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The Poultry Code of Practice Scientific Committee Report, which preceded the Code of Practice and provided a review of current literature on select topics, was completed in 2013. In that report, a specific section on
“Enrichment” was not included, however the increase in research (demonstrating an interest in this area) has increased substantially since the 2013 document was published (Table 1). As a reminder, during the drafting of the Science Report, the scientists were asked to report on the peer-reviewed literature, without making recommendations based on that literature. This current report now includes as many of the papers as this author could find from 2014-2020.
Since an enrichment document was not included in the 2013 Science Report, results for this report have been sectioned into the three categories given in Fraser’s three circles, which were used in the 2013 report (Biological Functioning, Affective States, and Natural Living), and conclusions, based on peer reviewed literature only, are included at the end of the report. Once again, these are not recommendations. While the earlier papers focused primarily on biological functioning, the more recent papers focus primarily on emotional health, preference etc. of the birds.
“Enrichment” definitions vary, but essentially this generally refers to “an improvement of the environment of captive animals, which increases the behavioral opportunities of the animal and leads to improvements of the biological function….” (Riber et al., 2018). The purposes of these include an improvement to biological functioning, and stimulation of the brain with can result in a reduction of stress.
Enrichments are often discussed with relationship to a number of benefits. These include increasing activity, which, with respect to biological functioning, is then often related to improved bone or leg health, and reduced severity of pododermatitis. Some of the research from 2014-2020 supports this, while other research programs do not, and this may be dependent on the type of enrichment tested. There are many, so these have been separated when possible below.
Perches provide enrichment for leghorn birds, with a high percentage of those birds utilizing them. However, research with broilers appears to differ with regards to the birds preference for perch use (see behaviour section below). A number of papers have tested perches for broilers with respect to biological functioning. Kiyma et al. (2016) tested the effect of perches vs no perches on performance and health parameters in commercial Ross 308 chickens. Their results indicated that approximately 7.36% of broilers used perches. No differences in growth were noted in response to the treatment, but footpad lesions were lessened when birds had perches in their environment. No effect was found on carcass weights, however breast meat appeared less red when perches were included in the pens. The authors concluded that perches can reduce the effect of footpad lesions, and may reduce inflammation of the breast muscle, which can result in an increase in redness.
Another study, by Aksit et al. (2017), examined broilers (700 Ross 308 mixed sex) with and without perches, in combination with fluorescent vs LED lighting. Although these authors found a reduction in early body weight when LED lighting in combination with perches was used, there was no effect at 42 d of age. No differences were found in tibia breaking strength, suggesting that movement up and down to the perches did not improve bone quality. This was supported by no differences in gait score. Perching did impact meat colour, with breast muscle having more yellowness/redness compared to that found in broilers without perches. This latter data is the opposite of what was noted in the Kiyma et al. (2016) paper.
A large study was performed where broilers were given access to either perches, platforms or no enrichment devices (Kaukonen et al., 2016). Data were collected on four commercial farms, with 4-6 flocks tested per farm. Producers kept track of usage of the enrichment devices. Once again, the perches were rarely used, and that treatment was removed from the study. However, producers found that 50- 100% of broilers used the wider platforms. The results showed that leg health was significantly better when broilers had platforms compared to no enrichment devices (improved gait score, tibial dyschondroplasia frequency and severity).
However, not all studies have found improvements in leg health when platforms were tested. Bailie et al. (2018) tested different types of perches in addition to platforms on the health of broiler legs. With respect to leg health, the authors concluded that no improvements resulted from platform or perch use. In addition, Kaukonen et al. (2017b) tested broilers reared with platforms to those with no enrichment device. They found no negative effect of platforms on foot health or hock skin condition, but also reported no improvements.
The previous data clearly has indicated that broilers prefer a grid or platform as compared to standard perches. Baxter et al. (2020) then focused on determining space requirements of perches for broilers as compared to a control treatment. With respect to productivity and health, fewer birds were noted as having severe leg disorders in the broiler groups with the longest perch level per bird, however no effect was noted for gait scores. No differences were noted for other production parameters or other health parameters.
Bailie and O’Connell (2015) tested broilers (four barns, replicated 4 times) with or without string, and with or without perches, on a number of parameters. With respect to biological functioning, the authors found that walking ability (gait score at 3 and 5 wk of age) was improved with string allowance.
