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.

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

Impaired walking ability in terms of slight or definite defects is more common in broiler production than lameness that obviously hinders movement, but it has received limited scientific attention. This study aimed to compare behavior of conventional broilers with impaired walking ability (assessed as gait score (GS) 2) with those walking normally (GS0) and those with only a slight gait defect (GS1). Behavior in the home environment was registered, and an analgesic intervention to quantify changes in time budgets indicating pain relief was applied. The study included 192 Ross 308 broilers. On day 27 of age, the birds were distributed as evenly as possible into birds of GS0 and GS2 of each sex based on obtained gait score. Following this, each experimental bird was housed with 3 companion birds. On days 30 and 32 of age, the behavior in the home pens was recorded. All experimental birds were injected with the NSAID carprofen on one of the 2 d and saline on the other. The statistical analyses used the GS scored on the day of recording as explanatory factor. Compared to GS0 birds, GS2 birds tended to be more inactive (mean (CI): 4,193 (3,971-4416) vs. 4,005 (3,753-4,257) s; P = 0.074), spent more time sitting while feeding (306 (266-353) vs. 213 (180-251) s; P = 0.026), were less likely to perch (probability: 0.78 (0.69-0.85) vs. 0.91 (0.85-0.95); P = 0.012), and spent less time performing comfort behavior (749 (689-814) s vs. 875 (792-967) s; P = 0.043). Compared to GS1 birds, GS2 birds spent more time inactive (GS1: 4,022 (3,818-4225) s; P = 0.027), less time foraging (289 (253-329) vs. 347 (309-388) s; P = 0.047), and were less likely to perch (GS1: 0.90 (0.86-0.93); P = 0.001). For some of these behavioral variables, administration of carprofen led to behavioral changes across the GSs, which may suggest that the behavioral expression of the broilers was limited by pain. These findings are of relevance to animal welfare, but the underlying causes are still not fully clarified.

A High Enrichment Replenishment Rate Reduces Damaging Behaviors and Increases Growth Rate in Undocked Pigs Kept in Fully Slatted Pens.

One of the difficulties in complying with the prohibition of routine tail docking is a lack of effective alternative solutions to prevent tail biting, especially in fully slatted systems. This study compared three slat-compatible enrichment replenishment strategies for pigs. Forty-eight mixed-sex pens (six males and six females/pen) of undocked pigs were followed from birth to slaughter. Pre-weaning, half the pigs were provided with enrichment materials (a cardboard cup, rubber toy, hessian cloth and bamboo), in addition to a rope for the sows, in all farrowing crates. Post-weaning, all pens were enriched with eight identical items, including an elevated rack supplied with fresh-cut grass, and objects of wooden, bamboo, rubber, and fabric materials presented in various ways. However, three different replenishment frequencies were applied: "Low" (replenished on Monday/Wednesday/Friday), "Medium" (replenished once daily), and "High" (replenished ad libitum). Individual pigs were weighed on days 0, 49, 91, and 113 post-weaning. Direct behavior observations were conducted twice weekly at pen level (10 min/day/pen), and tail and ear lesion scores of individual pigs were also recorded every other week. These measurements were taken during the post-weaning period. The cost of all enrichment materials used was calculated. Pre-weaning enrichment only contributed to a lower ear lesion score (P = 0.04). No difference in lesion scores was found between post-weaning treatments. "Low" replenishment rate pigs performed more damaging behaviors (tail/ear biting, belly-nosing, mounting, other biting, and aggressive behaviors combined) than "High" and "Medium" pigs (P < 0.01). The average daily gain in the finishing stage was higher in "High" than "Low" pigs (P < 0.05). Although sporadic tail biting occurred, only 0.69% of the pigs had their tails bitten severely enough that they became shorter than half of a normal undocked tail. The average enrichment cost for the post-weaning period was <€2 per pig. In conclusion, the high enrichment replenishment rate increased growth and reduced damaging behaviors compared to the low replenishment rate pigs. Overall, these findings show that the provision and regular replenishment of multiple, slat-compatible, enrichment sources can reduce tail damage to manageable levels without the need for tail docking.

