This experiment was designed to investigate how feed restriction during rearing and genetic strain affect the aggressiveness of male domestic fowl at sexual maturity. We
used commercial laying strain males to examine the effects of feed restriction during rearing and thus avoided the confounding effects of obesity in full-fed broiler breeder
males. Behaviour of laying strain males fed ad libitum during rearing was compared with that of males feed-restricted to the same degree as in broiler breeder production.
Behaviour of broiler breeder males was compared with that of Old English Game males, a strain traditionally bred for its fighting behaviour. Since commercial laying strain
males had shown low levels of aggression to females in our previous research they were used as controls. Our hypothesis was that feed-restricted laying strain males would show
higher levels of aggression than males fed ad libitum during rearing. We also expected that broiler breeder males would show levels of aggression similar to that of Old English
Game strain males and much higher than that of commercial laying strain males. Aggressiveness was determined using a standardised test in which we recorded re-
sponses to a model of a cockerel in a standing, non-threatening posture.
2. Animals, materials and methods
Sexually mature males were observed in each of four treatments. Treatments con- sisted of broiler breeder males which had been reared and maintained with feed
Ž .
restricted according to the management guidelines BR , commercial laying strain males Ž
. which had been reared and maintained with feed provided ad libitum LA , commercial
Ž .
laying strain males which had been reared and maintained with feed restricted LR and Ž
. Old English Game males reared and maintained with feed provided ad libitum GA .
Twenty-four Ross broiler breeder males and 48 ISA Brown commercial laying strain males were purchased from local hatcheries as day-old chicks and were housed at the
OMAFRA Arkell Poultry Research Station. All chicks were vaccinated for the standard local diseases and were neither dubbed nor toe trimmed. Commercial laying strain males
were randomly assigned to either full-fed or restricted treatments. Males were reared in 3.35 m = 3.65 m pens, with pine shavings as litter. At 1 week of age chicks were
wing-banded for identification and beak-trimmed to prevent feather pecking. Lighting
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regime followed recommendations for broiler breeder stock Ross Breeders, 1997 with 8 h of light until 21 weeks of age and gradually increased thereafter to 16 h of light
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05:00–21:00 at 25 weeks of age. The BR males were feed-restricted according to the Ž
. management guideline for that strain Ross Breeders, 1997 . The LA males were fed ad
libitum throughout the experiment. Feed restriction of LR males was such that their body weight was maintained at the same percentage of full-fed body weight as with
Ž .
broiler breeders of equivalent age North and Bell, 1990 . All males were weighed weekly during rearing and were fed a standard mash grower diet daily.
At sexual maturity, nine males were selected from each group and placed in individual pens. Selection was made from males that were in the middle range of body
weight for that group and was based on good conformation of feet and legs and red comb colour. Pens for LR and LA males were 1.83 m = 1.22 m. Due to space
limitations broiler breeder males were housed in 1.52 m = 1.52 m pens in a separate
room of the same building. All pens had wire mesh walls and pine shavings on the floor. All males had visual access to neighbouring males.
Ž .
Nine Old English Game males Pine Albany strain were obtained on loan from a local breeder. While cock-fighting is illegal in Canada, it is still legal in some states in
the USA. The parental stock of these birds were imported for show purposes from New York State and the breeder confirmed that the males loaned for use in these experiments
were one generation removed from fighting or ‘‘pit’’ stock. All birds were hatched and brooded by an Old English Game female and reared out of doors in a group of mixed
age and sex. Prior to sexual maturity males were individually penned with visual access, but no physical access to other males. All Game fowl were obtained at approximately 28
weeks of age. Birds were neither beak-trimmed, toe-trimmed nor dubbed. Since GA males had been individually housed prior to sexual maturity, they were sexually
inexperienced, but had received social experience when immature with mature and immature females.
Due to concern for disease transmission GA males were housed at the OMAFRA Isolation Unit of the University of Guelph. Males were individually housed in 1.22
m = 1.22 m pens with pine shavings on the floor and a perch located 0.61 m above the floor. Because these males were extremely aggressive, pens were solid sided to prevent
fighting and threatening between neighbouring males. Males could see other males through the barred pen door, but could not reach them to fight. At the request of the
breeder, all GA males were fed ad libitum a mixture of standard breeder mash, pigeon seed, scratch grains and fresh fruit. Despite the flighty nature of these birds, they had
been handled frequently and seldom showed aggression to people. However, certain males were extremely aggressive and had to be handled with care.
Males of all strains were approximately 31 weeks of age when testing began. Our aggression test consisted of recording responses of the males to a model of a male
conspecific. Aggression in domestic fowl has been found to be more common between Ž
. individuals which are similar in appearance Lill, 1968 . A Barred Rock male was
chosen for our model as its mottled black and white plumage was markedly different from that of the three male strains tested and hence would affect males equally. The
individual Barred Rock male used as the model weighed approximately 3.5 kg, whereas the average weights of BR, LR LA and GA males were 5.4, 2.3, 2.8 and 2.1 kg,
respectively, when the experiment concluded at 39 weeks of age. A relaxed and non-threatening pose was chosen in the belief that a threatening Barred Rock male may
look more intimidating to the smaller GA, LA or LR strain males than to the large BR males. Also, motivation of males to initiate rather than respond to aggression was of
particular interest, as females rarely initiate aggression with males.