Yildirim and Taskin (2017) tested the effect of a number of types of enrichment, as compared to a control group with no enrichment, on 280 Ross 308 mixed sex birds. Their enrichment treatments included the addition of a perch, or a ball, or mirrors or dust, and these were tested to 42 d of age. The enrichment techniques had no effect on productivity parameters, including weight gain. There was also no effect on lymphoid organ weights, or rectal temperatures at 21 or 42 d of age. However, in this study, all enrichment groups had an improvement in gait score, suggesting that leg health improved with the addition of any of the enrichment additions.
De Jong and Gunnink (2019) tested combinations of enrichment devices. In their study, groups of broilers were either housed in a control group with no enrichments, enriched groups (bales, perches and metal pecking chains) without natural light, or enriched groups with the addition of natural light. The enrichment groups had no effect on lameness, footpad dermatitis, hock burn, cleanliness or injuries.
Two studies on ramps have been conducted by Ruiz-Feria et al. (2014). These authors tested the effect of ramps, and the distance between feed and water, on bone and tendon strength, and productivity of Ross 708 broilers. Their first study tested distance between resources of 1.0, 3.3 or 6 m. These distances had no effect at 49 d of age on bone breaking strength, latency to lie (measure of leg health), footpad lesions or body weight. Birds that had to walk further did have less abdominal fat. In their second experiment, treatments, tested on male Cobb chicks, included 2 distances and ramps (with or without). Treatments did not significantly affect bone breaking strength, but birds given ramps had lower tendon breaking strength than did the broilers without ramps which suggested poorer tendon integrity. Latency to lie (measure of leg health) was longer with no ramps. The authors’ conclusions were that distance had little impact on leg health parameters measured, and that the presence of ramps had a negative effect on tendon integrity.
Square bales can be an easy source of enrichment for broiler barns. Bailie and O’Connell (2014) allowed broilers (two 23,000 bird barns) access to either 45 bales per house, or 30 bales per house. This study was replicated over 6 flocks. In this case, increasing the number of bales had no effect on ability to walk in the gait score test, but the latency to lie (bird is encouraged to stand) was longer in the 30 bale group, suggesting poorer leg health. No differences were found in any productivity data, nor in general behavioural activity, suggesting that increasing the bale numbers did not significantly improve welfare.
A group in Japan tested presence of hay bales and perches together, compared to no enrichment, with broilers on a wide sector of variables. Testing 4 houses and approximately 21,500 birds, this group found a reduction in footpad lesions for female birds only, but not males, when bales and perches were included (Ohara et al., 2015).
Another trial tested the impact of straw bales, oat hulls or straw bales and oat hulls as enrichment devices (in an attempt to encourage dustbathing activity) on performance and behaviour of commercial broilers (Baxter et al., 2018b). With respect to performance, no differences were noted on body weight, litter quality, atmospheric quality or footpad lesions. However, broilers that were given oat hulls, or oat hulls and bales, had improved gait scores compared to those given only bales, indicating an improvement in leg health.
Vasdal et al. (2019) examined the impact of a number of enrichment treatments, as compared to no enrichment, on gait score and behaviour of broilers. The treatments included peat, hay bales and elevated platforms. Gait score was examined as a measure of leg health, and the study found a trend (P=0.07) for any enrichment treatment to result in broilers with improved leg health.
Pederson et al. (2020) focused their study on whether 8 types of enrichment, compared to an unenriched control, would improve bone health and muscle characteristics of broilers, including if allowing enrichment would impact breast muscle myopathies. Placing 7 m between feed and water resulted in a wider tibiotarsus bone than birds with straw bale enrichment. Vertical panel placement in the pens resulted in wider leg muscles compared to treatments with roughage, 3.5 m between feed and water and straw bales. No other effects were noted, including any effects on wooden breast or bacterial infections. The authors concluded that some enrichments may improve health via wider bones and larger muscles.
An interesting study was conducted by Meyer et al. (2019) in which they tested a novel enrichment device – laser beams to the floor, and compared those broilers to control broilers without enrichment from 0-42 d. The laser was believed to simulate predators. The data showed the laser treatment birds had higher feed intake and daily gain, improved feed conversion ratio, and heavier market body weights. However, no effect was found on footpad lesions, breast blisters, tibia quality or environmental parameters.
