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Dutch Pigeon Transporter Study 1995 Study which informed design of modern transporters Rate Topic: -----

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Posted 2 July 2010 - 11:56 AM

WAU dissertation no. 2003.


J Gorssen

Department of Animal Husbandry, Wageningen Institute of Animal Science, PO Box 338, 6700 AH Wageningen, The Netherlands

Date: 1 November 1995

Transport is an essential component of racing pigeon contests. Preliminary studies showed that adverse conditions on the transporter may contribute to pigeon losses. In these experiments, the physical and social aspects of the transport environment were studied in relation to the racing pigeons’ behaviour and how they control their body heat (thermoregulation). In all experiments, the pigeons were confined in a transport crate for at least 23 hours. A combination of continuous heat exposure and water deprivation resulted in the pigeons losing body weight. The birds’ body temperatures also increased leading to an increase in overall heat production. The effect of ambient temperature on overall heat production varies both between, and within the day and night periods. Water deprivation also affects this day/night variation. Fluctuating temperatures increased activity amongst the birds and led to further loss of body weight. The space allowance levels during transport (then) used, led to predominantly aggressive behaviours within the pigeons, and the levels of aggression didn’t decrease over time. Aggressive behaviours caused further heat production, as well as head injuries, although less severe in hen than cock crates. When more space was allowed, the levels of major head injuries and aggression-related behaviour decreased.

General Introduction pp3-5

Transport of pigeons: An outline

Dynamic cycle in racing pigeon contests




The internal physical environment of the Transporter is made up of:

a) Climate - temperature, air humidity, air velocity
B) Air composition
c) Light duration & intensity
d) Husbandry – water and feed availability

1990 Dutch transporter conditions:

e) 200 crates, 30 pigeons per crate.
f) No additional cooling facilities.
g) Forced ventilation fans of insufficient capacity for a fully loaded truck.
h) Heat transfer to outside dependant upon air cooling through natural ventilation while vehicle was in motion.
(i) Internal temperature depends on outside temperature and the temperature control methods the driver takes during stops.
(j) Missing a temperature control stop increases internal temperatures by around 12C within 30 minutes. The difference between internal and outside temperatures increases from 6C to 18C, accompanied by an increase in air humidity.

The racing season covers late spring and summer, the warmest parts of the year. Combination of warm outside conditions and inadequate internal climate control supports driver and convoyer perceptions that ‘heat exposure’ was the biggest factor on board the transporter. The main way a pigeon keeps its body cool is heat loss through water evaporation from the lungs. The study showed pigeons lost on average 9% of their body weight, while the maximum loss was 14% body weight… and this is before the race even begins.

Transporter: The internal social environment. The main feature was the high numbers in the crate. 1990 guidelines prescribed 225cm2 per pigeon for 24/48hours journey; 250cm2 for 48/72hours; and 300cm2 for over 72 hours.
(These guidelines were being followed at the time with 40 birds in a 9000 cm2 crate).

Sexes, young and old are segregated into separate crates, although some young pigeons may be mixed together because the sex is not known, or the belief some hold that young cocks are not so aggressive as old cocks. Each crate holds several owners’ birds.

Study focus: At the start, the main focus was on the birds’ ability to regulate their body temperatures at varied temperatures within the transporter, with or without water being available. Experiments took place based on different ages and sexes, which measured the birds heat production, body weight loss and body composition when confined for different periods (up to 23 hours) during both day (hot) and night (cold) conditions. Towards the end, attention was given to the behavioural effect heat and crowded conditions had on the birds. Thermoregulation (the bird’s ability to control its body heat) and behaviour were found to be very important factors in pigeon transportation.


There was growing concern about pigeon losses amongst pigeon fanciers and Dutch society. Problems with orientation and navigation combined with adverse weather conditions after release were the usual reasons given for these losses. However, pigeon fanciers became aware that transport conditions were a possible explanation for sudden peaks in losses. Poultry transport research supported this view. Instances of dead on arrival are higher during summer, and increase the longer the journey. Heat exposure on newly hatched chicks not only killed birds at the time, but over the 2 week period following exposure the number of deaths increased, even under normal housing conditions. Racehorse transport research also showed their performances decreased too following dehydration.