Can increased dietary fibre level and a single enrichment device reduce the risk of tail biting in undocked growing-finishing pigs in fully slatted systems?

This study evaluated the effectiveness of combined dietary and enrichment strategies to manage tail biting in pigs with intact tails in a conventional fully-slatted floor housing system. A 2 × 2 × 2 factorial design was used. Pigs had either a high fibre (weaner 5.3% and finisher 11.6% of crude fibre) or standard fibre diet (weaner 3.7% and finisher 5.9% of crude fibre). In the weaner stage, pigs had either a spruce wooden post (supplied in a wall-mounted dispenser) or a rubber floor toy as a enrichment device, and in the finisher stage, they had either the same or alternate enrichment item. Six hundred and seventy-two pigs were assigned to 48 pens of 14 pigs and followed from weaning until slaughter. Individual tail lesion scores and pen level behaviours were directly recorded every 2 weeks. Twenty-six pens had tail biting outbreaks and 161 injured pigs needed removal for treatment. Pigs fed with the high fibre diet performed more tail biting (p < 0.05) and tended to have a worse tail damage scores than those fed the standard fibre diet (p = 0.08). Pigs which had the floor toy as weaners and wood as finishers tended to have fewer tail lesions in the finisher stage than their counterparts (p = 0.06). Pigs receiving the floor toy as enrichment interacted with the enrichment more frequently overall (p < 0.001) and performed fewer harmful behaviours in the weaner stage (p < 0.05). Overall, higher fibre in the diet in a relatively barren environment did not help reduce tail biting or tail lesions. Altering the fibre level in the pigs' diet and providing a single enrichment device to undocked pigs on fully slatted floors resulted in a high level of tail biting and a large proportion of pigs with partial tail amputation.

The Effect of LPS and Ketoprofen on Cytokines, Brain Monoamines, and Social Behavior in Group-Housed Pigs.

Poor health is a risk factor for damaging behaviors, but the mechanisms behind this link are unknown. Injection of pigs with lipopolysaccharide (LPS) can be used to model aspects of poor health. Recent studies have shown that LPS-injected pigs perform more tail- and ear-directed behavior compared to saline-injected pigs and suggest that pro-inflammatory cytokines may play a role in these behaviors. The aims of this study were to test the effect of LPS on the social behavior of pigs and the neurotransmitters and modulators in their brains and to test the effect of a nonsteroidal anti-inflammatory drug on the effects of LPS. Fifty-two female pigs (11-12 weeks) were allocated to four treatments comprising two injections: saline-saline (SS), saline-LPS (SL), ketoprofen-saline (KS), and ketoprofen-LPS (KL). Activity was scan-sampled every 5 min for 6 h after the last injection in the pen. Social behavior was observed continuously in 10 × 15-min bouts between 8 a.m. and 5 p.m. 1 day before (baseline) and 1 and 2 days after the injection. Saliva was analyzed for cortisol and plasma for tryptophan and kynurenine. The frontal cortex, hippocampus, hypothalamus, and brain stem were sampled 72 h after the injection and analyzed for cytokines and monoamines. LPS activated the HPA axis and decreased the activity within 6 h after the injection. Ketoprofen lowered the effect of LPS on cortisol release and attenuated the behavioral signs of sickness in challenged pigs. SL pigs manipulated the ears of their pen mates significantly longer than SS pigs 2 days after the injection. LPS had no observed effect on IFN-γ, TNF-α, and IL-18. At 72 h after the injection, plasma tryptophan was depleted in SL pigs, and tryptophan and kynurenine concentrations in the frontal cortex and brain stem of SL pigs were significantly lower compared to those in SS pigs. Dopamine concentrations in the hypothalamus of SL pigs were significantly lower compared to those in SS pigs. Serotonin concentrations in the hypothalamus and noradrenaline concentrations in the hippocampus of SL pigs were significantly lower compared to those in KL pigs. In conclusion, LPS influenced the different neurotransmitters and modulators in the brain that are hypothesized to play an important role in the regulation of mood and behavior.

