The most interesting differences that are found in 18 week broiler breeders are those of the TI test. A shorter TI-duration in ED small birds compared to Skip small birds may indicate increased stress in Skip birds. As the birds are now much larger, however, the argument of variation in agility as an effect of body size has to be taken into consideration. Skip small birds were significantly larger than were ED small birds and since no difference were found in latency to first headmovement, which would be less affected by body size, this could be interpreded as an artefact of size differnences. However between the ED small and ED large birds there was both a tendency towards ED small birds displaying shorter TI duration as well as a tendency towards displaying shorter latency to first head movement compared to ED large birds. This indicate that small birds may be less fearful, and potentially less stressed, compared to large birds also at 18 weeks of age.

Most of the differences found in 4 week old broiler breeders did not persist to 18 weeks of age. There is little surprise in that no differences are found regarding vocalizations (during the TI test no vocalizations were at all performed) as the motivation for social contact decrease with age, especially in a potentially threatening situation. However, this may not necessarily mean that social tolerance and social support is not an important factor also at this age regarding their actual home environment.