Anouschka Middelkoop

In common pig production systems, piglets are suddenly separated from their mother at 3 to 4 weeks of age, resulting in an abrupt transition from drinking sow’s milk to independent feeding on solid feed. This process is called weaning, and is often accompanied by transport of piglets (to another pen or another company) and mixing with piglets reared by other sows. These abrupt changes in diet, environment and social group, can lead to a lot of stress, which results in poor eating and growing, diarrhoea and the occurrence of stress-related behaviours, such as tail biting. Weaning is therefore often seen as the most stressful event in a pig’s life. Piglets that have already learned to eat solid feed before weaning, eat and grow better after weaning, especially if they have eaten a large amount of this feed before weaning. However, a significant proportion of piglets do not eat before they are weaned or only eat small amounts, despite being offered the feed from a few days after birth onwards. It is therefore important to investigate how piglets can be stimulated to consume solid feed before weaning. Furthermore, the influence of providing solid feed on behaviour and the influence of eating solid feed on gut physiology and gut microbiota are still largely unknown.

This dissertation is divided into two parts. In the first part we investigated the effects of providing solid feed from a young age onwards on the behaviour and the (intestinal) physiology of piglets. In the second part of this dissertation, several strategies were investigated to get more piglets to eat and also to increase the amount they eat before weaning, in order to facilitate adaptation to solid feed after weaning. This was done by giving piglets more opportunities to display foraging behaviour, such as rooting and chewing. Under more natural conditions, piglets already forage from a few days after birth and try out various, partly fibre-rich food resources. In conventional pig farming, however, the possibility to forage is limited, because usually no suitable rooting materials are offered and piglets only receive one type of feed. In this dissertation, foraging in piglets was stimulated by 1) enriching the pen with rooting materials on the floor and extra space, and by alternating chew objects 2) attaching rooting, chewing and playing materials to the feeder to create a ‘play-feeder’, 3) providing diverse feeds in the feeder and 4) hiding feed in the feeder in sand to stimulate food-seeking behaviour.

Providing solid feed from a young age
In Chapter 2 and 3 it was investigated whether early provision of solid feed before weaning (i.e. creep feed, including fermentable fibres) can contribute positively to the behavioural and physiological development of piglets and thus reduce problems after weaning. Piglets given creep feed before weaning grew 12% better in the last week before weaning than piglets who did not receive it, resulting in a trend for a 5% higher weaning weight (Chapter 2). Over the two weeks after weaning, the groups did not differ in feed intake, growth, feed efficiency and diarrhoea, but at the end of these two weeks the piglets that received creep feed before weaning were 6% heavier and 10% more uniform in their body weight. The groups did not differ in a stress marker in the blood and in damaging behaviours associated with stress. We therefore found no indications that providing creep feed before weaning makes the weaning process less stressful. Providing creep feed before weaning had little influence on piglet behaviour, as only the types of exploratory behaviour differed between groups, with piglets given creep feed showing more rooting of the environment but less chewing on faeces or sham chewing than piglets without creep feed. Just before weaning, a subset of piglets was sacrificed to study the digestive system and gut microbiota (Chapter 3).

Piglets that ate the creep feed that they were offered before weaning had a longer (9.6 ± 0.2 vs. 9.0 ± 0.2 metre) and heavier gastrointestinal tract (484 ± 23 vs. 438 ± 14 gram without digesta) than piglets without creep feed. They also had a lower pH in the caecum (6.3 ± 0.05 vs. 6.7 ± 0.06) and colon (6.9 ± 0.08 vs. 7.2 ± 0.08) and a higher concentration of short-chain fatty acids in the colon (69.3 ± 12.4 vs. 41.2 ± 4.3 μmol/gram wet weight). In addition, their colonic microbiome differed before weaning, whereby the microbiota of eating piglets could be associated with fibre-rich feed and the amount of feed they consumed.

Some of the piglets in Chapter 2 received a small amount of the creep feed they received before weaning as familiar feed on top of the feed they received after weaning, which was an unfamiliar feed. We expected that by providing a small amount of familiar creep feed on top of the unfamiliar weaner feed, we would improve feed intake just after weaning and reduce stress. Supplementing the unfamiliar weaner diet with the familiar creep feed stimulated feed exploration up to 3 times, but feed intake was only higher (by 11%) between 9 and 14 days after weaning. Growth and diarrhoea were not affected.

Foraging strategies
In Chapter 4 to 8, the effectiveness of different foraging strategies in the farrowing room was determined with a focus on the transition phase around weaning. This was measured by studying the eating behaviour of piglets before weaning and their adaptability after weaning, reflected in behaviour, skin lesions and damage, faecal consistency and production characteristics.

In Chapter 4, enrichment was added to the farrowing pen by providing rooting materials (straw, sawdust and peat) on the floor and extra space, and by alternating chew objects. Enrichment of the farrowing pen resulted in a higher feed intake before weaning, which was twice as high in the last two days before weaning, compared to barren farrowing pens. Enrichment was continued after weaning and increased feed intake by 10% in the post-weaning period.