The model was developed by suspending a euthanised Barred Rock male in a sling attached to two dowling rods. He was then essentially made into a marionette or puppet
by arranging his appendages and head using strings. As this was accomplished prior to rigor mortis, the posture of the bird was easily manipulated such that his head was
elevated, beak held level and wings lay close to his body. His eyes were left closed for fear that freezing might affect the structure of the eyeball, making the model less
convincing. In addition, one would expect a bird with its eyes closed to be perceived as
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being non-threatening, although perhaps a bit unusual Fig. 1 . After being placed in a
Fig. 1. Frontal view of frozen Barred Rock male model in the Plexiglas box.
freezer for 24 h, the sling and strings were removed and the model was stored in a large plastic bag in the freezer.
When the model was removed from the freezer for approximately 1.5–2.0 h during testing, minimal damage was observed as a result of thawing, likely due to the insulating
value of feathers. When first removed from the freezer some frosting up of the comb and wattles was observed. Testing was not initiated until 5–10 min after the model was
removed from the freezer, by which time these appendages thawed enough to appear reddish-pink and life-like. The model was placed in a 0.6 m = 0.6 m Plexiglas box as
protection from physical contact with the males during the test.
Testing was performed in a separate room in the same building in which the birds Ž
. were housed. The test pen measured 1.2 m = 2.4 m with solid sides Fig. 2 . Bird mesh
was attached to the top of the pen to avoid escapes and also along the front of the pen, acting as a door. Pine shavings were placed 3 cm thick on the floor. A video camera was
placed on a tripod approximately 1 m from the front of the pen, allowing a panoramic view through the bird netting. At the back of the pen was a 0.6 = 0.6 m open front wire
cage covered with a cotton sheet. This cage served as a starting box for the test male. The cotton sheet was attached to rope, allowing the experimenter to pull the sheet away,
exposing the open cage front, while remaining out of sight of the bird. The Plexiglas box was situated at the front of the pen and within the box the model stood facing the wire
cage and test male. The distance from the open front of the cage to the Plexiglas box containing the model was 1.0 m.
Fig. 2. The arrangement of the test pen. The cotton sheet has been raised, allowing the test male to see and approach the model.
Testing procedure involved carrying a male in an upright position from his home pen to the wire cage. As males were accustomed to being handled, they appeared relaxed
and displayed little fear as a result of being carried. In fact, some individuals crowed or gave food calls while being carried to the test room during the second round of testing.
Visual access to the model was obstructed while the male was placed in the wire cage and the cotton sheet placed across the open cage front. After allowing the male to
acclimatise to the cage for 1 min, the cotton sheet was removed. The male was then able to interact with the model through the Plexiglas. Behaviour was video-recorded for 15
min, after which the male was caught and returned to his home pen.
Males were tested individually. No other birds were in the test room, however some auditory contact with other birds in the building existed. Three birds were tested every
second evening between 17:00 and 18:00, with males from the same treatment tested during the same week. This time was chosen because it is known that sexual behaviour
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in domestic fowl increases later in the day Lake and Wood-Gush, 1956 . Each male was tested once and then tested again 4 weeks later. Since the first test was followed
immediately by another experiment in which males were placed with three females for Ž
. 26 h Millman and Duncan, unpublished data , males were sexually inexperienced
during the first aggression test, but had received limited sexual experience 4 weeks prior to the second aggression test.
Ž Videotapes were analysed using the Observer software program Noldus Information
. Technology, 1993 . Frequencies of behavioural elements were recorded over 15 min.
Durations of time spent ground pecking and in an alert posture were also recorded.
Ž .
Descriptions of behavioural elements were in accordance with Wood-Gush 1956 . Frequencies of the following behavioural elements were recorded over 15 min —
threats, waltzes, crows, wing flaps and ground pecks. Durations of time spent ground pecking and in an alert posture were also recorded.
Since some males did not perform some behavioural elements, the data set contained a large number of zero values, skewing the distribution from normality. Logarithmic
transformation improved the normality of the data; however as zero values tended to be concentrated in certain treatments, variance was not homogeneous. For this reason,
non-parametric statistical analysis was felt to be more appropriate and was performed using SAS NPAR1WAY procedure on mean frequencies and differences in frequencies
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between the first and second aggression test SAS Institute, 1985 . The Kruskal–Wallis test on Wilcoxon scores of ranked sums was used to determine if there was a significant
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difference between treatments. A Tukey-like test for multiple comparisons Zar, 1984 was used to determine which of these treatments differed.
During the rearing phase males were housed together, with one pen per treatment. One could argue this resulted in one replication of each treatment. However, housing
males individually at such an early stage of development would have radically affected their social behaviour at maturity and would have masked any differences resulting from
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Fig. 3. Frequencies of waltzing displayed during tests 1 and 2. Mean frequencies of waltzing S.E. and difference in frequencies of waltzing between the two tests were statistically significant where letters differ.
feed restriction during rearing. Also, we wished our research to have relevance to commercial conditions where birds are reared in very large group sizes and further
reducing group size in our experiment would have reduced the application of our results. Feed-restricted birds display extreme aggression and mobbing at the feeder during
feeding, which could affect social behaviour at maturity. We reared twice the number of birds required for behavioural observation, in an attempt to maximise group size during
rearing. Ideally, we would have reared nine pens of males per treatment from which one male would be tested, but this was not possible due to space limitations at the research
facility and concerns of the number of animals used for this research. As males were individually housed at sexual maturity and observations did not commence for another
10 weeks we felt justified in treating the nine males within each treatment as replications and not an experimental unit.
3. Results
