Relative preference for wooden nests affects nesting behaviour of broiler breeders
Introduction
When attempting to optimise housing conditions for chickens kept on commercial farms, the main question is what does the hen prefer. Providing nests with a preferred design has benefits for the hens as well as for the producer. The welfare of the hens will likely be increased by meeting their needs and this could also increase the number of eggs laid in the nests as opposed to other locations. Eggs outside the nests are undesirable due to the time consuming manual collection and the reduced hatchability and saleability (van den Brand et al., 2016). This is caused by the fact that floor eggs are often dirty and broken, contain more bacteria on the eggshell and have more cracks than clean nest eggs (Berrang et al., 1997).
Relative preference or choice tests are the most used method to gain insight into the preference of the hens. Hens are offered two or more designs at the same time and their response to this is monitored for a certain amount of time. This response can be studied in terms of different parameters. The number of eggs laid in the nests is often used as a main parameter, as this clearly reflects a choice of the hens. Behaviour exhibited in and around the nest can also be used as a parameter. The term ‘settled’ has been used for describing nesting behaviour that would reflect a preference. Originally the term settled was used for a higher portion of time spent in the final laying position (Appleby, 1990; Appleby et al., 1993). More time sitting in the nest, especially in fewer bouts, is currently used more often as a measure for settled behaviour (Cronin et al., 2012). It has also been expanded to the searching phase, where fewer nest inspections and visits per egg are interpreted as more settled nesting behaviour (Freire et al., 1996; Hunniford and Widowski, 2018). Unsettled nesting behaviour can also be caused by negative social interactions, rather than a disliking of the environment. Aggression and displacement behaviour have previously been described in laying hens and can be disruptive to settled nesting behaviour (Freire et al., 1996; Struelens et al., 2008).
Previous research on the nest design preference of broiler breeders has shown that there is a preference for smaller metal nests compared to larger wooden nests, with unpainted rather than black painted walls (Brake, 1985; Holcman et al., 2007). Plastic materials, although commonly used in commercial practice, have not been compared to other materials before. Preferred nest size has also been studied, where smaller nests have been preferred over larger nests by broiler breeders as well as laying hens (Holcman et al., 2007; Ringgenberg et al., 2014). Although the preference of broiler breeders for type of bedding material was inconsistent, concave nest floors were preferred over flat floors and grey nest pads were chosen over other colours (Brake, 1993, 1985; Holcman et al., 2007). Seclusion is thought to be important for laying hens as pre-laying behaviour is more settled in the presence of nest curtains compared to no nest curtains, although no difference in number of eggs was found when comparing nests with sliced curtains to nests with one-piece curtains (Stämpfli et al., 2012; Struelens et al., 2008). In warmer climates, nests are often equipped with perforated nest floors to allow for air flow inside the nest. However, in colder climates chickens are observed to get disturbed by air flows in the nests as they might be sensed as draughts due to the lower temperature (Wim Peters, personal communication, 21 July 2017).
When the preferred nest has been found by hens, they tend to return to this nest every day. This conservatism in nest location has often been described (Appleby et al., 1984; Duncan and Kite, 1989; Riber, 2010; Riber and Nielsen, 2013), which has been suggested to be caused by the last remainders of broodiness, so as to form a clutch of eggs in the same location (Riber, 2010). To our knowledge, no study has investigated the response of hens when their usual nesting location becomes unavailable.
This study aims to compare four nest designs in a relative preference test. The most preferred nest was expected to be a nest with a partition in the middle, as this provides a smaller nest size and more seclusion. After that, we expected that the nest with wooden walls would be preferred over the control nest with plastic walls due to the natural properties of the material. The nest with a ventilator underneath was expected to be least preferred, as this creates an undesired air flow in the nest. Preference was hypothesized to be apparent in number of eggs laid in the respective nests, but also in more settled nesting behaviour. When closing the preferred nest at a later age, the hens were expected to move to the nest nearest their preferred nest independent of the nest design, which reflects their conservatism in location.
Section snippets
Animals and housing
The relative preference for nest design was tested with Ross 308 broiler breeders during the winter of 2017/2018. A total of 600 females and 54 males, all non-beak trimmed, were purchased from a commercial rearing farm with raised slatted areas at the age of 20 weeks. The chickens were randomly assigned to six pens, resulting in 100 females and 9 males per pen. The pens were identical in size (3.4 × 4.6 × 2.0 m, length × width × height) and layout and were placed in one row. The pens had wire
Distribution of eggs
During the course of the experiment 31,223 eggs were laid in the nests. The percentage of floor eggs over the entire experiment was 5.8 ± 2.8%. For the development of percentages of eggs in nests over time, see Fig. 1. The interaction between nest design and age was found to be significant (F27,2696 = 3.03, p < 0.0001). In week 23 the wooden nest did not differ significantly yet from the partition nest, but from then onwards there was a strong preference for the wooden nest. The overall
Discussion
This study shows a strong relative preference of the broiler breeder hens for the wooden nest. The large majority of the eggs were laid in the wooden nest and this suggests that the hens found this nest design best suited for egg laying, which is the ultimate purpose of a nest. The lower number of nest inspections (looking into the nest) and nest visits (entering the nest) per egg in the wooden nest compared to the other nest designs strengthens the suggestion that this nest is found to be more
Conclusion
From this study we conclude that a strong preference of broiler breeder hens for wooden nests over plastic nests is apparent, when offered in a relative choice test. This preference was demonstrated by a higher proportion of eggs laid in this nest and more settled nesting behaviour. It also led to crowding, causing piling and aggressive behaviour in the wooden nest. The hens were willing to accept this environment as they continuously returned to the nest. Closing the wooden nest led to a new
Acknowledgements
Many thanks to Gust Fleerakkers, Theo van der Wal, Annemieke Renders and Ronald Bax (Vencomatic Group BV) for their technical assistance and taking care of the animals. This work was supported by Vencomatic Group, Eersel, the Netherlands.
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