Stephanie A F Buijs

Stocking density effects on broiler welfare: Identifying sensitive ranges for different indicators

Although stocking density is perceived as a topic of major importance, no consensus has been reached on what density would allow for good welfare. In the present study, the welfare of 4 replicates of birds stocked at 8, 19, 29, 40, 45, 51, 61, and 72 broilers per pen (or 6, 15, 23, 33, 35, 41, 47, and 56 kg actually achieved BW/m(2)) was studied using 6 welfare indicators. Density did not affect bursa weight, mortality, or concentrations of corticosterone metabolites in droppings but did influence leg health (P = 0.015) and footpad and hock dermatitis (P < 0.001) and tended to influence fearfulness (P = 0.078). However, not every increase in density or group size, or both, led to poorer welfare for the affected indicators: leg health and fearfulness showed unexpected peaks at intermediate densities. Furthermore, the indicators were influenced at different densities: leg strength showed a steep decrease from 6 to 23 kg/m(2), hock dermatitis rose from 35 to 56 kg/m(2), and footpad dermatitis and fearfulness were only significantly higher at the highest density of 56 kg/m(2). No threshold stocking density above which all aspects of welfare were suddenly altered was found in this study. Instead, different aspects of welfare were influenced at different densities or group sizes, or both. Thus, evaluating the effects of stocking density on welfare as a whole would require either identification of acceptable levels for each separate indicator or a weighting of the indicators in an integrated welfare score. A tentative attempt to such an integration, made using equal weights for all parameters, showed a decrease in welfare as density increased (P < 0.001). The lowest 2 densities (6 and 15 kg/m(2)) scored better than most middle densities (23, 33, 35, and 47 kg/m(2)), whereas all densities scored better than the highest density (56 kg/m(2)).

The influence of stocking density on broiler chicken bone quality and fluctuating asymmetry.

Because broiler chickens are juvenile animals undergoing physical development, stocking density during rearing may influence this development. Some of these physical changes may cause welfare problems, for example, decreased bone quality, which may lead to fracture during catching and transport. Others do not influence welfare directly but can be used as indicators of the animals ability to cope with its environment (e.g., fluctuating asymmetry). The present study evaluates the effect of stocking density on bone quality and fluctuating asymmetry. Birds were stocked at densities of 2.4, 5.8, 8.8, 12.1, 13.6, 15.5, 18.5, and 21.8 birds/m(2) from 1 until 39 d of age. Increased stocking density had a negative effect on some aspects of bone quality (tibia curvature and shear strength). Tibias were shorter at high density, possibly due to increased curvature. Several other bone quality aspects (tibia weight, torsion, and dyschondroplasia, and femur curvature and epiphysis shape) remained unaffected. Middle-toe length was the only character that showed a significant increase with increasing density when each character was analyzed separately. Nevertheless, a composite index of fluctuating asymmetry, which combined data on all 11 measured characters, tended to increase with stocking density. Such increased fluctuating asymmetry may indicate decreased welfare. However, one of the assumptions of fluctuating asymmetry is that the animal is subjected to the same environmental influences on both sides. This assumption may not be fulfilled when leg deformations occur, as these may lead to asymmetric changes in bone growth by altering the division of force over the 2 legs. In addition, leg deformations decrease the accuracy of bone length measurements made in a straight line. This raises some concerns on the applicability of fluctuating asymmetry measurements on broiler chicken legs, especially because stocking density did not effect the asymmetry of the head.

Glucocorticoid metabolites in rabbit faeces—Influence of environmental enrichment and cage size

The concentration of glucocorticoid metabolites (GCM) in rabbit faeces has been suggested as a non-invasive indicator of stress. In the present study, GCM concentrations were measured in faeces of fattening rabbits kept in groups of eight, at seven different stocking densities (between 5 and 20 animals/m(2)), with or without environmental enrichment (a wooden structure used mainly for gnawing and resting). Transport (30 min) was used as an acute novel stressor to assess the glucocorticoid response to stress under the different housing conditions. GCM concentrations were elevated post-transport (P<0.001). Whilst cage size had no influence on GCM, enrichment reduced GCM concentrations before as well as after transport (P=0.007 in both cases). Effects of cage size and enrichment on growth characteristics were negligible, whilst enrichment decreased cage manipulation and social contact. The results indicate that even short transport durations may be stressful for rabbits, and that enrichment may decrease housing stress. They suggest that measuring baseline GCM concentrations in faeces is a useful tool to evaluate chronic stress in rabbits, whilst measuring the response to a novel stressor did not provide additional insight.

Cage size and enrichment effects on the bone quality and fluctuating asymmetry of fattening rabbits.

We studied the effect of increased cage size on different aspects of bone quality (bone strength, diameter, weight, and length) and fluctuating asymmetry (FA). Such characteristics may indicate improved animal welfare, as greater bone quality may decrease fracture incidence during handling, whereas decreased FA has been suggested to signal decreased stress. As stress is likely not only influenced by the quantity of space, but also by its quality, we also studied the effect of environmental enrichment. Groups of 8 rabbits were housed in wire open-top cages of 0.40, 0.46, 0.53, 0.64, 0.80, 1.07, and 1.60 m(2) from weaning until slaughter. All cages of 0.40 and 0.46 m(2) (12 cages/size) were left barren to allow sufficient mobility. One-half of the larger cages were enriched with a wooden-enrichment structure that could be used to gnaw on, hide in, or lie in (6 cages per size × enrichment treatment). Increased cage size led to an increase in tibiofibula diameter (P = 0.008), a tendency for increased tibiofibula weight (P = 0.051), and decreased FA (P = 0.010), suggesting improved welfare. Bone length and strength were not affected by cage size (P > 0.1). Enrichment did not affect FA (P > 0.1), in contrast with our expectations based on previous glucocorticoid analysis. This discrepancy between indicators may be due to sensitivity to other types of stressors or different sensitive periods. In summary, rabbits housed in larger cages had wider, heavier bones, but the absence of changes in bone strength indicate that this is unlikely to result in decreased fracture incidence. In larger cages, FA was lower, suggesting a favorable effect on welfare, whereas no effect of enrichment was shown.

