The daily feeding behaviour of growing pigs subjected to a feed restriction and to a reduction of dietary indispensable amino acid contents

his experiment aimed to evaluate the changes in the eating behaviour caused by a restriction of feed allowance and a reduction of the dietary indispensable amino acid content. Ninety-six Topig TalentPIC barrows, allocated in 8 pens (12 pigs/pen), were individually fed according to an ad libi- tum (AL) or a restricted (R) feeding regime, from 47 to 145 kg body weight (BW). The feeders, one per pen, recorded the visits to the feeder, the time spent eating and the feed intake (FI) in each visit. The R pigs received amounts of feed close to their expected voluntary intake during 3 time intervals, 00:00 to 8:00, 8:01 to 16:00 and 16:01 to 23:59h, when they were allowed to eat 33, 66 and 100% of the amount of feed planned for that day, respectively. The pigs of 4 pens received feeds with conventional standardized ileal digestible amino acids content (CAA), according to NRC (2012). The other pigs received feeds (LAA) that, in early (86-118 kg BW) and late finishing (118-145 kg BW), contained indispensable amino acid contents lowered by 0.09 and 0.18 with respect to the CAA feeds. Data, averaged by pig, were analysed as a 2 2 factorial design, with the following 4 lev- els: AL-CAA, AL-LAA, R-CAA, and R-LAA. The eating activity of pigs was largely diurnal. As overall mean, the pigs of this experiment consumed 2619 g/d in 57.7 min/d and made 8.8 eating visits, with a feeding rate of 47g feed/min (Supplementary Table 1). Feed restriction (R vs AL) reduced the daily FI (7%, p<.001) and the number of visits (27%, p<.001), but increased FI per visit (20%, p 1⁄4 .001) and the eating rate (10%, p 1⁄4 .032). The dietary amino acid reduction applied in late finishing (LAA vs CAA) increased the daily FI (10.5%, p1⁄4.037), tended to increase the eating rate (19.6%, p1⁄4.06) with both feeding regimes, and tended to interact (p<.10) with the feeding regime for other eating traits. In fact, under AL conditions, dietary amino acid reduction increased the daily FI and the visit frequency, but reduced the FI per visit, where the oppos- ite occurred under R conditions. The coefficient of variation of all the behaviour traits (rang- ing 0.18 to 0.66) was always larger than that found for the daily FI (0.10). Strong relationships between FI per visit and the visit frequency (R2 1⁄4 0.93), and between the eating rate and the time spent eating (R2 1⁄4 0.80) were found. The behavioural flexibility of the pig in the attempt to achieve their desired feed intake was evidenced. Acknowledgements The research was funded by the University of Padua under grant number CPDR143385/14 and DOR1655405/16. The authors would like to thank Veronesi SPA (Quinto di Valpantena, Verona, Italy) for financial and technical support, and Aldo Gini Foundation (Via Portello, 15, Padova, Italy) for supporting the research activities of Msc Giuseppe Carco, during his stage at the University of Zaragoza.