A study examining the effect of giving sound (music) and LED lights (red or blue strobe lighting) for 6 min per day on body weight was conducted by Jacob et al. (2020). The results showed that birds exposed to the light enrichment were the lightest, while the heaviest body weights were noted in broilers given no enrichment at 35 d of age.
A number of studies have been conducted with flooring systems or litter types, with the authors describing these as “enrichments”. It is not clear if all of these would meet the definition of enrichments however.
Litter based “enrichments” have been tested with respect to impacts on productivity. Kaukonen et al. (2017b) tested broilers reared on wood shavings, ground straw bedding and peat. Their results indicated that footpad health was improved when broilers were reared on peat compared to wood shavings or ground straw. Litter moisture did not differ between peat and wood shavings at the end of their trials. The authors concluded that peat is a viable source of litter, but also stressed the importance of litter management.
A study conducted over 4 flocks of broilers compared productivity parameters of broilers housed on conventional litter compared to a netting system. No effects of floor system were noted for body weight, FCR or feed intake. However, the netting flooring resulted in an increase in breast blisters (Li et al., 2017).
Perforated flooring has also received some interest as enrichments. Alves de Almeida et al. (2017) tested broilers housed on traditional wood shavings compared to plastic perforated flooring. The results included higher levels of ammonia and CO2 in the wood shavings treatment. Meat production was higher for males, but numerically highest when reared on perforated flooring. Birds reared on perforated flooring were cleaner and had improved hock condition, but no differences were noted on breast lesions.
With the objective of improving footpad lesions, Chuppava et al. (2018) tested four different flooring systems, some of which may add environmental complexity. These authors tested litter flooring, litter with floor heating, a partially (50%) slatted floor with litter, and a fully slatted floor with a sandbath area. Body weight of broilers was higher when reared on the fully slatted floor, but no other effects were noted, including on footpad health.
Ross 308 broilers reared in barns with 50% perforated flooring under the feeders and drinkers were compared to broilers reared in wood shavings houses for productivity and health parameters (Adler et al., (2020). The results showed that broiler footpad dermatitis at d 14 and hock burns at 28 d were worse in houses using wood shavings, compared to the partial perforated flooring systems. No differences in body weight or other productivity parameters were noted.
With respect to affective states, enrichments are meant to stimulate the brain, increase positive behavioural expression, and reduce fear and stress. As with biological functioning, a number of enrichment techniques have been tested, and these are outlined below.
Fear is a common affect believed to be impacted by enrichment techniques. Studies with perches have not always found this result. For example, Aksit et al. (2017) tested broilers housed with or without perches, and with LED vs fluorescent lighting. The authors used tonic immobility, which tests how long a bird remains in a tonic state after induction. The longer time in a tonic state, the higher the fear level is thought to be. These authors found no differences in tonic immobility length when perches were or were not utilized.
For an enrichment device to function as planned, it must be utilized by the birds. Norring et al. (2016) tested the use of perches vs plastic platforms vs control barns in broilers. Their results indicated that broilers significantly preferred platforms over perches, and that low perches (10 cm) were preferred over higher perches (30 cm), indicating a strong motivation to use the platforms. Interestingly, overall activity did not increase when platforms were provided.
Bailie et al. continued this work in 2018. These authors tested six perch types with respect to preference. Their research clearly demonstrated that birds had a preference for platforms in comparison to perches, and even within perch types, birds preferred some types over others, particularly those with a ramp.
Baxter et al. (2019) compared emotional states of broilers housed with platform perches, platform perches and peat dustbaths, or unenriched controls through video analyses of behaviour at weeks 3, 4 and 5. Their results showed that fear levels were lower when any enrichments were provided compared to broilers housed in an unenriched environment. These authors were one of the first to assess play behaviour, as it suggests improved welfare (frolicking, sparring and food running). However, they found that enrichments did not increase the amount of play demonstrated.
Ohara et al. (2015) focused their work on the use of perches and bales. The utilization of these enrichment devices decreased with age of broilers. However, regardless of the age, activity increased with use of the perches and bales, with less time sitting in the litter. Their work also tested stress levels on Japanese broilers via heterophil/lymphocyte (H:L) ratios at 3, 5 and 8 wk of age. The authors reported a reduction in H:L ratios in the younger birds when bales and perches were given (indicating reduced stress).
