Are changes in behavior of fast-growing broilers with slight gait impairment (GS0-2) related to pain?

On-farm study of walking ability in conventional broilers and those labelled as being higher welfare

BACKGROUND

Multiple factors, including genetics and management practices, are known to influence the walking ability of broilers. This field survey aimed to assess the walking ability of broilers in two different production systems.

METHODS

Thirty flocks of conventional (Ross 308) and 26 flocks of welfare-labelled (Level 1; Ranger Gold/Rustic Gold) broilers were evaluated, with maximum stocking densities of 40 and 38/38 kg/m2 and growth rates of 62-63 g/day and 43-45/47-51 g/day, respectively. Gait scores were obtained for approximately 120 birds/flock prior to slaughter using the six-point Bristol scale, with scores ranging from 0 (no detectable abnormality) to 5 (complete lameness). Data on broiler age, target bodyweight on day of assessment and genotype were collected.

RESULTS

The odds of birds having gait scores greater than 0 (p = 0.011), 1 (p < 0.001) and 2 (p = 0.033) increased significantly with a 100 g increase in bodyweight for conventional broilers, whereas no such effect was found for level 1 broilers. Within the level 1 system, the slower-growing Ranger Gold birds had lower odds of having gait scores greater than 1 than the faster-growing Rustic Gold birds (p = 0.022).

LIMITATIONS

Data on the bodyweight of individual birds were not collected.

CONCLUSION

The results obtained in this study are in line with previous research showing that walking ability is negatively associated with growth rate.

Feeding behaviour patterns in relation to body weight and gait in broilers

Collecting data on broiler behaviour patterns in group-housed settings can be challenging, as broilers are difficult to recognize individually. However, broiler behaviour patterns can be valuable for assessing health, welfare and performance. Here, individual feeding patterns of group-housed broilers were studied. Data on feeder visits of 58 randomly selected and subsequently RFID-tagged broilers were used, that were housed in a group of approximately 800 birds in a 45 m2 pen. Feed and water were provided ad libitum, with a total of 16 feeders available to the broilers. All feeders except one (due to farm equipment blocking the access) were fitted with an RFID antenna to detect presence of the broilers at the feeders. The number of feeder visits and feeding durations at the individual level during the period from 20 to 30 d old were examined. In addition, birds' individual body weights (g) were determined at 14, 21, 27 and 35 d of age, and at 21, 27 and 35 d of age gait scores were determined by experienced observers. The feeders used within the pen (i.e., whether feeding occurred in one area or was spread out across the pen) varied between individuals, and for some birds also changed with age. Furthermore, with higher body weights at 14 d of age, the number of different feeders visited in a day was lower (estimate = -0.011, P = 0.002) and the mean feeding bout duration was higher (estimate = 0.130, P = 0.007). In contrast, larger body weight gain between 14 and 35 d of age was related to more different feeders visited within a day (estimate = 0.028, P = 0.005) and shorter feeding bout durations (estimate = -0.390, P = 0.005). No relationships of feeding descriptors with gait classification were observed. Overall, feeding patterns vary between individual broilers and, given the observed relationships between feeding patterns and weight gain, feeding patterns have potential to be informative for broiler growth in research and commercial conditions.

Top-view characterization of broiler walking ability and leg health using computer vision

Impaired walking ability and leg health are commonly seen in broilers and can negatively impact their welfare. Commonly, walking ability and leg health are assessed manually, but this is time consuming and can be subjective. Automated approaches for scoring walking ability and leg health at the individual level could therefore have great added value. Here, we studied whether automatically extracted top-view walking features of broilers can be used as a proxy for walking ability and leg health. Top-view videos were collected of unmarked broilers walking through a corridor that was placed inside the home pen. From these videos, four top-view features were derived: 1) lateral body oscillation, calculated as deviations from the movement trajectory of the bird, 2) step count, 3) completion time, and 4) length-width ratio of the virtual bounding box encapsulating the bird while walking as an indicator of wing support. We assessed the relationship of these computer vision-based features with manual gait and leg health scores, including hock burn (HB) and footpad dermatitis (FPD). We observed that birds with worse gait scores (GS) had longer completion times, higher step counts and a trend for higher lateral body oscillation levels in the walkway setup. Unsupervised clustering using the K-means algorithm with these walking features showed potential to distinguish birds with GS3+, although differentiating between GS1 and GS2 proved more challenging. We concluded that the length-width ratio of the bounding box during walking was not a suitable proxy for poor gait. We found no relationship between top-view walking features and mild cases of HB and FPD in broilers. Overall, the results of this study indicate that top-view video recordings can provide insight into birds' walking ability, using features related to movement speed, step count and lateral body oscillation, making automated scoring more feasible on a larger scale in practice. However, these top view features provide little information about mild HB and FPD.

