Chickens with free-range access often make limited use of their free-range area; a small part of the flock is usually observed outside at any given time, and those that are outside prefer to stay close to their houses. As a consequence, the claimed welfare benefits of free-range use may not be achieved, and nutrient loads in the soil are very high close to the chicken houses. The low range use may have several reasons, such as fear of a novel environment, adverse weather conditions, or low motivation to explore. This thesis aimed to assess the effects of combining slow-growing free-range broiler chickens with short rotation coppice willows (SRCW). These are fast-growing trees that are used for biomass production. They could provide a good ranging environment to the chickens, and be an extra source of income for the poultry farmer. It was assessed how SRCW and artificial shelter influenced free-range use, leg health, fearfulness and meat quality. In addition, two rearing strategies were tested aimed at improving free-range use. Furthermore, a new system was developed to automatically monitor free-range chickens’ position. Finally, the interactions between chickens, SRCW and soil parameters were assessed. 

Factors affecting and being affected by free-range use

In Chapters 2, 3 and 4 the relationships between free-range use and shelter types were studied. In Chapter 2, slow-growing broiler chickens (Sasso XL451) were given outdoor access either to an area with grassland and artificial shelters (wooden A-frames; AS) or to an area with SRCW. In all studies in this thesis, birds were given outdoor access approximately between four and ten weeks of age. The groups with access to SRCW had higher mean percentages of birds outside (42.8% vs. 35.1%), and more birds that ranged farther than 5 m from the house (10.6% vs. 4.1% of all birds outside). In Chapters 3 and 4 the birds were given access to both AS and SRCW. This revealed that birds had a strong preference for SRCW, with more birds ranging in this shelter type and with birds going farther from their house. In Chapter 4, an additional shelter type was provided, i.e. overhangs adjacent to the pop holes. It was hypothesised that these would result in a more gradual transition between the indoor and outdoor environment, and therefore in more free-range use. However, no such effect was found, neither were overhangs related to a difference in the behaviours that the birds displayed.

The effects of weather conditions on free-range use were studied in Chapters 2 and 3. If birds had access to either AS or SRCW (Chapter 2), rainfall, increasing solar radiation and increasing wind speed were negatively related with the number of birds outside, and these effects were more pronounced in SRCW. This could indicate that SRCW provides less protection against these weather conditions than the A-frames, but possibly this result was due to more birds being outside in SRCW, so more birds could go inside during adverse weather. If birds had access to both AS and SRCW (Chapter 3), rainfall and decreasing solar radiation were related to finding more birds outside in AS, whereas the opposite was true in SRCW. This suggests that SRCW provides better protection against solar radiation than AS, and that birds chose to seek shelter in the vegetation instead of in their house if they have the opportunity. In this case, increasing wind speed was related to less birds outside in both shelter types. In both chapters, an increasing temperature was related to more birds being outside.

The relationships between free-range access and fearfulness and leg health were studied in Chapter 2. In addition to the birds with access to either AS or SRCW, there were also groups that were kept indoors (IN) for the entire production period. In week 3 (i.e. before outdoor access was provided), birds were subjected to a tonic immobility (TI) test (gives an indication of the level of fearfulness), and this test was repeated in week 10. A longer TI duration in week 3 was associated with more birds farther than 5 m from the house, but not with the mean number of birds outside. TI duration in week 10 was not associated with either of these, but the number of inductions needed was higher in SRCW than in IN groups. These findings suggest that there is a negative relationship between fearfulness and free-range use, but more studies, e.g. on individual birds’ data, are needed to confirm this. Gait problems tended to occur more in IN than in AS birds, and hock dermatitis occurred more in IN than in AS, and tended to occur more in IN than in SRCW.

The behaviours of the birds in relationship to the shelter types were studied in Chapters 3 and 4. This revealed that relatively more birds were foraging in AS, but because the total number of birds was always higher in SRCW, the absolute number of birds foraging was also higher in SRCW. Foraging occurred more at >5 m from the house than closer by, possibly due to depletion of vegetation in proximity of the houses. Sitting occurred more close to the houses, and in SRCW, which may be attributed e.g. to a more favourable microclimate or a greater sense of safety due to more cover.

In Chapters 3 and 4, two rearing strategies were tested: providing environmental enrichment and providing access to dark brooders early in the chickens’ lives. Both were provided from day 0 until the birds were moved to mobile houses in week 4. The enrichment consisted of hay bales, scattered grain, strings and live mealworms. Dark brooders are warm, dark, secluded areas in the home pen under which the chicks can rest. There are indications that both environmental enrichment and dark brooders have the potential to decrease fearfulness and increase exploration motivations, which could subsequently lead to better free-range use later in life. In the present study, the enrichment and dark brooders had no relevant effect on TI duration or free-range use. The dark brooders only tended to affect the number of birds that jumped in an open field test (higher in non-brooded birds). No effects of the dark brooders on behaviour of the birds at later age could be demonstrated, and only minimal effects of the enrichment on behaviours were found.

