Gina Caplen

Lame broiler chickens respond to non-steroidal anti-inflammatory drugs with objective changes in gait function: A controlled clinical trial

Leg health of intensively reared broiler chickens is a significant problem, yet little is known regarding the nature of lameness-associated pain. Kinematic changes in gait have been reported in naturally lame broilers following subcutaneous non-steroidal anti-inflammatory drug (NSAID) administration, compared to a placebo group. In the current study, an extensive range of gait parameters were defined using a commercial motion-capturing system to record three-dimensional temporospatial information from walking broilers pre- and post-treatment. Data analysis, performed using multi-level models, revealed gait modifications in broilers receiving NSAID, but not in those receiving saline. The effect of walking velocity was accounted for retrospectively. An increase in velocity following NSAID treatment (carprofen: P<0.001; meloxicam: P=0.044) indicated improved walking ability. For several measures, the polarity of the treatment effect depended upon walking speed. At slow speeds certain parameters become more like those of non-lame broilers, which may have been indicative of improved stability: stride length and duration (both NSAIDs), transverse back displacement (meloxicam), and vertical leg displacement (carprofen). However, these same parameters also revealed that NSAID treatment caused imbalance at faster speeds, which may have signified an excessive dosage. Although doses employed were not conclusively effective, evidence was provided that factors besides body conformation influenced mobility in the test cohort. The study showed that the model would be useful in future studies to increase our understanding of pain associated with specific lameness types in broiler chickens.

Kinematic Analysis Quantifies Gait Abnormalities Associated with Lameness in Broiler Chickens and Identifies Evolutionary Gait Differences

This is the first time that gait characteristics of broiler (meat) chickens have been compared with their progenitor, jungle fowl, and the first kinematic study to report a link between broiler gait parameters and defined lameness scores. A commercial motion-capturing system recorded three-dimensional temporospatial information during walking. The hypothesis was that the gait characteristics of non-lame broilers (n = 10) would be intermediate to those of lame broilers (n = 12) and jungle fowl (n = 10, tested at two ages: immature and adult). Data analysed using multi-level models, to define an extensive range of baseline gait parameters, revealed inter-group similarities and differences. Natural selection is likely to have made jungle fowl walking gait highly efficient. Modern broiler chickens possess an unbalanced body conformation due to intense genetic selection for additional breast muscle (pectoral hypertrophy) and whole body mass. Together with rapid growth, this promotes compensatory gait adaptations to minimise energy expenditure and triggers high lameness prevalence within commercial flocks; lameness creating further disruption to the gait cycle and being an important welfare issue. Clear differences were observed between the two lines (short stance phase, little double-support, low leg lift, and little back displacement in adult jungle fowl; much double-support, high leg lift, and substantial vertical back movement in sound broilers) presumably related to mass and body conformation. Similarities included stride length and duration. Additional modifications were also identified in lame broilers (short stride length and duration, substantial lateral back movement, reduced velocity) presumably linked to musculo-skeletal abnormalities. Reduced walking velocity suggests an attempt to minimise skeletal stress and/or discomfort, while a shorter stride length and time, together with longer stance and double-support phases, are associated with instability. We envisage a key future role for this highly quantitative methodology in pain assessment (associated with broiler lameness) including experimental examination of therapeutic agent efficacy.

Consistency, transitivity and inter-relationships between measures of choice in environmental preference tests with chickens

Choice experiments are a widespread method of assessing the welfare requirements of domestic animals but prior predictions about what animals should choose to maximise their welfare are not possible. It is therefore important to analyse the data from sets of choice tests to establish whether intra-set and inter-set consistency in choice occurs. Strong inter-set consistency (transitivity) would provide support for the assumption that animals are maximising a complex utility (welfare) that may map onto their subjective state. We housed 56 hens Gallus gallus sequentially in three environments, experienced as three sets (A vs B; B vs C; A vs C), over a 40-week period. At the end of each set, each chicken made six choices between the items in that set, using T-maze testing procedures. The chickens showed significantly greater within-set consistency than expected by chance (p<0.001 for all sets). Although different chickens exhibited different environmental preferences, we also found that a high within-set consistency was associated with faster decision-making (p<0.001). When the three sets of choice trials for each hen were compared there was some evidence that the birds made more transitive choices (indicating consistent choices between sets) than expected by chance.

Thermal nociception as a measure of non-steroidal anti-inflammatory drug effectiveness in broiler chickens with articular pain

Pain associated with poultry lameness is poorly understood. The anti-nociceptive properties of two non-steroidal anti-inflammatory drugs (NSAIDs) were evaluated using threshold testing in combination with an acute inflammatory arthropathy model. Broilers were tested in six groups (n = 8 per group). Each group underwent a treatment (saline, meloxicam (3 or 5 mg/kg) or carprofen (15 or 25 mg/kg)) and a procedure (Induced (arthropathy-induction) or sham (sham-handling)) prior to testing. Induced groups had Freund’s complete adjuvant injected intra-articularly into the left intertarsal joint (hock). A ramped thermal stimulus (1 °C/s) was applied to the skin of the left metatarsal. Data were analysed using random-intercept multi-level models. Saline-induced birds had a significantly higher skin temperature (± SD) than saline-sham birds (37.6 ± 0.8 °C vs. 36.5 ± 0.5 °C; Z = −3.47, P < 0.001), consistent with an inflammatory response. Saline was associated with significantly lower thermal thresholds (TT) than analgesic treatment (meloxicam: Z = 2.72, P = 0.007; carprofen: Z = 2.58, P = 0.010) in induced birds. Saline-induced birds also had significantly lower TT than saline-sham birds (Z = −2.17, P = 0.030). This study found direct evidence of an association between inflammatory arthropathies and thermal hyperalgesia, and showed that NSAID treatment maintained baseline thermal sensitivity (via anti-nociception). Quantification of nociceptive responsiveness in a predictable broiler pain model identified thermal anti-hyperalgesic properties of two NSAIDs, which suggested that therapeutically effective treatment was provided at the doses administered. Such validation of analgesic strategies will increase the understanding of pain associated with specific natural broiler lameness types.