Research Note: Testing the validity of latency-to-lie tests without water for objective on-farm assessment of walking ability of broiler chickens

The latency-to-lie (LTL) test is an objective method for assessing walking ability of broiler chickens which has traditionally consisted of placing a bird into a tub of shallow water and measuring how long it takes the standing bird to sit, with duration being negatively associated with gait score. Unfortunately, this method is impractical for use on commercial farms. Thus, the aim of this study was to assess the performance of LTL tests without the addition of water, making them more practical for use on farm. In total, 159 Ross 308 and 186 Rustic Gold broilers were assessed. Following receiving a gait score (Bristol scale), birds were placed individually into a litter lined clear plastic storage box and the LTL was conducted with a maximum test duration of 300 s. Following a 120 s period of rest, the bird was then placed on the litter near a group of flockmates, and the LTL test was repeated. This allowed for the assessment of whether containment of the bird was necessary. Latencies to lie were negatively correlated with gait score (With box: ρ=-0.44 , P < 0.001; Without box: ρ=-0.46 , P < 0.001). The latencies to lie (mean ± SD) when using a box were 129.0 ± 82.0, 114.0 ± 78.8, 71.9 ± 54.9, 45.8 ± 35.8, and 7.9 ± 14.0 s and without a box were 104.0 ± 97.2, 52.2 ± 53.8, 27.9 ± 29.9, 22.8 ± 27.0, and 14.0 ± 19.4 s for gait scores 0, 1, 2, 3, and 4, respectively. There was no effect of hybrid on the performance of either of the tests. Results suggest that the LTL tests without water could serve as an objective and valid measure of walking ability on farm, with the LTL test with a box showing better ability at distinguishing between specific gait scores compared to the LTL test without a box, though possible impacts of fatigue due to study design should be considered.

Impact of Growth Rate on the Welfare of Broilers

Selection for the more efficient production of broilers has resulted in rapid growth rates. The aim was to review the existing knowledge on the effect of growth rate on broiler welfare. Genotypes with faster growth rates consistently demonstrate poorer gait scores and increased prevalence of disorders affecting their legs than slower-growing genotypes. Reduced mobility places faster-growing broilers at an increased risk of developing contact dermatitis, as they spend increased durations sitting in contact with litter. Poor walking ability, heavy body weights, and conformational differences such as proportionally larger breast muscle in genotypes with faster growth can impact a bird's ability to walk and navigate the environment, making it difficult to access resources and express natural behaviors. Faster growth has also been associated with poor cardiovascular health, increased susceptibility to heat stress, increased prevalence of mortality, ascites, as well as multiple breast muscle myopathies. Feed restriction, a practice associated with hunger and frustration, may be used to control the growth of broiler breeders, with birds having higher growth potential typically experiencing higher restriction levels. Overall, there is strong evidence that fast growth rates negatively impact welfare, and that slower-growing genotypes show significantly improved welfare. Furthermore, some evidence suggests that even minor reductions in growth rate can lead to welfare improvements.

Overview of the various methods used to assess walking ability in broiler chickens

BACKGROUND

Walking ability is a highly important animal-based indicator of welfare in broilers that warrants monitoring across commercial production.

METHODS

A review of the technical and scientific literature on existing methods for assessing walking ability in broilers was conducted, and the reliability, validity and feasibility of the different methods were assessed when relevant information was available.

RESULTS

Visual gait scoring has high validity, minimal equipment needs and is relatively quick to perform; however, this method is subjective and requires extensive training. Due to this, more objective tests, such as the latency to lie test, have been developed, although more validation of these tests is required. Other identified methods, such as obstacle courses, the rotarod test and kinetic and kinematic approaches, require considerable amounts of equipment, making them impractical for use during on-farm inspections. Automated methods that rely on movement or activity data have potential for future development but currently lack the resolution of traditional gait scoring and require equipment such as cameras or accelerometers.

CONCLUSIONS

Objective, seemingly valid, repeatable and feasible options exist for the assessment of walking ability that would facilitate the monitoring of commercial broiler welfare; however, more validation of these methods is required, especially in commercial farm settings.

