Thacker et al., 2005). A diet supplemented with a mixture of 6% linseeds and 6% rapeseeds resulted in better animal performance than diets supplemented with 8% of either seeds alone (Krasicka et al., 2000).
Feeding linseeds for longer than 16 days may result in a pH drop and subsequent poor meat quality (cooking losses, drip loss, and higher susceptibility to oxidation) (Betti et al., 2009b). However, it was shown that an omega-3 fatty acid content of 300 mg/100 g meat in breast, thigh and wing meat required at least 26 days at 10% inclusion rate or at least 11 days at 17% inclusion (Betti et al., 2009a). Other experiments report longer feeding periods (36 days at 12% in Canada, 42 days at 15% in Romania) (Jia et al., 2011;Taulescu et al., 2011). It is likely that optimal inclusion rates are a trade-off between health requirements and meat quality.
Including linseeds in layer diets is done worldwide, including in warm climates, in order to increase the omega-3 fatty acid content of eggs and decrease their omega-6:omega-3 ratio (Ahmad et al., 2013; Al-Nasser et al., 2011).
Linseeds could increase the omega-3 content in eggs and reduce the omega-6:omega-3 ratio at levels starting from 5% (Criste et al., 2009). Inclusion rates reported in experiments range from 7.5% to values as high as 20% (Ahmad et al., 2013; Gurbuz et al., 2012; Al-Nasser et al., 2011; Betancourt et al., 2009; Leeson et al., 2007; Bean et al., 2003; Basmacioglu et al., 2003; Sari et al., 2002; Botsoglou et al., 1998; Roth-Maier et al., 1998; Aymond et al., 1995; Cherian et al., 1991; Caston et al., 1990). However, inclusion rates over 10% can hamper performance (hen weight; laying performance, egg mass, yolk weight, yolk percentage, feed costs) (Ahmad et al., 2013; Betancourt et al., 2009; Bean et al., 2003; Sari et al., 2002; Novak et al., 2001; Roth-Maier et al., 1998). Some authors recommend including linseeds at levels below 10%. For example, linseeds included at 7.5 %, 8.6% or 10% had no negative effect on performance (egg weight, yolk weight, yolk ratio, albumen weight, albumen ratio, shell weight, shell ratio, shell strength and shell thickness) but still resulted in omega-3 accumulation in egg yolk (Al-Nasser et al., 2011; Basmacioglu et al., 2003).
Processing and supplementation have been proposed to alleviate the negative effects of linseeds on layer performance. Roasted linseeds included at 10% resulted in higher production than raw linseeds (Huthail Najib et al., 2010). Grinding linseeds had a positive effect on egg weight (Yannakopoulos et al., 1999). Ground linseeds at 15% or at 16% of DM supplemented with vitamin B6 had a positive effect on omega-3 fatty acids in yolk and no deleterious effect on its susceptibility to rancidity (Aymond et al., 1995; Cherian et al., 1991). A diet based on pearl millet (Pennisetum glaucum) as main source of grain, in combination with linseeds (at 4, 6 or 8%) and natural pigments (at 0.1%), allowed to reduce linseed inclusion down to 6% while yielding as much omega-3 fatty acids as needed to meet the standard for "omega-3 enriched" market eggs, without hindering performance (Amini et al., 2008).
Linseeds included at 9% and above in layer diets reduced cholesterol in egg yolk (Basmacioglu et al., 2003; Sari et al., 2002). However, such a reduction was not observed in an earlier experiment (Botsoglou et al., 1998).
Trained panelists have been able to identify eggs from hens fed linseeds by noting differences in flavour, aroma and off-flavour (Hayat et al., 2010). In a 1992 study, 36% of sensory evaluations reported fishy or fish-related flavour in eggs from hens fed linseed, which was absent in eggs from hens fed no linseeds or fed high-oleic acid or high-linoleic acid sunflower seeds (Jiang et al., 1992). However, in a later study, eggs from hens fed a linseed diet enriched with thyme had the highest scores for odour, flavour, and overall acceptability, as well as the lowest score for off-flavour (Tserveni-Goussi, 2001).