Transcriptomics Analysis of Porcine Caudal Dorsal Root Ganglia in Tail Amputated Pigs Shows Long-Term Effects on Many Pain-Associated Genes.

Tail amputation by tail docking or as an extreme consequence of tail biting in commercial pig production potentially has serious implications for animal welfare. Tail amputation causes peripheral nerve injury that might be associated with lasting chronic pain. The aim of this study was to investigate the short- and long-term effects of tail amputation in pigs on caudal DRG gene expression at different stages of development, particularly in relation to genes associated with nociception and pain. Microarrays were used to analyse whole DRG transcriptomes from tail amputated and sham-treated pigs 1, 8, and 16 weeks following tail treatment at either 3 or 63 days of age (8 pigs/treatment/age/time after treatment; n = 96). Tail amputation induced marked changes in gene expression (up and down) compared to sham-treated intact controls for all treatment ages and time points after tail treatment. Sustained changes in gene expression in tail amputated pigs were still evident 4 months after tail injury. Gene correlation network analysis revealed two co-expression clusters associated with amputation: Cluster A (759 down-regulated) and Cluster B (273 up-regulated) genes. Gene ontology (GO) enrichment analysis identified 124 genes in Cluster A and 61 genes in Cluster B associated with both "inflammatory pain" and "neuropathic pain." In Cluster A, gene family members of ion channels e.g., voltage-gated potassium channels (VGPC) and receptors e.g., GABA receptors, were significantly down-regulated compared to shams, both of which are linked to increased peripheral nerve excitability after axotomy. Up-regulated gene families in Cluster B were linked to transcriptional regulation, inflammation, tissue remodeling, and regulatory neuropeptide activity. These findings, demonstrate that tail amputation causes sustained transcriptomic expression changes in caudal DRG cells involved in inflammatory and neuropathic pain pathways.

Multi-Step Tail Biting Outbreak Intervention Protocols for Pigs Housed on Slatted Floors.

Solutions are needed to keep pigs under commercial conditions without tail biting outbreaks (TBOs). However, as TBOs are inevitable, even in well managed farms, it is crucial to know how to manage TBOs when they occur. We evaluated the effectiveness of multi-step intervention protocols to control TBOs. Across 96 pens (1248 undocked pigs) managed on fully-slatted floors, 40 TBOs were recorded (≥3 out of 12-14 pigs with fresh tail wounds). When an outbreak was identified, either the biters or the victims were removed, or enrichment (three ropes) was added. If the intervention failed, another intervention was randomly used until all three interventions had been deployed once. Fifty percent of TBOs were controlled after one intervention, 30% after 2-3 interventions, and 20% remained uncontrolled. A high proportion of biters/victims per pen reduced intervention success more so than the type of intervention. When only one intervention was used, adding ropes was the fastest method to overcome TBOs. Removed biters and victims were successfully reintroduced within 14 days back to their home pens. In conclusion, 80% of TBOs were successfully controlled within 18.4 ± 1.7 days on average using one or multiple cost-effective intervention strategies.

Rearing Undocked Pigs on Fully Slatted Floors Using Multiple Types and Variations of Enrichment.

In fully slatted systems, tail biting is difficult to manage when pigs' tails are not docked because loose enrichment material can obstruct slurry systems. This pilot study sought to determine: a) whether intact-tailed pigs can be reared with a manageable level of tail biting by using multiple slat-compatible enrichment; b) whether a variation of enrichment has an effect; and c) whether pigs show a preference in enrichment use. Ninety-six undocked pigs were given the same enrichment items from one week after birth until weaning. At weaning, four different combinations of 8 enrichment items were utilized based on predefined characteristics. These were randomly assigned to 8 pens (n = 12 pigs/pen). Four pens had the same combination (SAME) from assignment and four pens switched combinations every two weeks (SWITCH). Individual lesion scores, interactions with the enrichment, and harmful behaviours were recorded. The average tail score during the experiment was low (0.93 ± 0.02). Only one pig in a SAME pen had a severely bitten tail (partly amputated). The overall level of interaction with enrichment did not decline over time. Pigs interacted with a rack of loose material most frequently (p < 0.001). The study showed promising results for rearing undocked pigs on fully slatted floors using slat-compatible enrichment.