In Chapter 5, the effect of free-range use on production and meat quality was assessed. The treatment groups used were the same as in Chapter 2 (IN, AS, SRCW). At slaughter age (d72), IN birds were heavier than AS and SRCW birds, but no differences in feed intake or feed conversion were found, possibly due to unregistered feed intake (vegetation, insects, small vertebrates) by the AS and SRCW birds in the free-range areas. Breast meat of chickens with free-range access was darker and yellower than that of IN chickens. Ultimate pH was lower and drip loss higher in IN versus AS chickens. The percentage of polyunsaturated fatty acids was higher in AS than in IN meat. A blinded taste panel judged breast meat of SRCW chickens to be more tender and less fibrous compared to that of AS and IN chickens, and juicier compared to the IN chickens. 

Automated positioning system

Chapter 6 describes the performance of a newly developed automated positioning system to monitor free-range chickens’ position. This Ultra-Wideband (UWB) system consists of active tags (attached to the chickens) that send signals to anchors positioned at fixed locations in the field; the tags’ position can be calculated using the time of arrival of its signal, if this is registered by at least three anchors. Its accuracy and registration success, as well as which factors may affect its performance, were assessed. The effects of vegetation type, precipitation, tags being mounted on a chicken, tag height, angle and orientation, coverage by A-frames or mobile chicken houses, and proximity of other tags on accuracy of the registered positions (distance between the registered and the true position of the tag) and on registration success (percentage of registrations where a position could be calculated) were assessed.

Overall, the median error was 0.29 m, and the mean percentage of successfully registered positions was 68%. None of the variables had a clear effect on the accuracy of the positions. Errors were generally larger in certain areas of the experimental field, which may be due to the asymmetrical setup of the anchors. The percentage of successful registrations was negatively affected by shelter type, with lower percentages in dense vegetation (short rotation coppice willows) than on grassland, possibly due to malfunctioning of two anchors close to the SRCW plots. Rain and placing the tags underneath a wooden A-frame, but not placing them in a mobile house, resulted in a lower percentage of successful registrations. The tag being mounted on a chicken, height and angle of the tag and proximity of other tags had no negative effect on the percentage of successful registrations. Placing more (functioning) anchors may contribute to better accuracy and registration success. Alternatively, the bias resulting from the variables that had a negative effect on registration success should be corrected for when using the system in its current setup. Overall, this system shows great promise to be used for monitoring chickens’ free-range use. 

Interactions between chickens, SRCW and soil parameters

In Chapter 7, the interactions between slow-growing broilers, SRCW and soil parameters were studied. The experimental field was split up into four quadrants: two were sown with a grass/clover mixture, two were planted with SRCW (three clones, i.e. Tora, Tordis and Klara) and clover as undergrowth. SRCW was harvested 1 and 4 years after establishment. Chickens were present on the field during parts of each year (see Chapters 2, 3 and 4), and parts of the field were kept chicken-free as a control. Free-range use, SRCW growth and soil parameters were monitored on a regular basis over a 4-year period.  No effects of chicken presence on SRCW growth were observed. Total mineral N (Nmin) was affected by vegetation type x location x depth; it was generally higher in SRCW than in grassland, in areas close to the chicken houses, and in more superficial soil layers. This could be due to return of N through leaf fall, as opposed to grass which is mown and removed. SRCW was also harvested eventually, but the amount of N removed through this process was lower than that removed by mowing the grassland. In addition, higher Nmin levels could be due to the higher chicken density in SRCW (more N deposition through faeces), to NH3 being captured from the air by the trees, to the strong clover development under SRCW (which can fix atmospheric N), and to the lower N requirement of SRCW compared to grassland. Nmin did not appear to accumulate in the soil over the years, but close to the chicken houses there were indications for nitrate leaching to deeper soil layers and possibly to groundwater. K and P- CaCl2 were higher close to the chicken houses, probably due to high concentrations of these nutrients in chicken faeces. No increase in soil organic C was observed over the four-year experimental period, and no differences were found between SRCW and grassland. This could be due to the short time period that SRCW was present. In conclusion, SRCW was preferred by the chickens, but the possible leaching of nitrate to ground water close to the houses and possible remediating strategies for these need to be studied further.  

Conclusions

From this thesis it can be concluded that SRCW and broiler chickens can be combined in order to promote free-range use: birds preferred SRCW over AS, and ranged further from their house in the former, without having an effect on SRCW production. Overhangs adjacent to the pop holes were not successful in promoting free-range use. The provision of environmental enrichment or dark brooders early in the birds’ life did not affect free-range use later in life. Free-range access may be associated with better gait and less hock dermatitis, as well as with changes in meat quality such as a more pronounced yellow colour and more tender and less fibrous meat. Individual free-range use monitoring would possibly elucidate these relationships further. The automated positioning system that was developed showed promise for use in future research. There could be some bias between different vegetation types, with tags in SRCW being detected less often than those in grassland, although this was probably at least partially due to problems with anchors next to the SRCW plots. Combining broiler chickens with SRCW resulted in high levels of N and P in the soil, especially close to the chicken houses. This can result in leaching of these nutrients to groundwater, and calls for further research.