Cooling growing/finishing pigs with showers in the slatted area: Effect on animal occupation area, pen fouling and ammonia emission

Highlights

• Showers over the slats during warm periods decreased lying of the pigs in this area.

• Pen fouling was reduced with showers over the slats during warm periods.

• Ammonia emissions were reduced by 45% in rooms with showers.

• Improved animal environment due to better pen hygiene and lower NH₃ concentration.

Abstract

Growing and finishing pigs kept in insulated buildings are often exposed to high ambient temperature during summer. In high-temperature conditions, pigs in partly slatted pens change their behaviour to increase lying on the slatted area and fouling on the solid floor area, resulting in increased ammonia emissions. One way to cool the animals is to shower/sprinkle water in the slatted area, allowing pigs to wet their skin to increase heat loss. This study examined the effects of providing showers on pig activity and occupation area in pens, pen fouling and ammonia emission from the room. The investigation was performed in a commercial growing-finishing house with 10 identical rooms, each containing 16 pens for 9–13 pigs growing from 25–30 kg to 115–120 kg. Pigs were introduced into two parallel rooms in the house. During two summers and four batches, one room with showers in the slatted area and one room without per batch were compared in terms of concentrations of carbon dioxide (CO₂) and ammonia (NH₃), pig activity and occupation area in the pen, pen fouling and NH₃ emissions, recorded on four measuring occasions (M1–M4) during the growing period. Gas concentrations were measured using a photoacoustic analyser, pig activity and occupation area detected by machine vision techniques and pen fouling was visually investigated. Climate parameters (air temperature and relative humidity) were logged continuously during the entire growing period. Ammonia emission was calculated from ventilation rate (determined by the indirect CO₂ tracer gas method) and the difference in ammonia concentration between outlet and inlet air.

The results showed that the pigs spent less time lying on the slats (p < 0.05) and the solid floor was cleaner (p < 0.05) on measuring occasions M2, M3 and M4 in rooms with showers than in control rooms. Mean NH₃ emission for the four measurement occasions were 3.0–5.1 g pig⁻¹ day⁻¹ and 4.2–10.0 g pig⁻¹ day⁻¹ for the shower and control rooms, respectively. The differences were significant (p < 0.05) for all measuring occasions. The results also show improved animal environment when using showers to cool pigs at high ambient temperatures.

Overall, providing showers in the slatted area in partly slatted pens encouraged growing/finishing pigs to lie in the lying area, reduced problems with pen fouling and decreased NH₃ emissions by 45%. The latter could be partly due to reduced pen fouling and partly to dilution of urine on the slatted area and on the surface of slurry in the pit.

Introduction

Growing and finishing pigs in northern Europe raised in confined and insulated buildings with mechanical ventilation are often exposed to high ambient temperatures during summer. Even at maximum ventilation rate, the indoor air temperature in most buildings in summer may be around 5 °C higher than the outdoor temperature (Schauberger et al., 2000). When the ambient temperature exceeds the thermal comfort zone of pigs they become heat-stressed, which affects their performance, health and welfare (Banhazi et al., 2008). In a partly slatted pen with a lightly bedded lying area, the upper thermal tolerance level is 21 °C for growing pigs weighing about 30 kg and 17 °C for pigs weighing more than 50 kg (Hillmann et al., 2004). Periods with high ambient temperatures in such buildings will increase with predicted global warming (Schauberger et al., 2019).

Pigs are sensitive to high ambient temperatures since they only have a few active sweat glands. Above a certain temperature, they start to increase their respiration rate (Huynh et al., 2007), but their behavioural adaptation to wet the skin by wallowing in mud and water (Bracke, 2011) is restricted in conventional pig housing (Bracke and Spoolder, 2011). Huynh et al. (2007) argue that evaporative cooling from the skin is important for pigs, since evaporative heat loss from respiration reaches a limit at high ambient temperature and relative humidity (RH). They also claim that it could be more comfortable for pigs to increase wallowing than to increase panting. To improve animal welfare at high ambient temperatures, pigs need to be able to wet their skin in order to decrease heat stress (Huynh et al., 2007).