Erratum: Martin, J.E., et al. Welfare Risks of Repeated Application of On-Farm Killing Methods for Poultry. Animals 2018, 8, 39.

The authors wish to make the following correction to their paper[...].

Welfare Risks of Repeated Application of On-Farm Killing Methods for Poultry.

Council Regulation (EC) no. 1099/2009 on the protection of animals at the time of killing restricts the use of manual cervical dislocation in poultry on farms in the European Union (EU) to birds weighing up to 3 kg and 70 birds per person per day. However, few studies have examined whether repeated application of manual cervical dislocation has welfare implications and whether these are dependent on individual operator skill or susceptibility to fatigue. We investigated the effects of repeated application (100 birds at a fixed killing rate of 1 bird per 2 min) and multiple operators on two methods of killing of broilers, laying hens, and turkeys in commercial settings. We compared the efficacy and welfare impact of repeated application of cervical dislocation and a percussive killer (Cash Poultry Killer, CPK), using 12 male stockworkers on three farms (one farm per bird type). Both methods achieved over 96% kill success at the first attempt. The killing methods were equally effective for each bird type and there was no evidence of reduced performance with time and/or bird number. Both methods of killing caused a rapid loss of reflexes, indicating loss of brain function. There was more variation in reflex durations and post-mortem damage in birds killed by cervical dislocation than that found using CPK. High neck dislocation was associated with improved kill success and more rapid loss of reflexes. The CPK caused damage to multiple brain areas with little variation. Overall, the CPK was associated with faster abolition of reflexes, with fewer birds exhibiting them at all, suggestive of better welfare outcomes. However, technical difficulties with the CPK highlighted the advantages of cervical dislocation, which can be performed immediately with no equipment. At the killing rates tested, we did not find evidence to justify the current EU limit on the number of birds that one operator can kill on-farm by manual cervical dislocation.

Determination of stable reference genes for RT-qPCR expression data in mechanistic pain studies on pig dorsal root ganglia and spinal cord.

RNA expression levels for genes of interest must be normalised with appropriate reference or "housekeeping" genes that are stably expressed across samples and treatments. This study determined the most stable reference genes from a panel of 6 porcine candidate genes: beta actin (ACTB), beta-2-microglobulin (B2M), eukaryotic elongation factor 1 gamma-like protein (eEF-1), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), succinate dehydrogenase complex subunit A (SDHA), Ubiquitin C (UBC) in sacral dorsal root ganglia and spinal cord samples collected from 16 tail docked pigs (2/3rds of tail amputated) 1, 4, 8 and 16weeks after tail injury (4 pigs/time point). Total RNA from pooled samples was measured by SYBRgreen real-time quantitative PCR. Cycle threshold values were analysed using geNorm, BestKeeper and NormFinder PCR analysis software. Average expression stability and pairwise variation values were calculated for each candidate reference gene. GeNorm analysis identified the most stable genes for normalisation of gene expression data to be GAPDH>eEF-1>UBC>B2M>ACTB>SDHA for dorsal root ganglia and ACTB>SDHA>UBC>B2M>GAPDH>eEF-1 for spinal cord samples. Expression stability estimates were verified by BestKeeper and NormFinder analysis. Expression stability varied between genes within and between tissues. Validation of most stably expressed reference genes was performed by normalisation of calcitonin gene related polypeptide beta (CALCB). The results show similar patterns of CALCB expression when the best reference genes selected by all three programs were used. GAPDH, eEF-1 and UBC are suitable reference genes for porcine dorsal root ganglia samples, whereas ACTB, SDHA and UBC are more appropriate for spinal cord samples.