Vasdal et al. (2019) observed behaviour at 16 and 30 d of age of broilers that were provided one of four treatments: peat, hay bales, elevated platforms, or control with no enrichment. Enrichment resulted in the expression of more behaviours (wing flapping, wing stretching, feather ruffling and foraging), which indicates improved welfare compared to the broilers given no enrichment.
Yildirim and Taskin (2017) tested the effect of 4 enrichment treatments (addition of a perch, ball, mirrors or dust in comparison to broilers with no enrichment. They monitored white blood cell counts and tonic immobility, finding both to be higher in the groups of broilers with no enrichment. The authors concluded that welfare was improved (reduced fear and stress) with the addition of any of the enrichment techniques.
As more research has come out, some attention has turned to the effect of enrichment on cognitive ability. Tahamtani et al. (2018) tested five enrichment treatments (roughage, vertical panels, straw bales and elevated platforms at different heights) in addition to various distances between feeders and waters on fear (tonic immobility) and a learning test to determine ability for learning. Their background explained that in many species, enrichment increases memory and learning, reduces fear and therefore improves welfare. Their results included a reduction in fear when 30 cm platforms were used compared to broilers that had increased distances between feeders and waterers. In addition, birds with straw bales were able to perform better at a passive avoidance test as compared to control broilers, suggesting an improved ability to learn. The authors’ conclusion was that increasing broiler’s environmental complexity improves welfare by reducing fear and improving their ability to learn.
Bach et al. (2019) wanted to study activity levels under various enrichment treatments, as they stated that increased activity in broilers should reduce contact dermatitis and leg issues. Their study aimed to determine if differing types of enrichment could result in different levels and types of active behaviour. Their study tested elevated platforms, either with or without a ramp, vertical panels, straw bales, or maize roughage. They also included different distances between feeders and waterers, and stocking density, compared to an unenriched control treatment. Their results determined that spreading distance between feed and water in the first two weeks increased overall activity. Levels of foraging behaviour increased when maize roughage, but not straw, was included compared to the control group. At days 6 and 27, the reduced stocking density increased locomotion of broilers. More comfort behaviours were performed by broilers given access to platforms, which suggests improved welfare. The authors concluded that various types of enrichment devices can result in different behavioural responses.
Research then moved to determination of style of perches or platforms to use for broilers, as well as the effect on conventional and slow-growing birds. Malchow et al. (2019a) studied 3 levels of perch or platforms (called grids) with a ramp to determine which broilers would use. Their results showed that the platforms were used significantly more than perches. Birds preferred the highest level (50 cm above the floor) of platforms as compared to the 10 or 30 cm platforms, and these were utilized throughout the day and night.
Malchow et al. (2019b) stated once again that enrichment reduces footpad lesions and improves mobility. In their study, these authors compared the use of grids at one of three heights to a control, unenriched treatment, in conventional, medium growing, or slow-growing groups of broilers. The results showed that the slow-growth group preferred the highest grid, while the conventional broiler group utilized the lowest level. The conventional group tended to have better mobility, while the slow-growth group did not show any improvements in the welfare parameters tested. However, all broilers utilized the grid spaces, indicating they had a preference for resting off of the litter.
The amount of grid space may be important in determining how behaviour changes. Baxter et al. (2020) tested 3 grid or perch spaces and a control treatment. Regardless of the treatment, all perch types were utilized by the broilers, with similar amount of time spent on perches. Additionally, birds with perches demonstrated shorter avoidance time compared to broilers in the control treatments (indicating reduced fear), but no differences were noted in vocalizations, latency to approach or play behaviours.
A group from the University of Guelph (Liu et al., 2020) housed 6 pens of broilers in an unenriched environment, and 6 pens in an environment in which there were raised platforms, hanging scales, a pecking stone and a suet feeder filled with wood shavings. The goal was to determine the effect of an enriched environment on play behaviour. The authors used a worm-running ploy to examine the effect of the methodology on spontaneous play behaviour, and found that the broilers in the unenriched environment were more responsive with higher levels of play behaviour. They concluded that these unenriched broilers played more because of their lack of stimulation in their home environment.