Environmental complexity impacts anxiety in broiler chickens depending on genetic strain and body weight

The objective was to assess the impact of environmental complexity on affective state (anxiety) in fast- and slow-growing broilers (Gallus gallus domesticus) as they gain weight. Six hundred fast-growing broilers (Ross 708; "fast-growers") and 600 slow-growing broilers (Hubbard Redbro Mini; "slow-growers") were raised in 24 pens with simple (standard; SE) or complex (permanent and temporary enrichments; CE) environments. Six birds/pen underwent the attention bias test on day 23 (fast-growers only), 28-29, 35-36, 42-43, and 56-57 (slow-growers only), with individuals only tested once (n = 576). Proportion of birds feeding, time spent vigilant and latencies to eat and step were recorded. Greater vigilance and longer latencies indicate more anxiety. Slow-growers fed more (p = 0.001), were less vigilant (p = 0.003), and stepped sooner than fast-growers (p = 0.007). For both strains, likelihood of feeding was unrelated to weight in SE, but decreased with increasing weight in CE (p = 0.048). Birds in CE stepped sooner than birds in SE (p = 0.030). Vigilance increased with body weight (p = 0.024). These results indicate that affective state (anxiety) can change as birds gain weight, depending on environmental complexity and genetic strain. Overall, slow-growers showed reduced anxiety compared to fast-growers, across housing treatments or weights.

Classification of Behaviour in Conventional and Slow-Growing Strains of Broiler Chickens Using Tri-Axial Accelerometers

Behavioural states such as walking, sitting and standing are important in indicating welfare, including lameness in broiler chickens. However, manual behavioural observations of individuals are often limited by time constraints and small sample sizes. Three-dimensional accelerometers have the potential to collect information on animal behaviour. We applied a random forest algorithm to process accelerometer data from broiler chickens. Data from three broiler strains at a range of ages (from 25 to 49 days old) were used to train and test the algorithm, and unlike other studies, the algorithm was further tested on an unseen broiler strain. When tested on unseen birds from the three training broiler strains, the random forest model classified behaviours with very good accuracy (92%) and specificity (94%) and good sensitivity (88%) and precision (88%). With the new, unseen strain, the model classified behaviours with very good accuracy (94%), sensitivity (91%), specificity (96%) and precision (91%). We therefore successfully used a random forest model to automatically detect three broiler behaviours across four different strains and different ages using accelerometers. These findings demonstrated that accelerometers can be used to automatically record behaviours to supplement biomechanical and behavioural research and support in the reduction principle of the 3Rs.

Automated pose estimation reveals walking characteristics associated with lameness in broilers

Walking ability of broilers can be improved by selective breeding, but large-scale phenotypic records are required. Currently, gait of individual broilers is scored by trained experts, however, precision phenotyping tools could offer a more objective and high-throughput alternative. We studied whether specific walking characteristics determined through pose estimation are linked to gait in broilers. We filmed male broilers from behind, walking through a 3 m × 0.4 m (length × width) corridor one by one, at 3 time points during their lifetime (at 14, 21, and 33 d of age). We used a deep learning model, developed in DeepLabCut, to detect and track 8 keypoints (head, neck, left and right knees, hocks, and feet) of broilers in the recorded videos. Using the keypoints of the legs, 6 pose features were quantified during the double support phase of walking, and 1 pose feature was quantified during steps, at maximum leg lift. Gait was scored on a scale from 0 to 5 by 4 experts, using the videos recorded on d 33, and the broilers were further classified as having either good gait (mean gait score ≤2) or suboptimal gait (mean gait score >2). The relationship of pose features on d 33 with gait was analyzed using the data of 84 broilers (good gait: 57.1%, suboptimal gait: 42.9%). Birds with suboptimal gait had sharper hock joint lateral angles and lower hock-feet distance ratios during double support on d 33, on average. During steps, relative step height was lower in birds with suboptimal gait. Step height and hock-feet distance ratio showed the largest mean deviations in broilers with suboptimal gait compared to those with good gait. We demonstrate that pose estimation can be used to assess walking characteristics during a large part of the productive life of broilers, and to phenotype and monitor broiler gait. These insights can be used to understand differences in the walking patterns of lame broilers, and to build more sophisticated gait prediction models.