Characterization of short- and long-term mechanical sensitisation following surgical tail amputation in pigs.

Commercial pigs are frequently exposed to tail mutilations in the form of preventive husbandry procedures (tail docking) or as a result of abnormal behaviour (tail biting). Although tissue and nerve injuries are well-described causes of pain hypersensitivity in humans and in rodent animal models, there is no information on the changes in local pain sensitivity induced by tail injuries in pigs. To determine the temporal profile of sensitisation, pigs were exposed to surgical tail resections and mechanical nociceptive thresholds (MNT) were measured in the acute (one week post-operatively) and in the long-term (either eight or sixteen weeks post-surgery) phase of recovery. The influence of the degree of amputation on MNTs was also evaluated by comparing three different tail-resection treatments (intact, 'short tail', 'long tail'). A significant reduction in MNTs one week following surgery suggests the occurrence of acute sensitisation. Long-term hypersensitivity was also observed in tail-resected pigs at either two or four months following surgery. Tail amputation in pigs appears to evoke acute and sustained changes in peripheral mechanical sensitivity, which resemble features of neuropathic pain reported in humans and other species and provides new information on implications for the welfare of animals subjected to this type of injury.

Application of a handheld Pressure Application Measurement device for the characterisation of mechanical nociceptive thresholds in intact pig tails.

The assessment of nociceptive thresholds is employed in animals and humans to evaluate changes in sensitivity potentially arising from tissue damage. Its application on the intact pig tail might represent a suitable method to assess changes in nociceptive thresholds arising from tail injury, such as tail docking or tail biting. The Pressure Application Measurement (PAM) device is used here for the first time on the tail of pigs to determine the reliability of the methods and to provide novel data on mechanical nociceptive thresholds (MNT) associated with four different age groups (9, 17, 24 and 32weeks) and with proximity of the target region to the body of the animal. We recorded an overall acceptable level of intra-individual reliability, with mean values of CV ranging between 30.1 and 32.6%. Across all age groups, the first single measurement of MNT recorded at region 1 (proximal) was significantly higher (P<0.05) than the following two. This was not observed at tail regions 2 and 3 (more distal). Age had a significant effect (P<0.05) on the mean thresholds of nociception with increasing age corresponding to higher thresholds. Furthermore, a significant effect of proximity of tail region to the body was observed (P<0.05), with MNT being higher in the proximal tail region in pigs of 9, 17 and 24weeks of age. There was also a significant positive correlation (P<0.05) between mechanical nociceptive thresholds and age/body size of the animals. To the best of our knowledge, no other investigation of tail nociceptive thresholds has been performed with the PAM device or alternative methods to obtain mechanical nociceptive thresholds in intact tails of pigs of different age/body size. The reliability of the data obtained with the PAM device support its use in the measurement of mechanical nociceptive threshold in pig tails. This methodological approach is possibly suitable for assessing changes in tail stump MNTs after tail injury caused by tail docking and biting.

Avian reflex and electroencephalogram responses in different states of consciousness.

Defining states of clinical consciousness in animals is important in veterinary anaesthesia and in studies of euthanasia and welfare assessment at slaughter. The aim of this study was to validate readily observable reflex responses in relation to different conscious states, as confirmed by EEG analysis, in two species of birds under laboratory conditions (35-week-old layer hens (n=12) and 11-week-old turkeys (n=10)). We evaluated clinical reflexes and characterised electroencephalograph (EEG) activity (as a measure of brain function) using spectral analyses in four different clinical states of consciousness: conscious (fully awake), semi-conscious (sedated), unconscious-optimal (general anaesthesia), unconscious-sub optimal (deep hypnotic state), as well as assessment immediately following euthanasia. Jaw or neck muscle tone was the most reliable reflex measure distinguishing between conscious and unconscious states. Pupillary reflex was consistently observed until respiratory arrest. Nictitating membrane reflex persisted for a short time (<1 min) after respiratory arrest and brain death (isoelectric EEG). The results confirm that the nictitating membrane reflex is a conservative measure of death in poultry. Using spectral analyses of the EEG waveforms it was possible to readily distinguish between the different states of clinical consciousness. In all cases, when birds progressed from a conscious to unconscious state; total spectral power (PTOT) significantly increased, whereas median (F50) and spectral edge (F95) frequencies significantly decreased. This study demonstrates that EEG analysis can differentiate between clinical states (and loss of brain function at death) in birds and provides a unique integration of reflex responses and EEG activity.