A second reason for the research was a growing awareness of possible animal welfare problems during transport. There were few facts and figures on pigeons in transport. The research ran from 1990-95, funded by the Dutch Homing Union (NPO) and financially supported by the Dutch veterinary service, Ministry of Agriculture, Nature Conservation and Fisheries, the equivalent of DEFRA in the UK.

Study Outline p7

In the beginning temperature and water availability were the main factors of interest. Insight into their effects on pigeons was needed as the then literature on these subjects was poor, with nothing on groups of pigeons in transit, or their social behaviour and activity patterns within the crate.

Chapter 1 pp13/23

Optimal Temperature Levels for Racing Pigeons Housed under Transport Conditions: The Role of Water Availability and Age.


The effect of water availability and age on the optimal temperature zone for pigeons aboard the transporter was studied. The upper critical temperature (UCT) was estimated based on body heat production, body weight & composition losses. 40 groups x 15 young birds, and 40 groups x 15/18 old birds were studied over 23 hours, exposed to ambient temps between 15C and 39C, with or without access to water. On the optimal temperature zone, age had no effect while water availability had strong impact. Birds with access to water had no UCT. Variation in weight loss occurred above 32.1C; Water deprivation caused dehydration, and deaths occurred at 39C. Body heat production increased by 0.16% per degree C above 32.1C (UCT). Above 32.1C body weight loss increased by 1.3% per degree C. The resultant dehydrated state from water deprivation and heat exposure may increase bird losses.

Results pp16-

Heat production significantly affected by ambient temperature and bird’s age. YBs 0.36% higher than OBs. Water availability had no effect.

Body Weight loss significantly affected by ambient temperature and water availability. No upper critical temperature was found with birds having water availability, while 32.1C estimated for birds without water. Variation higher in young birds 23.8% than old birds 21.2%.

Mean Body Weight (dry matter, breast muscle) significantly affected by interaction between ambient temperature and water treatment. Upper critical temperature 32.1C for water-deprived birds, higher temperatures, dry matter increased by 0.83% per degree C. i.e. most of the water lost came from the bird’s breast muscles.

Humidity: 70% up to 35C; 64% @ 37C; 56% @ 39C.

Respiration quotient 0.74, unaffected by exposures.

Hematocrit (Hct) values (Dehydration causes higher values) significantly affected by bird’s age: YBs 55.7%, OBs 53.6%. Water deprivation tended to increase Hct by 1.2%.

Hematocrit explanation
Hematocrit values decrease when the size or number of red cells decrease, and if red cells increase Hematocrit increase values. Fluid volume in the blood affects the hematocrit. Pregnant women have extra fluid, which dilutes the blood, decreasing the hematocrit. Dehydration concentrates the blood, increasing the hematocrit.

Chapter 1 Discussion pp20-22

Water availability and the ‘thermoneutral’ zone – (optimal temperature zone)
Water deprivation lowers the upper critical temperature to 32.7C. (YBs died at 39C)

With water availability, no increase in these values was seen below the upper limit at 37C. With water availability and increasing ambient temperatures a decrease in heat production values was seen until 20C was reached, and remained constant at higher levels. 20C can be regarded as the lower critical temperature. (LCT)

At high ambient temperature levels birds resort to mainly water evaporation for heat loss to maintain normal body temperature. Water deprivation prevents repletion of body water reserves. This results in an increase of 1.3 % body weight loss per degree C above 32.1C and reaches 16.2% body weight loss at 39C, over a 23 hour period. The physiological consequences of this weight loss (dehydration) are: a rise in body temperature; blood high viscosity (‘thickening’); ‘drying out’ of the breast muscles through water extraction; and death when the body weight loss threshold reaches 18%. The combined effects of the temperature level and the time birds are exposed to it determines the mortality rate. Heavier birds are affected more. Smaller birds appear better able to cope with hot environments where water is scarce.

During flight, decreased blood viscosity promotes blood flow thus reducing the load on the heart. Therefore dehydration will adversely affect flight performance, and the bird’s capacity to get home.

Also during flight, body temperature increases by between 1.5C and 3C, and water loss exceeds water production. Starting the flight with depleted water reserves will cause the pigeon’s body to overheat (hyperthermia). In horses, hyperthermia decreases the time to muscle fatigue.

