Rearing conditions and behaviour in pigs

anglais. During the last three decades the housing conditions of our livestock have been changed drastically (chapter 1). Amongst others, reduced floor space per animal and the monotony of the environment are the most striking changes.As in other animals, the actual situation strongly influences the behaviour of pigs. However, the effects of early experience on later behaviour in pigs are still not well documented. The aim of this exploratory study was to investigate these effects.In chapter 2 the design, the general material and methods of the entire series of investigations are described. To be able to distinguish the effects of early experiences (in casu rearing environment) on later behaviour, as clearly as possible, rearing conditions were chosen that differ greatly. Four litters of eight piglets each were reared in either a farrowing crate (the impoverished environment) or in a large straw pen (the enriched environment). The behavioural development during the first eight weeks of life and the differences therein for the two rearing conditions are described in chapter 3. The behaviour of the piglets was assessed by the focal animal observation method of individual piglets. Observations were made at fixed hours during day time.It was found that vital behaviours like ingestion (feeding, drinking and sucking) and resting were not strongly influenced by rearing condition. The same holds for nosing littermates, a behaviour that presumably plays an important role in mutual recognition. On the other hand, great differences between rearing conditions were discovered in exploratory and redirected exploratory behaviour (massaging or nibbling at littermates or sow). Piglets in the enriched environment showed more exploration than those in the impoverished condition. However, the development of exploration over the first eight weeks of life of the piglets was similar in both housing conditions; exploration increased with age. This might mean that the development of exploration is under endogenous control, while the level of exploration depends on the relative enrichment of the environment. Piglets in the impoverished environment performed much more massaging of or nibbling at littermates or sow than the piglets in the enriched condition. These behaviours are generally considered as redirected exploratory behaviours. The high amount of massaging of or nibbling at littermates and the restricted lying area presumably are the main causes of the high level of restlessness (standing and sitting) of the piglets in the impoverished environment.After eight weeks of rearing, six piglets per litter went to a commercial fattening farm and two gilts per litter were kept for breeding. The fattening pens had a full slatted concrete floor. For the pigs reared in the farrowing crate these pens embodied a relatively enrichment; the floor space was larger and a plank at the bottom of a welded mesh gate proved to be an excellent object for biting, nibbling or chewing. For the straw reared pigs the fattening pens were a relative impoverishment of the environment. During fattening the behaviour of the pigs was assessed by means of 24 hour time-lapse video recordings (chapter 4), which were also made during rearing. From an age of two weeks onwards a diurnal activity rhythm was found independent of rearing conditions. The similarities and differences in behaviour in the two rearing conditions obtained by means of the focal animal observation, described in chapter 3, were found also by means of these video recordings. The relative enrichment of the fattening pens increased exploration in the crate reared pigs. In straw reared pigs the opposite was found. It was argued that because of the experience with a simpler environment the crate reared pigs needed more time than the straw reared pigs to assimilate the new environment. In spite of the low level of redirected explorative behaviour during rearing, the straw reared pigs showed as much of this behaviour during the fattening period as did the crate reared piglets. Thus, massaging of or nibbling at littermates appeares to be almost completely determined by the actual situation. The high level of restlessness found in crate piglets persisted over the entire fattening period (till the age of 24 weeks). Although restlessness increased in straw reared pigs during fattening, these animals' score was always lower than that of the crate reared ones.In chapter 4, a measure for the synchrony of activity is defined; if n is the number of animals in a pen, than n states or classes ofactivity are possible namely 1, 2, 3 n animals being active simultaneously. The measure of synchrony of activity was defined as the ratio of the occurrence of class n (all animals active) divided by the sum of occurrence of all classes (1+2+3+.....+n).During the first eight weeks of life straw piglets showed a higher synchrony of activity than the crate piglets. Thereafter this difference was not as clear. A strong negative correlation was found between massaging of or nibbling at littermates (SN-pig) and the synchrony of activity. After ruling out the age effect, this correlation was still high; in the first eight weeks r=-0,87 and in the fattening period r=-0,81. Thus, a high synchrony of activity reduces the probability of SN-pig and hence of restlessness.After having been reared for eight weeks in the two different housing systems, two crate reared gilts and two straw reared ones were housed in a large straw pen and inseminated in their second oestrus. Fourteen days before the expected farrowing date the gilts were housed individually in a straw pen. The behaviour of these gilts during day time was observed from five days before till 13 days after farrowing (chapter 5).With respect to nursing (that is, the animal is lying on the side with fully exposed udder and more than half of the total number of piglets is active at the udder) on the first day after farrowing more nursing in straw reared gilts than in the crate reared ones was found. No further differences in behaviour were found between crate or straw reared gilts before and after farrowing.During farrowing crate reared gilts showed more restlessness than the straw reared gilts. This difference was already visible on the first day before farrowing. Obviously, the acquired restlessness persisted even after having been housed in an enriched environment for ten months.Data from six hours continuous observation during farrowing were submitted to a sequential and cluster analysis. Straw reared gilts showed two clear clusters of behaviour:1) Behaviours directly involved in the farrowing process: sliding into, lying, nursing, delivery and expelling of the placenta.2) Behaviours directed towards the physical environment: nestbuilding, standing and sitting, and exploration.In crate reared gilts one great cluster was found in which sliding