The impact of prenatal stress on basal nociception and evoked responses to tail-docking and inflammatory challenge in juvenile pigs.

The consequences of tail-docking (at 2-4 days) and prenatal stress (maternal social stress during the 2nd third of pregnancy) on baseline nociceptive thresholds and responses to acute inflammatory challenge were investigated in juvenile pigs in two studies. Nociceptive thresholds were assessed on the tail root and on the hind foot using noxious mechanical and cold stimulation before and after acute inflammatory challenge by intradermal injection of 30 µg capsaicin (study 1) or 3% carrageenan (study 2) into the tail root. Four groups of 8 (study 1, n=14-16 pigs/treatment) or 5 (study 2, n=6 pigs/treatment/sex) week-old pigs were exposed to the main factors: maternal stress and treatment (docked vs. intact tails). In study 1, tail docking did not significantly alter thresholds to noxious mechanical stimulation, whilst prenatally stressed pigs had significantly higher baseline thresholds to noxious mechanical stimulation on the tail root and on the hind foot than unstressed pigs, whether tail-docked or intact. Capsaicin injection induced localised mechanical allodynia around the tail root in all treatment groups, but had no effect on noxious plantar mechanical responses; however prenatally stressed offspring exhibited significantly attenuated response thresholds to capsaicin compared to controls. In study 2 tail docking did not alter thresholds to either mechanical or noxious cold stimulation. Baseline response durations to noxious cold stimulation of the tail root were significantly shorter in both sexes of prenatally stressed pigs, whilst male but not female prenatally stressed pigs exhibited significantly higher baseline thresholds to mechanical stimulation than controls, although results in female pigs tended towards significance. Carrageenan injection into the tail root induced localised mechanical and cold allodynia in all treatment groups, effects that were attenuated in prenatally stressed pigs. Collectively, these findings indicate that prenatal stress can induce long-term alterations in nociceptive responses, manifest as a reduced sensitivity to noxious mechanical and cold stimulation and evoked inflammatory allodynia. Neonatal tail-docking does not lead to long-term alterations in nociception in pigs.

Development of a mechanical stimulator and force measurement system for the assessment of nociceptive thresholds in pigs.

A mechanical stimulator and force measurement system was developed to quantify withdrawal thresholds to noxious mechanical stimulation of the foot in young pigs. The device and associated PC software have design and control features not previously used in other mechanical stimulators. The device, capable of delivering stimulus rates between 2 and 17 mm/s, maximum force 27 N, was validated in a cross-over study on 8 juvenile pigs (6-8 weeks of age) to check the repeatability and reliability of force threshold measurement and assess its ability to measure changes in force threshold following an inflammatory challenge. Threshold force measurements were obtained over several time periods before and after the pigs received a 0.25 ml subcutaneous injection of 3% carrageenan in 0.01 M phosphate buffered saline (PBS) or PBS in the hind foot. Consistent withdrawal thresholds were measured in injected (ipsilateral) and contralateral feet, 24 h and 30 min prior to injection (mean 8.4; 95% CI 7.1-9.7 N). Carrageenan injection, but not PBS injection, induced a significant decrease in withdrawal thresholds 90 min after injection (4.6+/-0.9 N) which remained reduced for 6h after injection. The testing system provided reliable and reproducible measurements of foot withdrawal thresholds to noxious mechanical force in young pigs (weight range 32-39 kg), and was capable of detecting and monitoring changes in threshold sensitivity following the induction of acute local inflammation in the foot. The system is suitable for studying nociceptive mechanisms in pigs.