Group behaviour: One parameter increased above 32.1C, regardless of age or water availability – variation of body weight loss. Social interactions within group of confined pigeons increased body heat production, and consecutively, the need for individuals to lose that heat. Water availability doesn’t equate to individual intake either due to social inhibitions and drinking thresholds. Climate control during transport is useful when water is available, keeping the temperature below 32C reduces the variation of body weight loss within a group and thus the variation in individual hydration status of the birds at the time of release.

Age and optimal temperature zone p23

Optimal temperature zone for transporter: 20C to 32C for all ages. Some parameters were different for different age groups.

Body heat production was 5% higher in young birds than old. Young birds have higher energy requirements for growth processes.

Young birds also had a higher variation in mean body weight losses, may be down to lack of experience. Old birds easily adapt to an already familiar environment. Hct values significantly higher in young birds 2.1%, possibly linked to the higher body heat production, requiring a higher oxygen supply.

UCT is 32C. Variation in body weight loss increases above this. Water deprivation increases heat production, body weight loss, dry matter content of the breast muscles and mortality at temperatures above UCT. The resultant dehydrated state probably reduces the flying capacity of the pigeon and increase bird losses.

Chapter 2 pp28-38

Duirnal Variation in the Thermogenic Effect of Ambient Temperature on Pigeons as Affected by Water Deprivation.

Introduction p28

If climate control is inadequate, pigeons are at risk to periodic or chronic exposure to high ambient temperature. The thermoneutral zone - a temperature range that doesn’t cause the bird any problems - is bordered by an upper critical limit (UCT) above which the bird suffers heat strain. At temperatures below the lower critical limit (LCT) the bird suffers cold strain. The birds’ metabolic response to fluctuating temperatures differs between light and dark periods, the birds are less able to respond when temperatures fall below the LCT during rest periods (darkness) compared to active periods (light). Body heat production differs within and between these day/night periods, and loco-motor activity also affects this variation as activity increases body heat production and may influence body heat loss too.

80 birds (4 groups of 15/18 birds) were exposed to 10 constant ambient temperatures between 15C and 39C. The impact of water deprivation on and between different day/night periods (15 hours Light / 9 hours Darkness in August, to 10 hours Light /14 hours Darkness in October) and the effects of ambient temperature, UCL, heat strain and cold strain were studied. Birds had access to, or no access to water. Exposure period 1000 to 0945 next day with lights out 2030-0730. Some birds couldn’t cope at 39C without water.

Results pp31-35.

Total heat production and activity-free heat production decreased during the first hours of exposure. Towards lights off, total heat production increased, activity free heat production didn’t. In the 18 hour period from 1030 to 0230 next day Activity-related heat production almost doubled from 10.6% to 19.5% and respiratory quotient decreased from 0.8% to 0.7% (fasting level). Activity periods during the dark were low and increased immediately following lights on resulting in total heat production 7.3% between 0730 and 0930.

Discussion p36

Water deprivation and diurnal variation in upper critical temperature

Upper critical temperature found for water deprived birds (32C) [No thermoneutral zone, LCT=UCT, no diurnal variation] but not for those having access to water, which had a thermoneutral zone.

Water deprivation and diurnal variation in cold strain p37

Cold strain was twice the value during daylight than darkness. This is because of a food-deprivation / sleep effect at onset of darkness and present only during darkness.

Spinal thermosensitivity to heat increases during darkness (Graf, 1980). This results in panting at a spinal temperature that is more than 1C lower compared with light. The spinal cord threshold temperature for inducing an increase in heat production decreased with the number of days’ duration of food deprivation. This fasting effect was found during the night only. Differences in thermoregulatory behaviour between wakefulness and sleep may partially account for the lower cold sensitivity of heat production during darkness. Two daylight maxima present for cold strain – one shortly before onset of darkness, the other shortly after lights on; Variation during darkness too, cold strain increases from 0230 onwards.

Cold strain differences between light and darkness periods are caused by circulating melatonin which controls the bird’s circadian rhythms and thermoregulatory mechanisms.

Water deprivation and diurnal variation in heat strain p38

The combination of high ambient temperatures and water deprivation only resulted in significant increase in heat production after 10 hours…occurring at onset of darkness consistent with the lowered temperature thresholds during darkness. Respiratory rates increase after darkness, with a resulting increase in body heat and rise in heat strain. The overall increase in heat strain might be a result of dehydration with its increased circulatory energy requirements brought about by increasing blood viscosity and increased heat production due to a higher body temperature (van Hoff effect). For transport, this implies that it is not just the level of heat, but combination of water deprivation, temperature level and duration of exposure that determines the intensity of thermoregulatory stress the pigeon experiences.

