Porcine digestible peptides as alternative protein source in weaner diets: effects on performance and systemic cytokine profile in pigs followed from weaning to slaughter

Porcine digestible peptides (PDP) are high-quality hydrolysed proteins obtained from porcine intestinal mucosa as a by-product of the heparin manufacturing process. PDP contain bioactive peptides and are used as alternative protein sources in several animal species, including pigs. We aimed to explore the (carry-over) effects of feeding PDP to weaned piglets on performance and systemic cytokine levels of pigs followed until slaughter. A total of 192 piglets were allocated to one of two dietary treatments: control (CON) or PDP weaner diets. PDP was included at 5.0% until day 13 post-weaning at the expense of skimmed milk powder and partial replacement of soybean meal, and at 2.5% between days 13 and 34 post-weaning at the expense of soy protein concentrate. Grower-finishers were fed commercial diets according to a 3-phase feeding scheme until slaughter, when carcass traits were determined. Six pigs were housed per weaner pen and eight per grower-finisher pen with 16 and 10 pens per treatment, respectively. Pigs were weighed at the start and at the end of each phase, and feed intake was recorded. Faecal consistency was recorded twice a week in the weaner facility. Ten pigs per treatment were sampled for blood at days 13, 34 and 69 post-weaning. We found that PDP-fed piglets had a higher feed intake in the first two weeks post-weaning compared to CON-fed piglets (+32 g/pig per day; P = 0.02). Moreover, piglets in the PDP group showed improved feed conversion between days 13 and 34 versus the CON group (1.36 vs 1.43; P = 0.03). Piglets that were fed with PDP in the weaner diets tended to grow faster in the grower-finisher period (+32 g/pig per day; P = 0.07), tended to reach slaughter age earlier (129.9 vs 131.5 days; P = 0.07) and had a lower dressing percentage at slaughter (76.3 vs 76.7%, P = 0.045) than piglets previously fed with CON. Additionally, PDP-fed piglets showed higher serum levels of pro-inflammatory cytokines interleukin (IL)-12 (P = 0.02), tumour necrosis factor-alpha (P = 0.02), interferon-gamma (P = 0.03) and IL-8 (at day 34 post-weaning, P = 0.06) as well as anti-inflammatory cytokines transforming growth factor-beta (P = 0.02), IL-4 (P = 0.04) and IL-10 (at day 34 post-weaning, P = 0.02). No significant differences among dietary treatments were observed regarding faecal consistency of weaned piglets and carcass weight, lean meat percentage, muscle depth, and back fat thickness at slaughter. We conclude that feeding PDP, as an alternative to conventional milk and soy protein sources, showed positive effects on pig performance, not only during the provisioning period but also thereafter into the grower-finisher phase.