Effect of productive variety and dietary protein on digestive efficiency and fractional synthesis rate

This assay aims to analyse the influence of the genotype/productive variety and dietary crude protein (CP), on digestive capability and protein deposition in growing pigs, in order to improve further precision feeding and productive efficiency. For this purpose, 16 growing pigs of two different varieties were used: entire hybrids (F2) progeny of [F1: Duroc × Landrace] ♀ × Pietrain ♂, and castrated purebred Durocs (D) (30.5 ± 1.27 and 25.19 ± 0.91 Kg of BW, respectively). Half of the pigs of each genotype were fed with diets which differed on CP content (LP 15% vs. NP 17%). Performance and digestive efficiency parameters were determined;protein fractional synthesis rate (FSR) was analysed using the flooding dose technique, which consisted of an intravenous infusion of phenylalanine (containing 15% of (2H5-Phe)) with subsequent blood sampling from 12 to 40 min after the start of the infusion and sacrifice of the animals. Fat incorporation rates (IR) were analysed comparing the concentration of deuterated stearic acid (added to the diet during the experimental period) in tissues and plasma. F2 pigs showed a higher feed intake (P<0.05) compared to Duroc, although their growth didn't differ (P>0.05). The protein content didn't influence the feed intake, except in the intake of crude protein (CP). Average daily gain was higher in animals fed LP diet compared with NP (P <0.05); this effect was especially noticeable in the F2 variety, whose growth (kg/day) was (0.33 ± 0.08 NP vs. 0.53 ± 0.08 LP), with respect to Duroc (0.38 ± 0.04 NP vs. 0.36 ± 0.05 LP). Apparent dry matter (DM) digestibility was higher in Duroc pigs, and in pigs fed NP diet (P<0.05); pigs fed NP diet also showed a higher real CP digestibility. The FSR was not affected either by the productive variety or by the level of CP in the diet. Fat IR was affected by the animal genetics, presenting Duroc animals higher rates of fat incorporation in liver and muscle (P<0.05). No differences were found between both varieties in subcutaneous tissue, probably due to the high individual variability in fat deposition observed in young pigs.