Chapter 3 pp43-57

Duirnal Variation in the Thermoregulation of Group Confined Pigeons in Relation to Ambient Temperature and Water Deprivation.
Abstract p43

The thermoregulatory response of a group of pigeons to water deprivation and their ability to recover from the resultant dehydration was examined. Groups were deprived of food, and exposed to constant temperatures of 23, 31 or 37C over 48 hours. A 24-hour dehydration period was followed by a 24-hour recovery period during which heat production and body temperature (Exp1) and evaporated water loss (EWL) (Exp2) were measured. Combined results gave an estimated dry thermal conductance during lights on and lights off periods. EWL indicated UCT between 31C and 37C. At 23C and 31C, water deprivation did not affect body temperature, EWL or heat production. At 37C water deprivation increased body temperature and reduced EWL from 8 hours after exposure began, onwards, whereas heat production was not affected. Within 30 minutes of re-hydration the effects of previous dehydration disappeared. Dry thermal conductance increased with ambient temperature. At 37C conductance of dehydrated birds was lowered.

Introduction p43

From a welfare viewpoint, not only the momentary effect of adverse conditions on the pigeon’s thermoregulation is of interest, but also its ability to recover. Dehydrated pigeons almost fully replenish body water reserves within 30 minutes when given access to water.

Discussion p54

Effects of water deprivation

During dehydration period, the effects of water deprivation on body temperature and EWL depended on ambient temperature and exposure time. Total heat production depended only on ambient temperature. At 23C and 31C, water deprivation did not affect thermoregulatory parameters. At 37C, body temperature increased, and EWL decreased, possibly due to osmotic trigger to save body water levels. Dehydration results in increased serum electrolyte and protein concentrations, and osmotic stress reduces respiration frequencies which causes a skip to behavioural thermoregulation to maintain normal body temperature.

Increase in Body heat and decrease in EWL developed from 6/8 hours after start of water deprivation, at 37C, birds had evaporated 3.9% of their body weight as water, total body water content assumed @ 65%. Heat exposed pigeons become dehydrated during lights off even when water is available.

Chapter 3 – contd

Recovery from dehydration p55

Within 30 minutes of taking water ( drank 7% of body weight = mean weight loss ) body temperature and body weight returned to normal. EWL recovery was slower.

Diurnal variation in dry thermal conductance : the role of ambient temperature and dehydration pp56-57

Activity of group confined pigeons consists mainly of aggressive social interactions: pecking, threatening and running away causes Total heat production, EHL and body temperature to increase, resulting in heat storage in the body. Heat stress reduces capillary blood flow to the inner organs allowing maximum heat loss at the body surface, but loco-motor activity causes a shift in this blood flow to the muscle tissues reducing this surface heat loss, and reducing dry thermal conductance.

Chapter 4 pp61-74

Activity and Thermogenesis in pigeons exposed to temperature fluctuations


Data on heat production and body weight loss showed that when temperatures fluctuated 15/22C the pigeon can cope; but at 35/42C, the pigeon was put at risk, and birds died in the experiments. The temperatures chosen simulated colder April races and warmer July races. Activity levels (aggression) maxima occurred after 5 hours and 3 hours after confinement. Bodyweight loss for the higher temps were 11.8% to 15%, and 17.1% for the dead bird. 280cm2 per bird equivalent to overcrowding.

Chapter 5 pp79-93

Behaviour and Thermogenesis of Group Confined pigeons under crowded conditions

Abstract p79

Racing pigeons are transported to the race points under crowded conditions. In a first experiment, Old cocks were exposed to 26C or 36C, access to water or deprived, for one day. No significant effects on behaviour or heat production. However, the frequency of threatening behaviour and the proportion of activity related heat production within total heat production increased during the experimental period. Behaviour patterns differed between pecked and non-pecked birds but remained constant. Pecked birds showed more cyclic transitions between immobility and retreat, and there was no extinction in pecking behaviour. In the second experiment, birds segregated by age and sex with access to water were exposed to 36C. Young birds were more immobile yet heat production was higher. Cocks had higher activity-related heat production, pecked more and had more head injuries than hens, and behaviours didn’t diminish with time…there was no adaptation. Birds must be transported in less crowded conditions.

