y se renueva frecuentemente Humedad constante entre 80 90%.

Perches, defined as elevated structures that birds can grasp with their feet and use to survey their environment from (EFSA 2015), are important recourses for chicken (Olsson and Keeling 2000). Night roosting is part of the natural anti-predator behaviour in chickens (Newberry et al. 2001). The use of perches by layer pullets promoted their skeletal development (Yan et al. 2014) and might also develop their spatial skills (Gunnarsson et al. 2000). Furthermore, access to perches at young age, before 4 weeks, lowered the number of floor eggs and reduced the risk of cloacal cannibalism in laying hens (Gunnarsson et al. 1999). Offering broiler breeders a perching possibility during the rearing phase reduced the number of floor eggs (Brake 1987) and alleviated fearfulness (Brake et al. 1994).

Equipping broiler houses with perches is one way of adding variety to the environment. Providing greater environmental complexity, with a possibility to perch, has been suggested to encourage increased physical activity of birds, which potentially leads to better leg health and welfare (Bizeray et al. 2002a, Ventura et al. 2012, Ohara et al. 2015). Furthermore, a change in exercise patterns brought about by barrier perches affected the development of musculature in broilers (Sandusky and Heath 1988a,b).

Environmental complexity could support more uniform use of the available space (Leone et al. 2007, Ventura et al. 2012, Cornetto and Estévez 2001a, Rodriguez- Aurrekoetxea et al. 2015), including the vertical dimension. An experiment conducted in commercial broiler breeder houses showed better spatial distribution of males, together with improvements in egg production, fertility and hatchability in houses furnished with cover panels. The researchers suggested that the presence of panels decreased stress levels and positively modified male-female contacts (Leone

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and Estévez 2008). The presence of vertical panels (Cornetto and Estévez 2001a, Cornetto et al. 2002) and barrier perches (Ventura et al. 2012) reduced disturbances between broilers and perching may also diminish aggressiveness among birds (Pettit- Riley et al. 2002, Ventura et al. 2012), depending on the perch design (Petit-Riley et

al. 2002). A further potential benefit of promoting perching in broilers in

commercial farming environments is that it can decrease contact between footpads and litter (Ventura et al. 2012). Under high temperatures, access to cool perches, compared with no perches, reduced the incidence of contact dermatitis and panting, and improved growth and feed efficacy despite less time spent eating and drinking (Zhao et al. 2013). An experiment providing broilers with a possibility to choose between cool and warm perches showed a preference for cooler perches, possibly due to enhanced thermoregulation (Estévez et al. 2002).

Comparing among perching studies is complex due to the various ways to assess it. However, most experimental studies on broiler perching indicate that perches are used only to a modest degree (LeVan et al. 2000, Su et al. 2000, Pettit-Riley and Estévez 2001, Tablante et al. 2003, Groves and Muir 2013, Kiyma et al. 2016), typically 1-3% of birds have been observed perching (LeVan et al. 2000, Su et al. 2000, Pettit-Riley and Estévez 2001, Tablante et al. 2003). Slow-growing broilers perched more frequently than fast-growing birds (Bokkers and Koene 2003). However, even in slow-growers, perching was highly inconsistent and depended on bird age and breed (Nielsen 2004, Lee and Chen 2007, Rodriguez-Aurrekoetxea et

al. 2015). Age

In layer chicks, the daytime use of perches begins at about 2 weeks of age, while perching at night starts to develop at about 3 weeks (Heikkilä et al. 2006). Also broiler breeders prefer night roosting on perches when given a possibility (Gebhardt- Henrich et al. 2016). Probably due to young age, diurnal rhythm does not seem to affect broiler perching (Hughes and Elson 1977, Martrenchar et al. 2000).

Age influences broiler perching rate (Hughes and Elson 1977, LeVan et al. 2000, Pettit-Riley and Estévez 2001). An early study showed increasing perching by broilers up to 8 weeks of age (Hughes and Elson 1977). However, because broiler growth performance has markedly increased over decades, those results hardly apply to modern fast-growing birds. According to more recent studies, broiler perching seems to reflect general activity since perch usage peaked at 4-5 weeks of age, declining thereafter (Bizeray et al. 2002a, Ventura et al. 2012, Bailie and O´Connell 2015).

Perch design and location

Several studies concluded that broilers are motivated to perch when offered an attractive opportunity to do so (Hughes and Elson 1977, Davies and Weeks 1995, Ventura et al. 2012). Perch design affects broiler perching (LeVan et al. 2000, Pettit- Riley and Estévez 2001, Oester et al. 2005). Modern broilers at older age might not be agile enough to use perches (Pettit-Riley and Estévez 2001), and easy accessibility could increase perching. An angled perch leading from floor to

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horizontal perches was shown to encourage perching (LeVan et al. 2000), however, not consistently (Pettit-Riley and Estévez 2001). A Swiss study demonstrated that instead of traditional perches, broilers more frequently used elevated platforms with ramp access (Oester et al. 2005). Also some laying hen strains demonstrated a preference for platforms over traditional wooden perches (Faure and Jones 1982).

Perch usage has been more commonly observed at higher densities (Hughes and Elson 1977, Martrenchar et al. 2000, Pettit-Riley and Estévez 2001), indicating that perching may be motivated by an attempt to avoid crowding. Not all existing data support this suggestion because higher density was reported to decrease all activity, including perching (Ventura et al. 2012). On the other hand, highest perching frequency was recorded at medium stocking density compared with lower and higher densities, depending on age and perch design (Hongchao et al. 2014). It was suggested that, at high densities, perching frequency could also be influenced by social factors (Pettit-Riley and Estévez 2001). The increased use of a central open area in a broiler house at higher densities (Leone et al. 2007, Ventura et al. 2012, Cornetto and Estévez 2001a) seems also to apply to perching: at lower densities broilers appear to favour perches located at peripheries, but at increasing densities perching is enhanced in the central area (Pettit-Riley and Estévez 2001).

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