Bailie and O’Connell (2014) varied the number of straw bales given to broilers for enrichment, with either 1 bale per 29m2 or 1 per 44m2 of floor space. The increased number of bales had no effect on overall activity of the broilers.
A study by Bergmann et al. (2017) tested enrichment devices with slow growing broilers, including perches and straw bales. In their study, perches were used by d 9. Straw bales provided a sheltered resting space for the broilers, and were later used as pecking objects. The authors concluded that environmental enrichments such as straw bales and perches can stimulate species-specific behaviours, thereby improving animal welfare.
Baxter et al. (2018b) work continued, and in another test, the authors studied the impact on behaviour, in particular dustbathing, when broilers were provided straw bales, oat hulls or straw bales and oat hulls. Behavioural differences were noted, and activity levels increased in all treatments with enrichments compared to an unenriched control treatment. More dustbathing occurred in the oat hull treatment than near the straw bales, but it appeared that birds preferred to rest near the bales. The authors concluded that oat hulls can be a successful enrichment tool for broilers, but that birds do like to rest near bales. It was suggested that if bales were used, an additional treatment of oat hulls would be effective as enrichment tools.
Later research has focused on combinations of enrichment items. Baxter and O’Connell (2019) tested individual enrichment tools or straw bales, oat hulls or pecking chains individually or in combination to understand if combining them would increase activity and improve welfare. In their work, the pecking chain resulted in the highest level of use in the individual groups. Combining the enrichment tools did not increase numbers of birds performing or the type of behaviours performed near the straw bales or oat hull areas. Vertical wingshakes, which suggest positive welfare, occurred more often when oat hulls were presented alone in comparison to when they were grouped with the other enrichment methods. Their conclusions were that there was no advantage to grouping the environmental tools, and that straw bales did not appear to offer protection to the birds.
De Jong and Gunnink (2019) also tested combinations as described above (control group with no enrichments, enriched groups (bales, perches and metal pecking chains) without natural light, or enriched groups with the addition of natural light). Interestingly, groups exposed to enrichment/natural light and control groups were more active than broilers given only enrichment devices (numerically highest in the enrichment/natural light group). No effects were noted in the novel object test (no differences in fear levels). The authors concluded that providing enrichments alone did not increase activity for broilers.
The study previously mentioned, studying the use of a laser light enrichment tool (Meyer et al., 2020) also monitored bird activity, and reported an increase in activity with use of the light. The birds spent more time at the feeder following laser periods than did non-enriched broilers. Their conclusions were that the laser treatment was successful in increasing activity without having a negative effect on mobility.
Poultry are motivated to perform dustbathing activities, and the behaviour also provides the ability to exercise. Baxter et al. (2018a) tested 5 substrates to determine which promoted dustbathing – peat, oat hulls, wood shavings, straw pellets, or litter control. The results indicated that dustbathing activities changed depending on which product was provided, with peat being used the most, and oat hulls the second most used substrate. The least inactivity overall was noted in the peat and oat hull treatments.
Adler et al. (2020), testing broilers growing in houses with partially perforated floors (50% floor space) vs control barns, monitored a number of behavioural parameters. The data showed that birds from the perforated flooring systems were less fearful (d 21 with the avoidance distance test, and the novel object test at d 1, with a tendency for this to occur on d 28).
Pichova et al. (2016) wanted to determine if food-based enrichment could increase foraging in broilers, and in particular, if more enticing food-based enrichment devices would have a larger effect. This group tested 4 groups of broilers – those given meal worms (considered to be highly attractive), whole wheat kernels (medium attractively), wood shavings (not attractive) or no enrichment. Their results indicated that activity and litter scratching were increased significantly when meal worms were provided, but no other differences in activity, nor fear as measured by tonic immobility, were noted.
One study examined outdoor access to enrichment devices. Fanatico et al. (2016) approached the issue of broilers not using range space evenly, and wondered if constructing enrichments that simulated natural structures would increase range usage and alter behaviour in slow-growing Delaware broilers. Their study followed broilers that were housed with pop-holes for outdoor access, and the range space either contained enrichments, or did not contain enrichments. Their study showed that only a small proportion of broilers used the outdoor space regardless of the structure (12.9%). The inclusion of enrichment devices on the outdoor range did encourage broilers to roam further from the house, and the authors concluded that better utilization of outdoor range space occurs when enrichment devices are allowed.
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