The natural behaviour of the pig is to have separate areas for lying and eliminative behaviour (Ekesbo and Gunnarsson, 2018). In confined pig houses, pigs use a defined lying area (most often with a solid floor) and a separate area for defecation and urination if the housing conditions are optimal. However, ambient temperature is one of several factors affecting behaviour such as lying, defecation and urination. When the ambient temperature increases above an inflection point, pigs start to lie more on the slatted dunging area in a partly slatted pen, as it tends to be a colder place to lie, increasing their heat loss (Aarnink et al., 2006; Hillmann et al., 2004; Huynh et al., 2005a; Savary et al., 2009). Pigs also lie more on their sides and less against other pigs at high ambient temperatures, to increase their heat loss (Aarnink et al., 2006; Hillmann et al., 2004). Increasing ambient temperature also increases wallowing by pigs in the mixture of faeces and urine on the pen floor (Huynh et al., 2005a). When pigs lie more in the slatted dunging area, the number of excretions on the solid floor area increases (Aarnink et al., 2006; Savary et al., 2009).

The behavioural elements behind fouling in pens are multifactorial (Larsen et al., 2018). Thermal climate and space allowance are important factors affecting pen fouling in an existing pen (Larsen et al., 2018). The number of excretions on the solid floor also increases above an inflection temperature (Aarnink et al., 2006; Huynh et al., 2005a). Below the inflection temperature, the number of excretions is low and not influenced by temperature (Aarnink et al., 2006; Huynh et al., 2005a). In addition, the proportion of urinations is affected by temperature. With increasing temperature, the number of urinations decreases, but the proportion of urinations on the solid floor increases (Huynh et al., 2005a). The amount of fouling also increases as pigs grow heavier (Aarnink et al., 2006, 1996; Hacker et al., 1994). Pigs require more space with increasing body weight and temperature (Spoolder et al., 2012). With a smaller area per pig, they spend more time in the slatted dunging area, which prevents access by other pigs (Hillmann et al., 2004). Narrow pens can also prevent pigs from moving to the dunging area because of other pigs blocking them (Randall et al., 1983). Due to insufficient area in the last part of the finishing period, pens are often fouled (Aarnink et al., 2006, 1996).

Pen fouling leads to impaired hygiene and air quality, increased NH₃ emission and extra work trying to keep the pen clean (Larsen et al., 2018). Ammonia emission from animal houses is also a multifactorial problem. Important factors affecting ammonia release include temperature and emitting surface area (Philippe et al., 2011; Sommer et al., 2006). Temperature has a direct effect on the release by favouring urease activity, biochemical degradation and volatilisation from the manure surface, but can also have an indirect effect via pig behaviour and pen fouling (Philippe et al., 2011). Pig houses with a partly slatted floor system have 25% lower NH₃ emissions than houses with a fully slatted floor system (Giner Santonja et al., 2017), owing to their smaller emitting surface area (Aarnink et al., 1996; Groot Koerkamp et al., 1998; Sun et al., 2008). However, some studies have found higher NH₃ emissions in houses with partly slatted floors during summer, due to pen fouling (Aarnink et al., 1995; Guingand and Grainer, 2001; Ni et al., 1999).

One method to cool the animals is by sprinkling or showering water in the slatted area, allowing the pigs to wet their skin with water. Use of sprinklers has been shown to reduce the amount of space that pigs need, as they lie less on their sides (Huynh et al., 2006; Spoolder et al., 2012). It could also prevent the increase in NH₃ emission due to pen fouling during summer. The aim of the present study was to determine the effect of showers in the slatted area in a commercial growing-finishing house with partly slatted pens regarding animal occupation area, pen fouling and NH₃ emission.