Introduction pp79-80

Dutch transport guidelines range from 225 to 300cm2 space allowance per bird. Conditions may compare to overcrowded roosts where serious fighting may take place. Racing season extends from April to September, inadequate climate control may expose the pigeons to risks of heat exposure during summer, leading to increased aggression. Combination of heat exposure and water deprivation results in dehydration with unclear affects on bird’s behaviour in crowded crates. When pigeons reach 6 months old, little difference in aggressive behaviour between ‘old’ birds and ‘young’ birds.

Behavioural elements videotaped: Mobile - drinking, preening, stretching, shaking, roosting (lying with feathers fluffed and rump patch visible), pecking (with or without contact), wing beating, wing twitching, bowing display (fixed or rotating). Additionally - immobility (standing still, feathers tight, rump patch covered) retreat (as a result of aggressive behaviour) hiding (lowering the head and hiding it under the tail or breast of another pigeon) looking around (horizontal or vertical) and walking (not due to aggression) were included.

Behavioural elements were grouped into categories: Avoidance included retreating and hiding, Threatening consisted of wing twitching & bowing; Autonomous covered roosting, looking around and walking; Grooming covered preening, shaking and stretching.

Areas of damage around the eyes and beak were scored from 0 to 8 (severe).

Results p83

Experiment 1 involved 80 pigeons, housed at Uni for one year, 8 groups of 10; old cocks only, water / no water 26C and 36C. September.

EXP1 26C 36C
Category DW AW DW AW S/error Unit
Immobile 72% 66% 63% 74% 4%
Threaten 17% 18% 20% 14% 4%
Autonomous 9% 13% 11% 9% 3%
Avoidance 0.7% 1.4% 3% 1% 1%
Grooming 0.6% 0.9% 0.3% 0% 0.4%
Peck-no/c 4 7 14 7 5% Times/bird
Peck-cont 2 4 9 4 3% Times/bird
B/W loss 8% 8% 12% 8% 2%

Experiment 2 involved 80 pigeons, had been racing and housed at Uni for 3 weeks, 8 groups of 10; sex and age segregated; water available, 36C to mimic high summer temperatures. October.

EXP2 26C 36C
Category DW AW DW AW S/error Unit
Immobile 69% 71% 57% 57% 4%
Threaten 14% 13% 21% 16% 3%
Autonomous 12% 10% 8% 13% 3%
Avoidance 2% 2% 11% 9% 5%
Grooming 1% 2% 0.4% 2% 1%
Peck-no/c 7 8 9 11 2% Times/bird
Peck-cont 4 3 5 4 1% Times/bird
B/W loss 9% 8% 6% 6% 1%

Time effects p85

In groups of 10, the occurrence of aggressive behaviour did not diminish over time, and the proportion of activity-related heat production and threatening behaviour increased with time. OBs more than YBs.

The relative body weight loss of young birds was 8.5% compared with 6% for old birds.

EXP2 26C 36C
DW AW DW AW S/error Unit
Young cocks Young hens Old cocks Old hens
Tot HP 8 7 7 7 0.1% W-kg
ActfreeHP 6 6 5 5 0.1% W-kg
Ac/totHP 0.2% 0.2% 0.3% 0.2% 0%
Wounds 2% 1% 2% 1% 0.3%

Discussion pp91-93

Behaviour patterns: persistence of aggressive behaviour with time. P91

Group size is an important determinant for developing fixed hierarchy within group. Lower ranked pigeons are more mobile (avoidance) more at risk of injury. Immobility is the best defence against aggressive attack.

Relative body weight determines rank – heavier birds, more aggressive, more immobile.

Relation between behaviour patterns, heat production and body weight loss pp92-93

EXP1 : Pigeons housed in crowded conditions are not able to decrease activity levels during heat exposure. Immobility / reduction in activity would have been expected to conserve body water – opposite was seen - 36C beyond UCT?

EXP2: Young pigeons had higher activity-free heat production than Old birds, yet a lower body weight (not fully grown). Higher metabolism due to growth may explain higher heat production (Blaxter 1989) and may also explain 2.5% higher body weight loss through increased EWL at higher temperatures. If this water loss is not compensated by a higher water intake, more body weight is lost. Water intake was rarely observed due to experiment design. Time spent immobile was 13% higher in young birds, which may show general ‘inactive’ tendency, including going to the drinker.

