Pigs feeding in Intensive and Extensive Production Systems
In modern husbandry systems, gestating (pregnant) sows are typically fed a restricted food allowance just above their maintenance requirements allocated in one or two daily concentrate meals. The level of feed provided is well below the voluntary intake of the animal and is associated with negative animal welfare aspects in the form of prolonged hunger. The restricted feeding of parent stock is described in more detail in Chap.
Allowing these animals to meet their energy requirements, by feeding more energy-rich diets, may simply change the nature of the problem, as the associated increase in live weight can have severe negative effects on both health and production. Another option is to make the diet more bulky to increase gut-fill and prolong (or induce) the feeling of satiety. A number of investigations of the effects of increased dietary fibre on animal welfare have been carried out in gestating sows. The general consensus is that although inclusion of high levels of dietary fibre to restrictedly fed sows may have satiating properties, it provides only transient reductions in feeding motivation, i.e. the animals are still feeling hungry. However, depending on the types of fibre used, bulky feed can reduce aggression and the incidence of stereotypes.
The welfare of restrictively fed animals may be improved, at least in theory, if they spend more time obtaining their food. It may be possible to exploit the natural motivation of pigs to explore and engage in appetitive foraging, especially if the behaviour is occasionally rewarded by the discovery of edible morsels. One way of obtaining this is to provide the daily amount of feed in smaller, more frequent meals. Feeding the ration in two daily portions may increase night time satiety in gestating sows. Another way of supplementing a quantitatively unsatisfying diet is to give these non-ruminant animals access to roughage. This can be in the form of litter or supplied from feeders or racks. Access to straw, although of limited value for satiety, allows the animals to engage in species-specific foraging.
The feeding of gestating sows is a good example to illustrate how the necessity for restricted feeding impinges on other aspects of the sow environment, which in turn affect their welfare. Until recently, many sows in modern production systems were kept in individual stalls with little possibility for movement in order to ensure that each sow got its allocated ration. The development of automatic feeding systems, such as the electronic sow feeder, allows controlled feeding of gestating sows kept in groups, as only one sow at a time can enter the feeder. However, because the sows are hungry, their attention is often centred on the entrance to the feeder, which can result in aggression and vulva biting of the sow occupying the feeder. On the positive side, data from electronic sow feeders can be used to detect health problems, such as lameness, when the feeding pattern of individual sows changes from that usually observed.
One attempt to reduce sow competition for access to an electronic feeder has been to equip it with a loudspeaker programmed to play an individual sound immediately before each sow receives a portion of feed. In this study, animals were called six times daily to be fed the respective fraction of the daily feed allowance. On average, the animals entered the feeder following 80 % of their calls after 8 days of conditioning. At the start of the training, dominant sows blocked the entrance of the feeder, but this behaviour decreased significantly as these sows learned to recognize their own signal for entering the feeder. Subsequent work has shown that sows are able to remember their individual sounds in the following gestation period.
Lactating Sows and Their Piglets
In feral pigs, the weaning process is gradual, with suckling ceasing when the piglets are around 17 weeks of age. Piglets in most commercial production systems are weaned abruptly and at an early age (3–4 weeks). The young piglet is separated from the sow, and the regular intake of warm milk from a teat is suddenly replaced by a trough with solid food and cold water available from a nipple- or cup-drinker. This leads to a delay in feeding post-weaning and a high incidence of diarrhea. One way of ameliorating the transition between feeds at weaning is to allow piglets access to post-weaning feed whilst still with the sow, so-called creep feeding. Creep feeding initiated 5–10 days from birth has been found to reduce significantly the post-weaning diarrhea scores in piglets.
In a series of experiments, a Dutch research group investigated whether piglets were able to learn aspects of eating solid feed from their mother and whether this would benefit the welfare of the piglets after weaning. They found that the presence of the mother during encounters with novel food decreased food neophobia in piglets, as they approached the novel food sooner, more piglets sampled it, and more of the novel food was eaten. Piglets were also found to eat more of solid food before weaning if they could observe or participate when their mother was eating the same food, and they would eat more from a trough position previously used by the dam. Finally, when sows were fed a flavored food during late gestation, piglets were found to eat more, weigh more, and have a lower occurrence of diarrhea post-weaning when given access to similarly flavoured food that they had been exposed to prenatally.
These experiments demonstrate the importance of the sow in the vertical transfer of information about feed to her offspring and that this may be exploited in commercial settings to reduce the post-weaning stress experienced by piglets.
Growing and fattening pigs are most often fed ad libitum, and the concentrated form of the feed means that ingestion of the daily amount is very rapid. In nature, pigs will spend a considerable amount of time searching for food, and when this is no longer required, pigs may redirect their appetitive foraging towards their pen-mates in the form of rooting, chewing, or biting the ears, tails, and bellies of conspecifics. This may be at least partially prevented by supplying small amounts of food, which are not readily accessible, but which can be acquired through rooting, biting, or other manipulation. Provision of such rooting materials to growing pigs has been obligatory in the European Union (EU) since 2003 through legislation.
Access to straw has a number of beneficial effects for the general welfare of pigs, as it allows natural rooting behaviour to occur, reduces chewing of pen-mates, and the incidence of tail biting. found more activity when straw was provided and, as a consequence, a higher frequency of aggressive encounters, but also a higher growth rate.
Cost of purchasing, manure handling constraints, and concern for hygiene and biosecurity are the main reasons that otherwise suitable roughage materials are not used more widely in production systems for growing pigs and gestating sows. Therefore, other measures, such as objects or devices, are often employed, although many of them, such as chains and rope, do not resemble the description found in the EU legislation above. For any enrichment measure, there is a risk of habituation when the animal becomes accustomed to the device resulting in declined usage over time. In a study of environmental enrichment, van de Weerd et al. (2003) examined no less than 74 different objects to assess their potential enrichment value for pigs of different ages. They found that objects with high initial attractiveness were characterized by being odorous, deformable, and chewable, whereas sustained interest was maintained for objects, which were ingestible and destructible.
From a feeding point of view, it is interesting that two of the most intensively and persistently used enrichment objects were lavender straw with whole peanuts and coconut halves suspended on a string.
The accessibility of the feed will affect the feeding behaviour of an animal, and this is important to consider for growing pigs kept in groups, as this impinges on aspects such as the maximum animal to trough ratio. If it is difficult for growing pigs to gain access to the feed (e.g. when a door is placed in front of the trough to protect the feeding animal) this will result in fewer, but longer meals, most often without affecting the level of daily feed intake; Nielsen et al.
If, in contrast, it is difficult to retain access to the feed (if competition is fierce), this may result in shorter and more frequent visits to the feed trough. Although enclosing the feeder makes access more difficult, it also protects the feeding animal, which is of importance when animal-to-trough ratio is high. It is interesting that feeding behaviour variables such as feeding rate and daily number of visits are now being considered in genome studies.
One aspect of feeding behaviour that changes in a social environment is the speed with which the food is ingested. Animals fed in a group-housed environment will increase their rate of eating even when this is not necessary to sustain a given level of intake. Pigs kept in groups of 20 have been found to eat faster than pigs in smaller groups.
This was not due to an overall time constraint, as there were times when the feeder was not occupied, even during daylight hours. Feeding rate may therefore be used as a tool to quantify welfare aspects of the social constraint affecting an individual pig within a group. It also highlights the motivation of social animals to synchronize their behaviour, including feeding, which is not possible if trough spaces are limited Behavioural synchrony may lead to a pig resting with its pen-mates instead of feeding from an otherwise available trough. This may contribute to the reduced feed intake found in group-housed compared with individually housed pigs.