Effect of increasing amounts of straw on pigs’ explorative behaviour

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According to European legislation, pigs must have permanent access to sufficient quantity of materialto enable manipulation activities. However, few studies have quantified how much straw is needed tofulfil the requirements of growing pigs. We investigated the effect of increasing amount of straw on pigs’manipulation of the straw, and hypothesised that after a certain point increasing straw amount will nolonger increase oral manipulation further. From 30 to 80 kg live weight, pigs were housed in 90 groups of18 pigs in pens (5.48 m × 2.48 m) with partly slatted concrete floor and daily provided with fresh uncutstraw onto the solid part of the floor. Experimental treatments were 10, 80, 150, 220, 290, 360, 430 or500 g straw per pig and day. At 40 and 80 kg live weight, the time spent in oral manipulation of the strawby three focal pigs per pen (large, medium and small sized) were recorded along with the percentage ofpigs manipulating straw simultaneously. This was recorded in three 1-h intervals (1 h before and 1 h afterstraw allocation in the morning, as well as from 17 to 18 h in the afternoon). With increasing quantity ofstraw provided, we found a curvilinear (P < 0.01) increase in the time spent in oral manipulation of thestraw. Smaller pigs spent more time manipulating straw than larger and medium sized pigs (367, 274and 252 s/h for small, medium and large sized pigs, respectively; P < 0.001), and pigs spent more timemanipulating straw at 40 kg than 80 kg live weight (356 vs. 250 s/h; P < 0.001). At both live weights, pigsspent most time manipulating straw during the hour after allocation of straw. Similar effects of increasingamounts of straw were found for the percentage of pigs engaged in simultaneous manipulation of thestraw. Post hoc analyses were applied to estimate the point, after which additional straw did not increasemanipulation of straw any further. For the time spent manipulating straw the estimated change pointwas 253 (approx. 95% confidence limits (CL) 148–358) g straw per pig and day. For the number of pigssimultaneously manipulating straw the change point was 248 (CL 191–304) g straw per pig and day. Theseresults show that increasing the quantity of straw from minimal to approximately 250 g per pig and dayincreased the time spent in oral manipulation of the straw, as well as the occurrence of simultaneousstraw manipulation.Hence, data from the current experiment identified 250 g straw per pig per day as the amount ofstraw where a further increase in straw provision did not further increase neither time spent on oralmanipulation of straw, nor the percentage of pigs simultaneously manipulating straw. This suggests that,within the current housing system and using this criterion, this amount of straw may be the biologicalturning point for increasing oral manipulation of straw.
Original languageEnglish
JournalApplied Animal Behaviour Science
Pages (from-to)58-63
Publication statusPublished - 2015

    Research areas

  • Exploratory behaviour, straw, rooting material, growing pigs, welfare

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