Pre-natal stress amplifies the immediate behavioural responses to acute pain in piglets.

Pre-natal stress (PNS) or undernutrition can have numerous effects on an individual's biology throughout their lifetime. Some of these effects may be adaptive by allowing individuals to tailor their phenotype to environmental conditions. Here we investigated, in the domestic pig Sus scrofa, whether one possible consequence of a predicted adverse environment could be altered pain perception. The behavioural response of piglets to the surgical amputation ('docking') of their tail or a sham procedure was measured for 1 min in piglets born to mothers who either experienced mid-gestation social stress or were left undisturbed throughout pregnancy. A behavioural pain score was found to predict the docked status of piglets with high discriminant accuracy. Piglets exposed to PNS had a significantly higher pain score than controls, and for each litter of tail-docked piglets, the average pain score was correlated with mid-gestation maternal cortisol levels. The data presented here provide evidence that the experience of stress in utero can result in a heightened acute response to injury in early life. Speculatively, this may represent an adaptive alteration occurring as a consequence of a pre-natal 'early warning' of environmental adversity.

Changes in muscle cell cation regulation and meat quality traits are associated with genetic selection for high body weight and meat yield in broiler chickens.

Between-breed genetic variation for muscle and meat quality traits was determined at eight weeks of age in 34 lines of purebred commercial broiler and layer lines and traditional breeds (categories) of chickens. Between-breed genetic variation for plasma ion concentrations and element concentration in muscle dry matter and ash were determined. Plasma from broilers had higher concentrations of Na+, K+, Mg++, total and free Ca++ and lower free:total Ca++ than plasma from layer and traditional lines. Muscle from broilers contained more Na and higher concentrations of K, Mg and Ca per mg of ash but not of dry matter compared with layer and traditional lines. In comparison with layer and traditional lines, broiler genotypes were over three times heavier, their plasma creatine kinase activity (CK), a marker of muscle tissue damage, was higher, their breast muscle colour was lighter (L*) and less red (a*) and yellow (b*) in appearance, the initial and final pH of their muscles were lower, the pH change was higher and their breast muscle was more tender. Thus, genetic selection for broiler traits has markedly altered cation regulation in muscle cells and may be associated with changes in muscle cell function and the development of pathology and meat quality problems.

Putative nociceptor responses to mechanical and chemical stimulation in skeletal muscles of the chicken leg.

Electrophysiological responses of nociceptive sensory afferent fibres in the skeletal muscle of the chicken (Gallus domesticus) were examined using mechanical and chemical stimulation. The activity of single nociceptive afferent fibres was recorded from micro-dissected filaments of the fibular and lateral tibial nerves, which innervate the fibularis longus and lateral gastrocnemius muscles. Seventeen putative nociceptive fibres were identified by mechanical stimulation (muscle compression). Conduction velocities (CVs) ranged from 2.8 to 11.3 m/s (mean 5.8; S.E.M.+/-0.9 m/s). Response thresholds to tissue compression ranged from 38 to 126 kPa (mean 81; S.E.M.+/-4 kPa). Increases in pressure intensity, above individual fibre thresholds (x2 moderate; x3 noxious), produced intensity dependent increases in discharge rates. Fibres exhibited slowly adapting, irregular discharges lasting the duration of the stimulus and showed no spontaneous activity in the absence of mechanical stimulation. Intramuscular injection of acetic acid (1% v/v in isotonic saline; pH 2.8) in to the receptive field area stimulated discharge activity in 13 of the 17 (76%) pressure sensitive fibres. Acid injection resulted in prolonged irregular single or intermittent clustered discharges, which continued beyond the 15-min recording period. This study demonstrates the existence of nociceptive sensory fibres in chicken skeletal muscle that are able to respond to and encode acute tissue threatening and subjectively painful stimuli. The physiological characteristics of these nociceptive afferents are consistent with mammalian group III skeletal muscle nociceptors. These findings support the suggestion of a common, acute nociceptive response function in skeletal muscle in avians and other vertebrate classes.