The effect of a switch in housing systems on the welfare of gilts: does experience matter?
Abstract: In general, three approaches towards animal welfare exist: animal bodies, natures and minds. These concepts respectively emphasise physical health, natural behaviour and mental health. Each approach has its own corresponding welfare indicators. Knowledge in the area of especially the more persistent emotional states (mental health) of animals is lagging behind. This has to be improved, since the assessment of the emotional states of animals is a crucial step in improving their welfare. This study investigated the welfare of gilts before and after a switch in housing conditions (pens with concrete floor and pens with a wood shavings bedding) was made with a specific focus on their mental welfare. The first aim of this thesis was to investigate if the welfare of pigs housed under particular housing conditions (barren or on wood shavings) is influenced by their previous experience of housing conditions. The short and longer term effects of the switch in housing conditions on the pigs’ welfare were investigated. This was done by physical, behavioural and mental welfare indicators. The second aim of this thesis was to investigate whether the results of all three welfare indicators (animal body, nature and mind) lead to the same conclusions about animal welfare. For this purpose, 212 purchased gilts were used. The animals were kept from an age of four weeks (weaning age) until slaughter at ±24-25 weeks at the experimental farm Carus of Wageningen University. The experiment was set up using a 2 x 2 factorial arrangement, with housing conditions from weaning until 10 weeks of age (barren vs. enriched with wood shavings) and housing conditions after 10 weeks of age (barren vs. enriched with wood shavings) as factors. This resulted in the following groups: pigs housed for the complete experimental period on wood shavings (EE) or in barren pens (BB), pigs switched from barren pens to pens with wood shavings (BE) and pigs which were switched the other way around (EB). The switch in housing conditions was set at 10 weeks of age since the pigs were also used for a study that investigated the prevalence of Osteochondrosis which required this specific timing of the switch. However, for the present study, this timing was also very interesting since for fattening pigs, the switch from nursery to the growing-finishing phase includes a change in environment and normally also takes place at an age of approximately 10 weeks. With regard to the physical welfare (body approach), ulceration of the pars oesophageal region of the stomach was investigated post mortem, since stress is one of the causes of gastric ulceration. The behaviour of the pigs (nature approach) was investigated by continuous live observations for 4'10 min per pen per week when the animals were eight weeks old (before the switch), 10 weeks old (2-3 days after the switch) and 17 weeks old. The frequency of play (indicative of a more positive emotional state), manipulative and aggressive behaviours (indicative of a more negative emotional state) were scored. A startle response test, a gain of reward and a relative contrast test were used to investigate the emotional states of the animals in a more direct way (mind approach) compared to the nature approach. In the relative contrast test, for four consecutive days, the animals were given twice daily a reward with high incentive value (mix of yoghurt and chocolate raisins) followed by four consecutive days in which a reward with lower incentive value (their normal feed) was provided. Thereafter, for four consecutive days, the reward with high incentive value was again provided. This resulted in a total of 24 trials. A cue indicated that the treats were about to be provided to the pig in each trial. After a 15-sec time-interval in which the anticipatory response was investigated, the food reward was thrown into the pen. This was the start of the test phase, which lasted for 45 seconds, during which the response of the pigs to the reward was investigated. This test was conducted once, after the switch in housing conditions. With regard to the stomach scores, it was shown that post switch B (i.e. EB and BB) pigs had higher stomach scores, i.e. more stomach wall damage than post switch E (i.e. BE and EE) pigs F(1,28)=5.28, p=0.0292. Also the interaction of pre'post switch housing conditions tended to affect stomach scores F(1,28)=3.25, p=0.0823. Post hoc analysis revealed that EB pigs had a higher score than EE pigs with levels of BB and BE in between. Therefore, from the body approach, actual housing conditions seemed to be most important with enriched housed pigs experiencing a higher physical welfare compared to barren housed pigs. Experience of a different housing condition tended to be important, but only for pigs that were switched from an enriched to a barren environment (negative switch). The behavioural observations revealed that pigs housed in barren pens showed more negative (manipulative) and less positive (play) behaviour compared to pigs housed on wood shavings (all P<0.05). Also a slight effect of experience was present in some behaviours (pre'post or pre'post'week effects). However, no straightforward results were obtained in this regard, only minor indications of the importance of experience existed with regard to both a positive (steep decline in manipulative behaviour and delay of decrease of play behaviour) and negative (steep decline in play behaviour) switch. By means of behavioural observations, it was shown that from the nature point of view, indications existed that experience of either a barren or enriched housings system is important, but only for the short term. Actual housing seemed to be the most important determinant of the welfare of pigs with pigs housed on wood shavings experiencing a higher welfare compared to pigs housed in barren pens. With regard to the startle, gain and relative contrast test, it was shown that the relative contrast test gave the best indication of the mental welfare of the pigs. Enriched housed pigs showed more play behaviour in the test compared to barren housed pigs. They also seemed to be better in accepting the loss of reward and seemed to be less reactive and therefore less bored. Barren housed pigs seemed to be more bored, indicated by their high reactivity towards the presence of the observers, indicative of a less positive emotional state. They also seemed less capable of accepting the situation since they kept searching for the reward when their normal pellet feed was provided (all P<0.10). It was also shown that pigs that were switched from enriched to barren housing (i.e. EB pigs) were in a more apathetic state compared to pigs that were always housed barren (i.e. BB pigs). Based on the animal mind approach it could be concluded that actual housing seemed most important with pigs housed on wood shavings experiencing a better mental welfare compared to pigs housed under barren conditions. Also the importance of experience of housing conditions was shown, but only for a negative switch in housing system. Based on the results, it can be concluded that experience of housing systems does matter for the welfare of pigs. This was indicated by all three welfare indicators. It was shown that the results of the three different welfare indicators lead to the same conclusions. However, with regard to the body (stomachs) and mind (relative contrast test) approach: experience seemed to be mainly important when a negative switch was made, while the nature (behaviour) approach indicated that experience seemed to be important in both a positive and negative switch. Also, the time effect of the experience differed between the welfare indicators. The nature approach indicated that mainly a short term effect was present, while the body and mind approach indicated that also a longer term effect of experience was present. Therefore, it is recommended that all three welfare indicators are used to obtain a complete view of the welfare of an animal.
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