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
Feed restriction of laying strain males during the rearing phase was successfully accomplished without causing undue hardship. Feed restriction as practised in the broiler
Ž .
Fig. 4. Frequencies of crowing displayed during tests 1 and 2. Mean frequencies of crowing S.E. and difference in frequencies of crowing between the two tests were statistically significant where letters differ.
breeder industry is severe and results in stereotypic pecking, increased drinking and Ž
. increased activity suggestive of frustration and suffering
see Section 1 . Casual observation during the rearing phase indicated such behaviour was performed by both
broiler breeder and by feed-restricted laying strain males. Broiler breeder males also behaved aggressively during the rearing phase, often chasing and pecking each other.
Aggression was not as pronounced in feed-restricted laying strain males, which may indicate differences in severity of feed restriction or strain differences in responses to
feed restriction. However, only casual observations were taken at this time. Feed restriction delays maturity and laying strain males developed secondary sexual character-
istics and crowed at a later age than males fed ad libitum. Body weight continues to
Ž increase during the breeding phase in feed-restricted broiler breeder males
Ross .
Breeders, 1997 , but body weight of ad libitum fed males reaches a maximum and levels off at an earlier age. Hence, the percentage of ad libitum body weight attained by
Ž feed-restricted males increases as the birds age. In our previous research Millman et al.,
. 1996, 1997 , we found feed-restricted broiler breeder males were 80 of the body
weight of ad libitum fed males at 37 weeks of age. Similarly, in the current experiment feed-restricted laying strain males were 82 of the body weight of males fed ad libitum.
Fig. 5. Frequencies of wing flapping displayed during tests 1 and 2. Mean frequencies of wing flapping Ž
. S.E. and difference in frequencies of wing flapping between the two tests were statistically significant
where letters differ.
As expected, Game males were the most aggressive. Whereas threats occurred at very low frequencies and were not found to differ significantly between treatments, Game
Ž males waltzed more than 10 times as frequently as did males of other strains Fig. 3,
. Ž
P - 0.001 . Crowing also was performed significantly more by Game males Fig. 4, .
P - 0.05 . Both crowing and waltzing were found to increase significantly in Game Ž
. males during the second test P - 0.005 and P - 0.05, respectively . One Game male
attempted a flying attack on the model through the Plexiglas and casual observation of Game males indicated they were also considerably more aggressive in their home pens.
Males attempted to fight with each other through the solid walls of their pens despite visual restriction and some males behaved aggressively to human handlers, which was
never observed in males of the other treatments.
Wing flapping occurred at much lower frequencies than did crowing or waltzing and Ž
. was rarely observed in full-fed males Fig. 5 . Wing flapping was highly variable among
individuals. Feed-restricted laying strain males showed significantly more wing flapping Ž
. than did full-fed laying strain and Game males P - 0.005 and wing flapping by broiler
breeder males approached being significantly greater than that shown by full-fed laying strain and Game males. Frequency of wing flapping did not change significantly over
the two tests for any of the treatments.
Fig. 6. Frequencies of ground pecking displayed during tests 1 and 2. Mean frequencies of ground pecking Ž
. S.E. and difference in frequencies of ground pecking between the two tests were statistically significant
where letters differ.
Ž Feed-restricted laying strain males performed the most ground pecking Fig. 6,
. P - 0.05 suggesting that they too were affected by conflicting motivations. Since
broiler breeder males showed the lowest levels of ground pecking in both frequency and duration, this display cannot be accounted for simply as foraging due to feed restriction.
Game and full-fed laying strain males were intermediate in frequency and duration of ground pecking and for both of these treatments, ground pecking significantly increased
Ž .
during the second test P - 0.01 . Although auditory signals were not recorded, casual observation indicated that feed-restricted laying strain, full-fed laying strain and Game
males tended to give food calls when they were being carried to the pen in the second test. It is possible that males, due to their prior experience with females in the test pens 4
weeks earlier, were anticipating contact with females. However, this does not explain why feed-restricted laying strain males ground pecked at high levels during the first test.
Alert behaviour was highly variable among individuals and was not found to differ significantly between treatments. Broiler breeder males did not show high levels of alert
behaviour. Clearly, the low level of aggressive behaviour by broiler breeder males was not a result of overriding fearfulness in males of this strain. Game males showed a
significant increase in alert behaviour during the second test when compared with
Ž .
full-fed laying strain males P - 0.001 . Interestingly, although Game males appeared to be more alert in the second test, they also displayed more waltzing and crowing. This
suggests that either aggressive motivation in Game males was high enough to override their fearfulness or that the alert response may have been more indicative of arousal than
fearfulness.
4. Discussion