In Chapter 5, piglets were given a conventional feeder or the same feeder with rooting, chewing and playing materials attached to it. This created a play-feeder, which allowed piglets to explore and play with it. The play-feeder was indeed visited more often and by more piglets to nose, root, chew and play compared to a conventional feeder. However, the play-feeder did not cause a higher feed intake or more creep feed eaters than the conventional feeder. More ‘good eaters’ (piglets that were scored as an eater on multiple days) were found, however, when the play-feeder was given instead of a conventional feeder to piglets from sows with a low milk production. Although all piglets were fed in a conventional feeder after weaning, the piglets that had a play-feeder before weaning did considerably better after weaning. Over the two weeks after weaning, they ate 15% more and grew 16% more, diarrhoea was 73% less prevalent, 50% less severe (better faecal consistency) and 43% shorter in duration, and piglets had 1.5 times fewer skin lesions. There were also fewer piglets with ear and tail damage in this group.

In Chapter 6, the effect of dietary diversity was tested on the eating behaviour of piglets before weaning. Half of the litters were offered two different feed items at the same time and the other half of the litters one of the feed items, to which a different flavour was added daily (four alternating flavours in total). Litters with two feed items showed more feed-oriented behaviour: they explored the feed 2.6 times as much, had more good eaters, and ate 1.5 times more feed than litters with one feed item with alternating flavours. The positive effect of dietary diversity on early feed intake before weaning was confirmed in Chapter 7, in which the piglets were also monitored after weaning.

In Chapter 7, the piglets were given one feed item or four different feed items simultaneously. Litters with a diverse diet explored the feed 3 to 19 times more, ate 5 times more and contained more piglets that were eating during the suckling period than litters with a monotonous diet consisting of only one feed item. Litters with a diverse diet consisted of twice as many eaters at 11 days of age and all piglets were seen eating before weaning. However, piglets that were given a diverse diet before weaning did not do better after weaning, possibly because dietary diversity was not continued after weaning and they thus suddenly received a monotonous diet. We expected that piglets on a diverse diet would eat more from unfamiliar feed due to the experience with various feed items, but found no indications for this. This was investigated by measuring the feed intake of the unfamiliar weaner diet in the first hours and days after weaning (Chapter 7) and using behavioural tests in which piglets were exposed to unfamiliar food, such as cheese and crisps (Chapter 8).

In Chapter 7, half of the litters were also given the opportunity to display food-seeking behaviour by hiding feed in sand in one feeder of the pen and offering feed without sand in the other feeder of the pen. Piglets explored and ate more often from the feeder with sand than from the feeder without sand. The other half of the litters got two feeders without sand in it. However, litters with the possibility of food-seeking behaviour did not explore and eat the feed more often than litters without the possibility of food-seeking behaviour, but did have more good eaters of creep feed. Piglets that had the possibility of food-seeking behaviour before weaning seemed to have more difficulty to cope with weaning than piglets that did not have these possibilities. This was reflected in 1.4 times more damaging behaviour and 2 times more aggressive behaviour, more lesions on the skin (5.6 ± 0.7 vs. 4.0 ± 0.6 lesions), and a 23% lower feed intake and 44% lower growth, particular in the first two days.

Finally, Chapter 5 demonstrated that the intake of creep feed before weaning is not only stimulated by exploration (Chapter 4 to 7), but is also driven by a low energy intake from milk. In this study, half of the litters were reared by restrictedly-fed sows and the other half were reared by full-fed sows. Piglets of restrictedly-fed sows grew 20% less before weaning and therefore had a 12% lower weaning weight than piglets of full-fed sows, because they received less milk and milk with a lower fat percentage. This caused twice as many piglets to eat before weaning and tended to double feed intake before weaning, and therefore also doubled the feed intake in the first days after weaning. As a result, weaning in this group did not result in a growth dip (128 vs. -32 gram/day in the first two days after weaning) and this group spent less time on ear biting (0.4 ± 0.05 vs. 0.7 ± 0.10% of the time). Two weeks after weaning, piglets from restrictedly- or full-fed sows did no longer differ in their body weight (10.18 ± 0.17 vs. 10.43 ± 0.14 kg). This suggests that litters with a low milk consumption can catch up in growth in the period after weaning by eating more solid feed before and after weaning.

Conclusion
Providing solid feed from a young age in the farrowing room influences the exploratory behaviour of piglets and can improve the growth development of piglets before and after weaning. The adapted gut physiology and gut microbiota of eating piglets before weaning may have played a role in this. In summary, the results from this dissertation support that the provision and intake of solid feed before weaning can accelerate the (intestinal) development of piglets.

The results of this thesis have also led to new feeding strategies that can improve the welfare and productivity of piglets. This was achieved by stimulating the development of natural exploration, play and eating behaviour of piglets from a young age. The foraging strategies in this thesis all encouraged the eating behaviour of suckling piglets, with strategies 1 and 3 being more successful in promoting feed intake behaviour than strategies 2 and 4. However, not all strategies promoted piglet adaptability after weaning. This may be due to the discontinuation of strategies after weaning, except for strategy 1, resulting in loss of enrichment. Nevertheless, the play-feeder before weaning provided a greatly improved adaptability of piglets after weaning. To ensure a good performance of piglets after weaning, a gradual transition to solid feed is important and the housing conditions before and after weaning should be aligned. On the basis of this dissertation, it can be stated that piglets should be given the opportunity to forage and play from a young age onwards, and that this possibility should be retained in the growth phases that follow.