Response of the Iberian sow to protein supply and feeding level during late gestation

One hundred and twenty purebred Iberian (IB) sows in their second or third parity were used in two consecutive trials to determine the effects of dietary crude protein (CP) concentration and feeding level (FL) during late gestation on sow and litter performance. The sows were kept in groups in open-air, fenced spaces and randomly assigned from day (d) 70 of gestation to one of four experimental treatments in a 2 × 2 factorial arrangement with 2 CP levels (120 and 101 g CP/kg diet) and 2 FL (2.33 and 2.67 kg/d; metabolizable energy (ME) content, 12.50 MJ/kg diet). Nearing farrowing the sows were housed individually and fed a lactation diet (148 g CP/kg; 4.5 kg/d) for a 35-d lactation period. Piglets had no access to any feed. Body weight (BW) gain from d 70 of gestation to farrowing increased with FL (23.8 ± 0.88 vs. 27.3 ± 0.86 kg; P < 0.01, in second-parity sows; 18.2 ± 1.14 vs. 25.0 ± 1.23; P < 0.001, in third-parity sows), but was not affected by dietary CP content. Average BW gains were 25.6 ± 0.59 and 21.6 ± 0.83 kg in second- and third-parity sows, respectively. Body weight loss during lactation was not affected by FL, and in second-parity sows it tended to increase with the lowest CP diet (P = 0.071). The CP × FL interactions were never significant (P > 0.05). The dietary factors did not affect plasma metabolite levels in late gestation, except plasmatic urea which decreased in third-parity sows with FL. In lactation, plasma urea level increased with CP (P < 0.05) in second-parity sows, and on increasing FL (P < 0.05), in third-parity sows (P < 0.05). The proportion of pigs born alive was not affected by the sows’ nutritional treatment. In second-parity sows, treatment did not affect total litter weight at birth or at weaning. On the contrary, in third-parity sows, total litter weight at birth increased on increasing dietary CP content (P < 0.05). Also, total litter weight at weaning tended to increase in third-parity sows fed the highest FL (P = 0.073). Pig BW at weaning was 8.09 ± 0.110 and 8.05 ± 0.135 kg, respectively in the second- and third-parity sows. In conclusion, a daily provision of at least 2.67 kg of the diet containing 120 g CP/kg to the IB sow during the last third of pregnancy ensures adequate nutrient supply to fetuses and body reserves for lactation. This feeding regime provides 33.4 MJ ME and 247 g apparent digestible protein.