Previous findings have shown a difference in attack latencies, i.e., aggression, between reciprocal F1's of a line selected for short attack latency (SAL) and a line selected for long attack latency (LAL). In the present study, we investigated the influence of postnatal maternal environment on attack latency scores (ALSs). The results show that only the evolution of the ALSs over 3 consecutive days is influenced by crossfostering. Accordingly, we conclude that the postnatal maternal environment affects ALSs only to a small extent.