Dehydration indicators for broiler chickens at slaughter

Freedom of (prolonged) thirst is considered to be of paramount importance for animal welfare. This emotion normally results from dehydration, which can be measured using physiological indicators. Because no reliable physiological indicator for thirst was available for broilers, we aimed to identify such a measure in this study. This indicator would ideally be integrated into quality control systems in commercial slaughter plants. In the first experiment, water deprivation was manipulated systematically by withdrawing water for different durations (total water withdrawal for 0 (control), 24, 36, or 48 h, or a 10-d period with restricted access to water for 2 times 10 min per day). A significant decrease in drained blood content and BW occurred from 36 h of total water deprivation onward (both P = 0.03), whereas long-term restricted access tended to decrease drained blood content (P = 0.05). No effect of water deprivation or restriction on skin turgor was found. In the second experiment, water was withdrawn for 0 (control), 6, 12, 24, or 48 h. Plasma chloride concentration was increased after 6 h of water withdrawal, but did not rise further with longer withdrawal. If assessed at slaughter, chloride will thus mainly reflect the catching-to-slaughter interval. In contrast, plasma creatinine and hematocrit levels showed a numerical decrease after 6 h of water withdrawal, but rose again after prolonged withdrawal. Plasma creatinine values were significantly higher in 24-h-deprived birds than in 6-h-deprived birds (P < 0.01), allowing for discernment between water withdrawal during catching and transport from dehydration that had occurred on the farm. Blood sodium concentrations and plasma osmolality showed a steady increment between 0 and 24 h of water deprivation (P < 0.001 and P < 0.001 for both), and may thus be used to assess the combined effects of water deprivation on farm and during the catching-to-slaughter interval. These findings may form the basis of an on-farm or at-slaughter test that could be included in integrated animal welfare assessment schemes.

Assessing attraction or avoidance between rabbits: comparison of distance-based methods to analyse spatial distribution

Studies on social spacing usually analyse spatial distribution using a single distribution index, and compare this with expected values assuming random spacing. However, different distribution indices give information on different aspects of spatial distribution. Furthermore, when animals use some parts of the study area more often because of environmental factors, assumptions of random spacing do not apply. As a contribution to the development of spatial distribution analysis methodology, we compared three distribution indices: nearest-neighbour distances (NND), coefficient of variation of interindividual distances and coefficient of variation of Dirichlet polygon areas. Distribution was studied at different animal densities, in the presence or absence of a wooden structure. Rabbits, Oryctolagus cuniculus, were chosen as the model species because of their apparent plasticity of spatial behaviour. The observed distribution was compared with a random distribution and with a resource-corrected random distribution that accounted for environmental influences on spacing. Comparisons with these two distributions led to different conclusions. This emphasizes the limited usefulness of comparisons with the random distribution, especially in more heterogeneous environments. However, divergence from random spacing could potentially be used to assess the relative importance of resources. Especially for 6-week-old rabbits, the density at which no evidence of avoidance was found differed between the distribution indices. This underlines the need to use multiple indices when studying social spacing. Nine-week-old rabbits generally avoided each other’s proximity, with NND indicating proximity avoidance even in the largest pens. Contrary to expectations, the wooden structure seemed to decrease social attraction between rabbits.

Performance of an animal-based test of thirst in commercial broiler chicken farms

Animal-based measures of thirst are currently absent from animal welfare monitoring schemes due to the lack of a well-validated indicator applicable for on-farm use. In the present study, an on-farm test based on voluntary water consumption from an unfamiliar open drinker was validated in a (semi-)commercial setting. To investigate the effect of thirst on water consumption, we subjected 4 flocks of 1,500 broilers to either 0 or 12 h of water deprivation and subsequently measured the amount of water that small subgroups consumed after the deprivation period (first experiment). Broilers that were water deprived before the test drank more than control broilers (P < 0.001). In a second experiment, a similar test was performed using 20 commercial broiler flocks in Belgium and Brazil. After a pretreatment water consumption test, the birds were subjected to 0 or 6 h of water deprivation, and a posttreatment water consumption test was conducted. Only in Brazil, deprived birds drank significantly more than controls in the posttreatment water consumption test (P < 0.001). A tendency for a difference was found in Belgium (P = 0.083). Pre- and posttreatment water consumption was higher in Brazil than in Belgium (P < 0.001). Stocking density and temperature influenced, respectively, the pretreatment and the controls posttreatment water consumption in Brazil, but not in Belgium. These results indicate that the water consumption test is sufficiently sensitive to discriminate between control and 12 h deprived flocks, and in Brazil even between control and 6 h deprived birds. The location of the test within the house did not affect the amount of water consumed in either experiment, suggesting that this variable does not have to be standardized. However, the amount of water consumed by broilers able to drink freely for a long period depended on indoor climatic variables (in Brazil only) and possibly genotype. This suggests that these variables need to be considered when interpreting the test outcome in terms of the thirst level experienced by the broilers.

Behavioural and physiological responses of laying hens to automated monitoring equipment

Highlights • Monitoring devices affected adult hen behaviour on the day of fitting.• Hens prioritized (re)moving newly fitted devices over exploration.• Devices did not increase aggressive behaviour towards equipped hens.• From two days after fitting on, only a very minor effect on behaviour was observed.• Peripheral eye temperature seemed related to preening behaviour rather than stress.