Nutrient digestibility and nitrogen balance in growing-finishing pigs fed legume-based diets

Four experiments were conducted to determine the effect of replacing soybean meal with pea (two cultivars), faba bean or yellow lupine seeds in pig diets supplemented or not supplemented with feed enzymes on nitrogen balance and nutrient digestibility. The experimental materials comprised 72 hybrid (Polish Large White × Polish Landrace) growing-finishing pigs. Balance and digestibility tests were carried out twice (at the first and second stages of fattening), by the simple balance method. At the first stage of fattening, soybean meal was partially replaced with pea (40% or 46%), faba bean (33%) or yellow lupine (18%) seeds. At the second stage of fattening, soybean meal was completely replaced with legume seeds. Nutrient digestibility from PT-1 diets containing pea seeds of both cultivars was comparable with that noted for standard diets, or even higher. A 33% faba bean content of experimental diets was too high, and it decreased the digestibility of all nutrients. Enzyme supplementation reduced the adverse effect of faba bean, yet nutrient digestibility did not reach the level reported for the control group. A significant increase in nutrient digestibility was noted in pigs fed diets containing yellow lupine seeds, and the beneficial influence of lupine was enhanced by enzyme supplementation. At the second stage of fattening, nutrient digestibility increased when yellow lupine seeds were used as a substitute for soybean meal. The complete replacement of soybean meal with pea and faba seeds in enzyme-supplemented diets also positively affected nutrient digestibility. Soybean meal substitutes had no negative impact on nitrogen balance at both stages of fattening. A two-factorial analysis of variance (with legume species and dietary enzyme supplementation as experimental factors) showed that pea and yellow lupine seeds are suitable substitutes for soybean meal in pig diets.