Welfare of broilers on farm

This Scientific Opinion considers the welfare of domestic fowl (Gallus gallus) related to the production of meat (broilers) and includes the keeping of day-old chicks, broiler breeders, and broiler chickens. Currently used husbandry systems in the EU are described. Overall, 19 highly relevant welfare consequences (WCs) were identified based on severity, duration and frequency of occurrence: 'bone lesions', 'cold stress', 'gastro-enteric disorders', 'group stress', 'handling stress', 'heat stress', 'isolation stress', 'inability to perform comfort behaviour', 'inability to perform exploratory or foraging behaviour', 'inability to avoid unwanted sexual behaviour', 'locomotory disorders', 'prolonged hunger', 'prolonged thirst', 'predation stress', 'restriction of movement', 'resting problems', 'sensory under- and overstimulation', 'soft tissue and integument damage' and 'umbilical disorders'. These WCs and their animal-based measures (ABMs) that can identify them are described in detail. A variety of hazards related to the different husbandry systems were identified as well as ABMs for assessing the different WCs. Measures to prevent or correct the hazards and/or mitigate each of the WCs are listed. Recommendations are provided on quantitative or qualitative criteria to answer specific questions on the welfare of broilers and related to genetic selection, temperature, feed and water restriction, use of cages, light, air quality and mutilations in breeders such as beak trimming, de-toeing and comb dubbing. In addition, minimal requirements (e.g. stocking density, group size, nests, provision of litter, perches and platforms, drinkers and feeders, of covered veranda and outdoor range) for an enclosure for keeping broiler chickens (fast-growing, slower-growing and broiler breeders) are recommended. Finally, 'total mortality', 'wounds', 'carcass condemnation' and 'footpad dermatitis' are proposed as indicators for monitoring at slaughter the welfare of broilers on-farm.

Enhancing their quality of life: environmental enrichment for poultry

Providing environmental enrichments that increase environmental complexity can benefit poultry welfare. This Poultry Science Association symposium paper is structured around four themes on 1) poultry preferences and affective states 2) species-specific behavior, including play behavior and the relationship between behavior, activity level and walking ability, 3) environmental enrichment and its relationship with indicators of welfare, and 4) a case study focusing on the application of enrichments in commercial broiler chicken production. For effective enrichment strategies, the birds' perspective matters most, and we need to consider individual variation, social dynamics, and previous experience when assessing these strategies. Play behavior can be a valuable indicator of positive affect, and while we do not yet know how much play would be optimal, absence of play suggests a welfare deficit. Activity levels and behavior can be improved by environmental modifications and prior research has shown that the activity level of broilers can be increased, at least temporarily, by increasing the environmental complexity. However, more research on impacts of enrichments on birds' resilience, on birds in commercial conditions, and on slow(er)-growing strains is needed. Finally, incorporating farmers' expertise can greatly benefit enrichment design and implementation on commercial farms.

Behaviour in Slower-Growing Broilers and Free-Range Access on Organic Farms in Sweden

Two slower-growing hybrids (Rowan Ranger and Hubbard) are currently reared in organic broiler production in Sweden, but knowledge of bird welfare on commercial farms is limited. This study examined chicken behaviour, including free-range use and features of this, in order to enhance knowledge, describe the current situation and identify practical solutions on Swedish organic broiler farms. Eight of 12 available farms were visited once each, when average flock age was 55 ± 6 days. Farmer interviews were followed by avoidance distance tests, group behavioural observations, and assessment of use of environmental enrichment and free-range by the chickens. On average, almost half of all birds observed indoors were in a sitting posture. However, even when approaching slaughter age, the chickens were agile enough to perch and used some of the variety of items provided for perching, but the quantity of environmental enrichment equipment appeared to be insufficient. Free-range areas generally lacked sufficient vegetation cover or artificial shelters, and chickens were predominantly observed ranging near the house. Further research should explore feasible ways for farmers to make key improvements to the indoor and outdoor environment, in order to improve broiler welfare.

Post-mortem examination of fast-growing broilers with different degrees of identifiable gait defects

BACKGROUND

The walking ability of many broilers is characterised by slight or definite defects categorised as gait scores (GS) 1 and 2. The present study aimed to examine potential relationships between GSs and indicators of body morphology, leg pathology, tibia strength and wooden breast in Ross 308 broilers assessed as GS ≤ 2.

METHODS

At 38 days of age, GS and live body weight of 179 birds was recorded. Each bird was examined post-mortem for signs of wooden breast, contact dermatitis and a range of leg pathologies. Weights of different body parts and tibia strength were quantified.

RESULTS

Within sex, GS increased with increasing live body weight (p = 0.020). There was a tendency for an effect of GS on prevalence of footpad dermatitis (p = 0.086) and dislocated femoral joint cartilage (p = 0.059) where both pathologies increased in frequency with increasing GS. Greater load was required to fracture tibia from GS2 than GS0 birds (p = 0.040).

CONCLUSIONS

Within this relatively small data set, no strong relationships between GS ≤ 2 and indicators of body morphology, leg pathology, tibia strength and wooden breast in Ross 308 broilers were found, except for the live terminal body weight. Further studies, involving larger data sets are required for full clarification.