Supplementation of female piglets from 1 to 28 days of age with a synbiotic: what consequences on cognitive abilities?
Résumé
The influence of feed supplements on behavior and memory has been recently studied in livestock species. However, none of the studies in pigs have investigated supplement effects in the same individuals during different cognitive tests. The objectives of the study were to evaluate the effects of a synbiotic on an episodic-like (Object recognition: OR), a working (Barrier solving: BS) and a long-term (T-maze) memory test. A total of 18 female piglets were supplemented from 1 to 28 days of age with a synbiotic (SYN) containing strains of
Lactobacillus, fructo-oligosaccharide and beta-glucan included in chocolate milk, whereas a further 17 only received the chocolate milk (CTL). At weaning (means ± SD; age 18.1±1.8 days, weight 13.8±2.4 kg), they were grouped by 8. A period of habituation in the test arena of 3 successive days (2 trials per day of 5 or 10 min) for the piglets to isolation preceded the OR and BS tests. In farrowing crates, they were exposed for 24 h to an object to chew before the OR test to acclimation to objects. The OR test at 16 days of age tested the ability to remember an object already explored 50 min before. The BS test at 20 days consisted of finding a route through two barriers to join two companion piglets, over five successive trials. The T-maze test between 33 and 41 days consisted of finding a food reward. The test was preceded by another 4 days period of habituation to isolation and learning of the food reward. A total of 9 piglets with no interest for the reward were removed from that test. The test was divided into 2 periods: 6 days of acquisition using the same arm rewarded and 3 days of a reversal stage. The treatment effects were evaluated using ANOVA, with repeated measures for the BS test. Treatment groups had no effect on traits of habituation periods (P>0.1). In the OR test, both treatment groups explored the reference objects and environment the same way (distance travelled, frequency and duration of interaction, P>0.1). SYN piglets interacted quicker with the novel object than
the CTL piglets (165±116 vs 255±120 s; P<0.05). In the BS test, no differences were found regarding the times needed to cross each barrier and to finish the test (P>0.1). Performances in trial 1 were lowest for all traits (P<0.001), confirming that piglets used their short-term memory. SYN piglets had shorter distances to finish the test in trial 3 (4.2±1.0 vs 7.4±5.2 m; P<0.05). In the T-maze test, number of correct choices and time to succeed were similar (P>0.1), except on day 3 of the acquisition stage where SYN piglets were quicker than CTL piglets (13.0±6.2 vs 25.8±18.3 s; P<0.05). During the reversal stage, SYN piglets tried the new rewarded arm earlier than CTL piglets (10.3±10.9 vs 19.8±15.4 trials; P<0.05). The synbiotic supplement may confer memory advantages in the 3 cognitive tasks, regardless of the nature of the reward and the memory request. However, differences in motivation to solve the tasks cannot be completely excluded.