Feed intake in the multiparous lactating sow: its relationship with reactivity during gestation and tryptophan status

Voluntary feed intake in sows after parturition may be related to the capacity of the sow to cope with the numerous changes occurring around farrowing. This experiment was undertaken to investigate whether the feed intake during lactation was related to the reactivity of the sow during gestation and plasma Trp and cortisol concentrations. On d 58 of pregnancy, 37 sows were individually placed in a novel environment, and their behavior was observed during a 5-min open-field test. This test allowed the selection of 12 reactive (R) and 8 nonreactive (NR) sows for the study. Sows were fed 3 kg of a standard gestation diet/d before farrowing and a standard lactation diet ad libitum thereafter. The behavioral reactivity of sows when a human touched their neck in the farrowing crate was evaluated on d 72 of gestation, and their behavior during farrowing was analyzed. Sows were catheterized on d 70 of gestation, and blood samples were taken after an overnight fast on d 37 before farrowing, daily during the week before and the week after parturition, and on d 14 and 21 of lactation for plasma Trp and cortisol determination. The NR sows were less reactive to human contact (P=0.02), had a shorter farrowing duration (P=0.02), and tended to have a shorter birth interval between piglets (P=0.09) than the R sows. Feed intake was greater for the NR sows than for the R sows during wk 1 of lactation (P=0.02), as well as during the whole lactation (P=0.03). Plasma cortisol concentration was maximal on the day after farrowing (P=0.01) and returned to basal concentration within 4 d postpartum. No relationship was observed between sow behavior and plasma concentration of cortisol. For both groups of sows, plasma concentrations of Trp between d 2 and 4 postpartum were less than during gestation (P<0.05). The NR sows had decreased plasma Trp concentrations compared with the R sows during wk 1 of lactation (P=0.02). A low reactivity during gestation was associated with behavior of the sow that was favorable to piglet survival during farrowing, increased feed intake, and decreased plasma Trp concentration during wk 1 of lactation. Further research is needed to elucidate whether Trp or Trp metabolites are related to reactivity and ADFI of the reproducing sow.