Rye grain and rye by-products may contain several toxic antinutritional factors (see Potential constraints), which reduce rye palatability and nutritional value for pigs (Korobov et al., 2005). Ergot, particularly, has deleterious effects on pig health and performance (Blair, 2007). Only ergot-free rye grain and rye by-products should be fed to pigs (Sullivan et al., 2005).
The digestible, metabolizable and net energy values of rye grain are slightly lower than those of wheat and maize but higher than those of barley and oats. The energy digestibility in growing pigs is higher (84%) than that of barley (81%) (Sauvant et al., 2004). Digestibility of the amino acids in rye grain are lower (5-10%) than in wheat and barley (Blair, 2007).
Rye grain should not be fed to weanling animals as it may cause digestive disorders. In growing-finishing pigs it has been recommended that rye grain replace no more than 50% of maize in the diet (Sullivan et al., 2005). The growth of pigs on diets with 50% rye was 11-12% slower than on diets formulated with 50% barley (Maner, 1987). In an experiment where pelleted or unpelleted rye grain was fed at 30 and 60% of the diet, animal performance decreased with the unpelleted rye grain, but with pelleted rye grain, performance was equal to that from barley (Friend et al., 1969). More recent results have found no differences between growing pigs fed 53% of either rye or barley (same level) (ICSR, 2013). A mixture of wheat, rye and barley (25:25:25) was used as a basal diet for growing pigs. It compared favourably with a maize-based diet, giving a higher feed intake, improved feed:gain ratio and better animal performance (Willamil et al., 2012). Growing pigs fed on a rye-based diet at higher levels of rye (above 80%) had similar growth rates and feed intake to pigs fed barley and tended to have a better feed conversion (Thacker et al., 2002).
Fattening pigs and sows
In finishing pigs, digestibility coefficients for dry matter, crude protein and gross energy were significantly higher for the rye-based diets than the barley-based diet. Finishing pigs fed rye-based (80% rye) diets (containing either low or normal viscosity rye, supplemented or not with enzymes) gained significantly faster, with a better feed conversion than pigs fed barley. Males gained faster and had higher feed intakes than females. Pigs fed normal rye had a similar daily intake and gain to pigs fed barley-based diets. It was shown that low viscosity rye or enzyme supplemented rye had no beneficial effect on pig performance and carcass traits (Thacker et al., 2002).
Because of the deleterious effect of ergotism on reproductive performance (abortion, agalactia and loss of piglets at farrowing), only ergot-free rye grain should be fed to sows (Sullivan et al., 2005; Maner, 1987). Recommendations for rye grain inclusion in sow diets depend on the type of production. Rye grain inclusion can reach 10% in commercial sows (Ewing, 1997). Conventional nursing sows should not be fed on rye grain (Sullivan et al., 2005). A level of 40-50% dietary inclusion was suggested for organically farmed sows (either lactating or gestating) (Blair, 2007).
Rye bran contains high levels of phytase that enhances phytic P availability in pigs. Feeding growing pigs on a phytase-rich diet (20% rye bran) had a positive effect on phytate P availability and thus increased P absorption (55 vs. 36%) and retention (50 vs. 36%). Rye bran also enhanced Ca retention and pigs showed greater bone density, ash content, and bending moments (Pointillard, 1991).