Lameness is consistently better at predicting broiler chicken performance in mobility tests than other broiler characteristics

To determine whether lame broilers are in pain it is necessary to compare measures of lameness and mobility before and after analgesic treatment. Such measures should not be unduly affected by other bird characteristics. This study assessed the performance of lame (gait score, GS 3–4) and non-lame (GS 0–1) broilers using two mobility tests: (i) a novel test to assess broiler ability to access resources when housed in groups (Group Obstacle test); and (ii) a Latency-to-Lie (LTL) test. Outcome test measures included number of obstacle crossings, latency to cross an obstacle, and time taken to sit in shallow water. Associations between outcome test measures and other bird characteristics (established lameness risk-factors), including strain, sex, age, mass, contact dermatitis and pathology, were also investigated. The performance of high-GS and low-GS broilers differed in both mobility tests and no other bird characteristics were as consistent a predictor as lameness. This demonstrates that mobility impairments are closely related to lameness assessed using GS, and that there is a component of lameness that cannot be explained by other bird characteristics (eg being male and heavy). This component may represent pain or discomfort. Both mobility tests are suitable for further application with analgesic testing to classify lameness-associated pain in broilers.

Thermal nociceptive threshold testing detects altered sensory processing in broiler chickens with spontaneous lameness

Lameness is common in commercially reared broiler chickens but relationships between lameness and pain (and thus bird welfare) have proved complex, partly because lameness is often partially confounded with factors such as bodyweight, sex and pathology. Thermal nociceptive threshold (TNT) testing explores the neural processing of noxious stimuli, and so can contribute to our understanding of pain. Using an acute model of experimentally induced articular pain, we recently demonstrated that TNT was reduced in lame broiler chickens, and was subsequently attenuated by administration of Non-Steroidal Anti-Inflammatory Drugs (NSAIDs). This study extended these findings to a large sample of commercial broilers. It examined factors affecting thermal threshold (Part 1) and the effect of an NSAID drug (meloxicam, 5 mg/kg) and of an opioid (butorphanol; 4 mg/kg) (Part 2). Spontaneously lame and matched non-lame birds (n = 167) from commercial farms were exposed to ramped thermal stimulations via a probe attached to the lateral aspect of the tarsometatarsus. Baseline skin temperature and temperature at which a behavioural avoidance response occurred (threshold) were recorded. In Part 1 bird characteristics influencing threshold were modelled; In Part 2 the effect of subcutaneous administration of meloxicam or butorphanol was investigated. Unexpectedly, after accounting for other influences, lameness increased threshold significantly (Part 1). In Part 2, meloxicam affected threshold differentially: it increased further in lame birds and decreased in non-lame birds. No effect of butorphanol was detected. Baseline skin temperature was also consistently a significant predictor of threshold. Overall, lameness significantly influenced threshold after other bird characteristics were taken into account. This, and a differential effect of meloxicam on lame birds, suggests that nociceptive processing may be altered in lame birds, though mechanisms for this require further investigation.

Effects of carprofen, meloxicam and butorphanol on broiler chickens’ performance in mobility tests

Lame broiler chickens perform poorly in standardised mobility tests and have nociceptive thresholds that differ from those of nonlame birds, even when confounding factors such as differences in bodyweight are accounted for. This study investigated whether these altered responses could be due to pain, by comparing performance in a Group Obstacle test and a Latency to Lie (LTL) test of lame (Gait Score [GS] 2.5–4) and non-lame (GS 0–1) broilers administered analgesia or a saline control. We used exploratory subcutaneous doses of the non-steroidal anti-inflammatory drugs (NSAIDs), meloxicam (5 mg kg) or carprofen (35 mg kg) or the opioid butorphanol tartrate (4 mg kg). We included butorphanol to explore the possibility that NSAIDs could improve mobility by reducing inflammation without necessarily invoking an analgesic effect. Lameness was a significant predictor in all analyses. Neither the number of obstacle crossings nor latency to cross an obstacle was significantly changed by either NSAID, but LTL was longer in lame birds given carprofen and meloxicam than in lame birds given saline. LTL was associated with foot-pad dermatitis and ameliorated by both NSAIDs. Butorphanol did not affect LTL but appeared soporific in the obstacle test, increasing latency to cross and, in non-lame birds, reducing the number of crossings. Combined with data from other studies, the results suggest carprofen and meloxicam had some analgesic effect on lame birds, lending further support to concerns that lameness compromises broiler welfare. Further investigation of opioid treatments and lameness types is needed to disentangle effects on mobility and on pain.

Examining affective structure in chickens: valence, intensity, persistence and generalization measured using a Conditioned Place Preference Test

Highlights • Conditioned Place Preference tests were used to study affective responses in hens.• Both air puff and water spray stimuli produced conditioned place aversions.• A robotic snake, and the sound of conspecific alarm calls, did not.• Negative affective responses can differ in their persistence and generalization.