Clinical and behavioural consequences of on-farm mixing of cull sows after weaning

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Highlights

  • In modern pig production, 50% of sows are slaughtered each year.

  • We examined mixing of cull sows and keeping them in groups of 3–4 for 24 h.

  • 24 h after mixing the sows showed signs of clinical deterioration.

  • During 6 h after mixing the occurrence of aggressive interactions was high.

  • Mixing of cull sows may challenge their welfare.

Abstract

In modern pig production up to 50% of the sows are slaughtered each year. Typically, the period from the decision to cull and until a sow is slaughtered consists of a stay in an on-farm pick-up pen (hours to weeks), transport (eventually passing buying stations or similar) and lairage. However, even though cull sows are often mentioned as vulnerable toward challenges such as transport, the behaviour and welfare of these animals have received very limited scientific attention.

The aim of this study was to examine clinical and behavioural consequences of keeping cull sows in on-farm pick-up pens before transport to slaughter. The observational study took place in a private Danish sow herd with loose-housed gestating and lactating sows. The study included 103 sows with a mean parity of 5 (range 1–9) and a BCS of 3 (range 2–3). On the day of weaning, the sows were examined clinically, and walked to pick-up pens in another part of the same building, each pen holding 3–4 sows. In the pens, the sows had free access to water from a water cup and were fed on the floor twice a day with a total 2.5 FU per sow. The mean room temperature was 21.0 °C (range 18–25.6 °C). After 24 h in the pick-up pens, the clinical condition of the sows showed signs of deterioration, as judged by an increased number of superficial skin lesions (median 0 (range 0−22) v. a median of 9 (range 0−75); P < 0.001) and increased gait score (median 0 (range 0−1) v. a median of 0 (range 0−2); P < 0.001). The median occurrence of aggressive interactions per pen during the initial 6 h post-mixing was 33, ranging from 11−55. Overall, the results suggest that a 24 h stay in a pick-up pen may be a challenge to the welfare of cull sows. Further studies are needed in order to understand effects of a stay in a pick-up pen, as well as other phases of the pre-slaughter logistic chain, on welfare during this period of the production cycle and to understand possible links to fitness for transport.

Introduction

Across countries with modern, industrialized pig production, an annual culling rate for sows of approximately 50% is not unusual (for example in Denmark (SEGES, 2019a) North America (Blair and Lowe, 2019) and discussed across countries (Tani et al., 2018)). The period from the decision to cull and until a sow is slaughtered is not well-described in scientific literature or industry guidelines (see for instance Blair and Lowe (2019) for a description of North American conditions or Herskin et al. (2020) for information obtained from a survey of Danish sow herd owners) but may consist of a stay in an on-farm pick-up pen (hours to weeks), transport (eventually passing buying stations or similar) and lairage. Even though cull sows are often mentioned as vulnerable toward challenges such as transport (Grandin, 2016; Fogsgaard et al., 2018; Thodberg et al., 2019), the behaviour and welfare of these animals have received very little scientific attention.

From other parts of the production cycle of sows, studies have shown that mixing of these adult females lead to aggression (Greenwood et al., 2014; Verdon et al., 2015), as they seek to establish new dominance hierarchies (Puppe et al., 2008), a process lasting 24−48 h, after which the level of aggression decreases and stabilizes (Marchant-Forde, 2010). Several studies have documented an increased risk of injuries due to inter-sow aggression in the hours/days after mixing (e.g., Greenwood et al., 2016; Büttner et al., 2015), constituting a challenge, economical as well as in terms of animal welfare (Ison et al., 2014).

According to Danish legislation, sows (including cull animals) must be kept loose and group-housed from weaning, and can only be kept isolated during four weeks after insemination (Anon., 2015). However, individual sows may be kept temporarily in pens or crates if sick, injured or highly aggressive. Loose-housed sows should be provided with at least 2.2 m2 per sow (if more than 6 per group), otherwise the legal requirement is 2.8 m2 per sow. Pens for sows have to accommodate facilities for cooling down by sprinkling, and to allow the sows permanent access to straw or other manipulable material (Anon., 2015). Hence, the legal requirements for sow housing are relatively simple, and may be achieved by use of several different types of housing. Currently, no rules exist for mixing of sows, and no recommendations are available regarding the use of this practice in the last days before the sows are sent to slaughter, which may seem paradoxical considering the documented negative consequences of this practice.

Despite a lack of scientific definition, the term ‘cull sow’ covers the period in a sow’s life from the farmer decides that she should leave the production herd and until she is slaughtered or killed on-farm (Anon., 2009). The movement of cull sows through the pre-slaughter logistic chain is not well-described, and may differ considerably between countries (see Blair and Lowe (2019) for a recent description of US-practice). In Denmark, a typical practice for farmers is to collect cull sows aimed for slaughter after weaning and keep them temporarily in crates or pens, while awaiting a group size of at least 10 sows before having them picked-up for slaughter, thereby limiting the transport costs per sow. To date, only very few studies have focused on how cull sows are managed (Herskin et al., 2020), and it is currently not known, how these animals respond to mixing.

The aim of this study was to examine clinical and behavioural consequences of keeping cull sows in on-farm pick-up pens before transport to slaughter.

Section snippets

Management and housing

This study involved 103 cull sows from a private Danish sow herd with crossbred Danish Landrace × Yorkshire sows. The size of the resident sow herd at the university did not allow studies like this, and consequently we recruited a private herd for the study. The recruiting of the participating herd was based on willingness to participate, as well as the relatively short distance between the herd and Aarhus. Data were collected weekly from July to December 2016. The sows were loose-housed during

Results

The study involved N = 103 cull sows with a mean parity of 5 (range: 1–9). The mean body condition score of the sows was 3 (range 2–3). Out of the 103 sows, 93 (90%) had normal hoof length and no sows showed signs of decubital shoulder ulcers. The results of the variables from the two clinical examinations are shown in Table 2. The 24 h stay in the pick-up pens led to a deterioration of the clinical condition of the sows, as shown by an increase in gait score (P < 0.001), increased proportion

Discussion

This study is among the first to focus on management and welfare of cull sows, and aimed to gain initial knowledge about clinical and behavioural consequences of mixing of cull sows – a typical practice in the days before slaughter. The results are based on data from 103 cull sows, from a private Danish herd with loose-housed sows in all parts of the production cycle. Directly after weaning their last litter, the sows were examined clinically before and 24 h after mixing with 2–3 other cull

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