Effect of two different feeding strategies on energy intake from pasture, feed efficiency and growth performance of growing-finishing pigs in a mobile pasture system

Free-range rearing allows pigs to perform species-specific and normal behavior, and is an important welfare attraction among consumers, but high inputs of concentrate challenge the sustainability of this practice. Exposing pigs to limited access to concentrate followed by ad libitum feeding could reduce feed input while improving average daily gain and feed conversion ratio. The objective of the study was to investigate the effects of restricted feeding in the grower phase followed by ad libitum feeding in the finisher phase on growth performance, feed efficiency and intakes from concentrate and the range area in a rotational pasture system. A total of 64 pigs with a mean live weight (LW) of 30 kg (SD 3.9) and an average age of 69 days were randomly assigned to one of two feeding strategies; AL (ad libitum from 30 kg LW to slaughter) or RES-AL (restricted feeding supplying 95-67% of recommended supply from 30 kg to 70 kg followed by ad libitum feeding until slaughter). Slaughter of RES-AL pigs was performed after 84 days, while AL pigs were slaughtered after 76 days. Access to new pasture area was provided twice a week throughout the experiment using mobile paddocks. Results showed that RES-AL pigs partially achieved compensatory growth as their growth rate was numerically greater (71 g/d) than for AL pigs during realimentation from 70 kg to slaughter (1419 vs. 1348 g/d). Daily growth rates from 30 kg to slaughter were high across feeding strategies, 1051 g vs. 1139 g for RES-AL and AL, respectively (P < .001). Concentrate feed conversion efficiencies were also high, 34.2 MJ ME/kg LW gain for RES-AL pigs and 34.5 MJ ME/kg LW gain for AL pigs (P > 0.05). It was estimated that RES-AL pigs covered 25% of daily energy requirements from direct foraging during restricted period and 10% during realimentation. For comparison on the corresponding periods, AL pigs covered 14% and 6%, respectively. Findings indicate a great potential for high growth rates and high feed efficiencies under free-range conditions as well as substantial energy inputs from direct foraging, most pronounced during concentrate restriction. Due to the lack of improved feed efficiency for RES-AL pigs compared with AL pigs, the sustainability was not improved in free-range reared pigs when focusing on concentrate input exclusively.

Automated summary

The study investigated the effects of restricted feeding in the grower phase followed by ad libitum feeding in the finisher phase on growth performance, feed efficiency, and intakes from concentrate and the range area. Results showed that partially compensatory growth was achieved by pigs under the restricted feeding regime, with high growth rates and feed efficiencies observed in both feeding strategies under free-range conditions. However, energy inputs from direct foraging were more pronounced during concentrate restriction, indicating potential sustainability challenges for free-range reared pigs.