Influence of mild feed restriction and mild reduction in dietary amino acid content on feeding behaviour of group-housed growing pigs

This study investigates changes in the feeding behaviour of pigs as a result of a restriction in their feed allowance and a reduction in dietary indispensable amino acid (AA) content. Ninety-six Topig Talent × PIC barrows were housed in 8 pens and individually fed either ad libitum (AL) or a restricted diet (RF) from 47 to 145 kg body weight (BW). The amount of feed given to RF pigs was close to their expected voluntary intake, but it was limited to proportions of 0.33, 0.66 and 1.00 of the estimated daily amount of feed in 3 time intervals, 00:01 to 8:00, 8:01 to 16:00 and 16:01 to 24:00 h, respectively. From 86 kg BW, the pigs in 4 of the pens were fed diets with conventional standardized ileal digestible AA content (CAA), while the pigs in the other pens received diets (LAA) in which the proportions of dietary indispensable AA were lowered with respect to CAA by 0.91 from 86 to 118 kg BW and by 0.82 from 118 to 145 kg BW. Automated feeders monitored individual feeding behaviour. Data were analysed by pig and feeding phase with a 2 × 2 factorial design. Over the whole experimental period, feed restriction resulted in a decrease in daily feed intake (7%, P < 0.001), the number of visits (27%, P < 0.001) and the time spent feeding (14%, P < 0.001), but an increase in feed consumption per visit (20%, P = 0.001) and feeding rate (10%, P = 0.032). The reduction in AA increased daily feed intake (7%, P = 0.031), tended to increase feeding rate (14%, P = 0.07) and interacted with feeding regime with respect to the number and duration of feeding visits. During growing and finishing, we observed high, negative, non-linear relationships between feed consumption per visit and visit frequency (R2 = 0.989 to 0.876), between visit duration and visit frequency (R2 = 0.648 to 0.695), and between feeding rate and time spent feeding in a day (R2 = 0.802 to 0.707), and positive linear relationships between visit duration and feed consumption per visit (R2 = 0.614 to 0.570). The individual feeding rate during growing was positively correlated with that during finishing (R2 = 0.458). We conclude that pigs try to adapt their feeding pattern to compensate for a reduction in feed allowance or nutrient restriction by, for example, increasing their feeding rate, which may reflect increased feeding motivation.