Growth, body composition and nutrient balance of pigs fed low protein diets with minimal soybean meal

Surplus of nitrogen (N) in agricultural system and dependance on imported protein feed challenge the sustainability of the Swiss pig production. We aimed at feeding 48 pigs from 22 to 105 kg body weight (BW) grower and finisher diets with minimal imported protein source, soybean meal in particular, and simultaneously reducing dietary crude protein (CP) content compared to actual two-phase feeding practice. The pigs were blocked by litter, gender and BW. Each pig of a block was assigned to either a control (C) or a low protein (N-) grower (25-60 kg BW) and finisher (60-100 kg BW) diets, both being iso-energetic. In N-, soybean meal was replaced by local protein pea, rapeseed expeller and eight synthetic amino acids (AAs) to reach minimal CP, but equal digestible AA contents as in C. Compared to C, grower and finisher N- diets contained respectively 2.7% and 0% soybean meal and 140 and 115 g CP/kg, leading to 10% and 15% less CP content. Their costs increased, however, by 5 and 3%, respectively. Daily individual feed intake and BW at start (T0), diet change (T1, 60 kg BW) and end (T2, 100 kg BW) were recorded. Blood samples were collected at T1 and T2. Fecal and urine spot samples were collected between T0 and T1 as well as T1 and T2. Nutrient excretion was derived by subtracting body nutrient accretion measured by dual X-ray absorptiometry at T0, T1 and T2 from total nutrient intake. Neither apparent total tract digestibility of N, nor growth performance, nor pig’s body composition (lean and fat tissue mass) was affected by diets (P ≥ 0.10). Compared to C, the pigs fed N- had lower (P < 0.01) levels of blood (-30.6% and -21.8%) and urinary urea (-27.1% and -33.7%) and decreased (P < 0.10) fecal N concentration on a DM basis (-4.4% and -9.7%) during growing and finishing periods, respectively. The intake and excretion of N was reduced (P < 0.01) in grower, finisher and overall periods in N- pigs. These findings illustrate that it is technically feasible to replace imported protein sources with local ones. With an appropriate supplementation of the eight limiting AAs, the inclusion of protein rich feedstuffs could be minimized, thus resulting in very low CP contents to successfully reduce N excretion without compromising pig’s growth of lean and fat tissue. The challenge of success in such feeding strategies consists in the market availability of sufficient local protein sources and in the increased feed costs, mainly attributed to four AAs being valine, leucine, iso-leucine and histidine.