into, lying, nursing, delivery of the piglets and expelling of the placenta were taken together; this cluster also contained nestbuilding, comfort behaviour and biting and snapping.Another cluster was formed by standing and sitting, and exploration. From the sequential analysis it was clear that crate reared gilts more easily switched from behaviours involved in the farrowing process itself to behaviours that interfere with the farrowing process.During the first eight weeks of life standing and sitting appeared to be good strategies to avoid or to escape from being massaged or nibbled at; the animals also learned that unpleasant or stressfull situations can be avoided this way. However, this standing and sitting behaviour which also occurred during farrowing as reaction to a novel stressfull situation, is not very adaptive in terms of survival value for the offspring. Because the duration of farrowing did not differ between crate and straw reared gilts, both groups of gilts were probably equally stressed. If this is so, the differences in behaviour found during farrowing can not be attributed to differences in amount of stress experienced by crate and straw reared gilts respectively.From the results of the study presented in chapter 3 (differential rearing) it appeared that two major factors - bedding and floor space - influenced the behaviour of the piglets.In chapter 6 the effect of bedding (straw) on the behaviour of piglets is described. Four litters of eight piglets each were housed in farrowing pens; the sows were tethered. During the first two weeks of life two litters were provided with a straw bedding while two other litters were not. From the third week on the substrate was exchanged every week from straw to bare floor and vice versa. It appeared that active behaviour of the piglets strongly depended on the presence or absence of straw. When straw was not available, the piglets immediately directed their exploratory behaviour towards littermates and sow. The piglets also became more restless (more standing and sitting) and started agonistic behaviour more easily. Furthermore, it became clear that the total amount of exploratory and redirected exploratory behaviour performed on a bare floor did not reach the level of exploratory behaviour of piglets of the same age on straw. This suggests that exploratory behaviour in a barren environment cannot be satisfied fully by alternatives or redirected behaviours as used by the piglets. In chapter 7 the effect of pen size on the development of agonistic behaviour in piglets is described. Three different pen sizes were used: 1) 28 m 2with a loose sow; 2) 6.7 m 2and 3) 3.5 m 2; in the latter two the sow was tethered. All pens contained straw bedding.By using a fine grained ethogram of agonistic behaviour and applying sequential analysis, several differences between the pen sizes were found in the development of agonistic behaviour.As already shown in chapter 3, pen size did not influence the development of individual recognition (nosing littermates). However, there were significant differences in the development of agonistic behaviour. Piglets housed in pens of 3.5 m 2did not develop threat behaviour (standing in front), did not learn to inhibit biting and to place headknocks exclusively on the head or shoulders of other piglets. Typical sequences of agonistic behaviour were also different for the three sizes. After week 4, in the largest pen 37.8% of all headknocks were preceded by threatening, in the 6.7 m 2pen it was 29.5% and in the 3.5 m 2only 3.9%. In the 3.5 m 2pen more than 40% of headknocks were preceded by exploration or other unspecified behaviour. Because threat behaviour lacked almost entirely in the piglets in the smallest pens, the start of an agonistic interaction was highly unpredictable for this group of animals. This unpredictability of the behaviour of littermates further contributed to the restlessness in these cages. Unlike the piglets in the 6.7 m 2and 28 m 2pens, the piglets in the smallest pen did not change the pattern of their agonistic behaviour anymore after week 3. Therefore, the agonistic of the latter piglets may be classified as infantile; presumably, this will not improve later in life. Therefore, these piglets must be considered to be not very well equiped for social grouping as adults.In the general discussion (chapter 8), two main points are selected for a more detailed discussion: first, the immediate effects of rearing in different environments on the behaviour of piglets and secondly, the effects of this differential rearing on later behaviour around farrowing.The amount of floor space mainly influenced the development of agonistic behaviour. The complexity of the environment and especially the presence of bedding proved to be an important factor in preventing the occurrence of redirected explorative behaviour and restlessness. From the findings described in chapter 3 and 7, it is argued that the socialization period of piglets falls in the second and third week of life. The effect of reduced floor space, increased unpredictability of the behaviour of conspecifics, and strongly resembles the effect of social isolation as found in other species. In both situations the animals do not learn to control their social environment.Impoverishment of the environment causes redirected exploratory behaviour. The piglets learn to deal with this behaviour of their peers conspecifics by avoidance or escape reactions, mainly consisting of standing and sitting. In later life the same animals showed regression of this behaviour, in that they performed the same response in reaction to a novel and stressfull situation like farrowing. This type of response is maladaptive in this situation because of possible detrimental effects for the piglets.Environments inducing redirected exploratory behaviour and preventing the development of social skills do not contribute in a positive way to the welfare of the animals. For practical pig breeding the rearing situation might be very important because of its effects upon the behaviour in later life of the animals.

néerlandais; flamand. Via vergelijkend gedragsonderzoek bij biggen in hun eerste levensweken is onderzoek gedaan naar de invloed van de wijze van huisvesten. Vier tomen van elke acht biggen groeiden op in een kraamopfokhok (met roostervloer) en een gelijke groep dieren in een ruim strohok. De eerste groep (arme omgeving) vertoonde meer masseren, bewroeten, besabbelen en beknabbelen van toomgenoten, terwijl de tweede groep meer onderzoekend naar de omgeving was. Bij overplaatsing van beide groepen naar een mestbedrijf in kale hokken met roostervloeren behield de tweede groep een stabieler gedrag. Dit verschil in gedrag was ook waarneembaar in een soortgelijk vergelijkingsonderzoek onder gelten: de gelten die opgroeiden in strohokken werkten hun nesten beter af en waren rustiger tijdens het werpen van hun eerste toom biggen