Chapter 6 pp97-109

Effect of Crate Space Allowance and Sex on Behaviour and Thermogenesis of Racing Pigeons

Abstract p97

Racing Pigeons Behaviour and Thermogenesis were studied in relation to Sex and Space Allowances. Over 23 hours, 20 groups of cocks or hens were confined in crates at one of 5 space allowance levels. At 210 cm2 the birds were immobile for 85% of the time. At 630 cm2 that reduced to 37%, autonomous and grooming behaviour increased while activity-related heat production decreased. Reference space per bird is 350 cm2 . At 630 cm2 no injuries occurred. Injuries increased 5-fold at 280 cm2 and 9-fold at 210 cm2, with 0-risk at 420 cm2 . Cocks were 3-times more at risk of injury than hens.

Introduction pp97-99

Birds are confined in crates from periods ranging between 12 and 72 hours, during which they are exposed to high ambient temperatures. Group confinement is comparable to an overcrowded roosting site and gives rise to aggressive behaviours in which pigeons defend a space around themselves. This leads to injuries and extra activity that produces additional heat.

Dutch Homing Union transport guidelines range from 225 (below 24 hours) to 300 cm2 (24 - 72 hours) per bird…without evidence of effect or requirements. The study set out to establish the effect space allowance has on behaviour, heat production and injuries.

100 old cocks and 100 old hens were assigned to 20 same sex groups of 10 birds. 5 different space allowances were tested: 210, 280, 350, 420 and 630 cm2 per bird. Water was available, but no food. Temp 36C, Humidity 66%. Experiment duration 1030 to 0945 next day, with lights off between 2030 and 0730. Behaviours were videotaped during 4 x 30-minute periods beginning 1200, 1600, 2000 and 0800 next day, and grouped into the same categories as the previous experiments in Chapter 5.

Results p103

Space cm2 210 280 350 420 630
Sex C H C H C H C H C H
Immobile 85% 80% 70% 70% 65% 70% 50% 55% 45% 40%
Autonomous 1% 5% 18% 20% 25% 20% 20% 30% 40% 45%
Groom 0% 0% 1% 2% 2% 3% 2% 2% 10% 15%
Threaten 8% 8% 11% 8% 5% 5% 20% 9% 12% 9%
(%total heat production) 20% 18% 16% 15% 15% 12% 28% 12% 15% 11%

Other than activity (heat production) the table shows the % of time taken up by the observed behaviour.

As in the previous experiments in Chapter 5, injuries around the eyes and beak were scored from 0 to 8 (severe). Table shows frequency distribution for overall injury scores per experiment – number of birds out of 20.

Space cm2 210 280 350 420 630
Sex C H C H C H C H C H
Score 0- 1 2 4 3 6 9 14 9 14 13 19
Score 2- 3 10 11 13 12 9 4 9 6 6 1
Score 4-6 8 5 4 2 2 2 2 0 1 0
Minor injuries total Cocks 36 Hens 57
Major injuries total Cocks..36 Hens..43

Discussion p106

Space allowance per pigeon

Time spent immobile is an indicator of neighbour-dependant behaviour, probably to avoid aggression. Silent, immobile birds evoked the least number of attacks. At low space allowance levels, aggression towards one bird has impact on total heat production for all birds in the same crate. Attacks are also more likely to cause serious injury. An increase in space allowance significantly reduces the risk of eye injuries. Injury not only causes the bird discomfort, it increases the risk of eye infection.

The birds ability to regulate its body heat was less affected by space levels than water availability. At 36C, body weight loss was low, showing continuous water availability is an effective measure for preventing dehydration even at low space levels within the crate. However, the cost of water intake measured in the number of pecks the bird receives is probably higher when space allowance is low, the pigeons’ movements towards the drinker sparking aggression in the nearest birds.

Space allowance effects are different on the sexes p107

Cocks are more aggressive and have higher activity-related heat production and injury scores than hens. Fighting in cocks is different, adapted from fighting on ledges and attempting to hurl an opponent off them, by getting a grip on the skin around the eye and pushing and pulling violently. Cocks are three times more likely to sustain major injuries than hens.

There is of course considerable variation in individual behaviour. Even at the highest space allowance, 7 out of 20 cocks sustained major injuries. Guideline focus was therefore: acceptable average outcome for all the group; or the most vulnerable?

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