Poor lamb survival in the Australian Merino has been recognised as a problem since the late 1950's. From the numerous studies cited in the literature, starvation is ultimately the cause of most lamb deaths but there may also be many intermediate effects involved. These may include dystocia, ewe/lamb interactions, climate and nutrition. While dystocia and starvation appear to be distinct causes of lamb deaths, sub-lethal birth trauma may result in the animal dying of starvation through low vigour or simply an incapacity to follow its mother. Two methods of overcoming the problem of lamb mortality are management and genetic selection. Management has met with limited success and incurs an annual cost. Improvements obtained through breeding however are permanent. The major thrust of the study reported here deals with identifying behavioural and physiological indicators of maternal ability using two flocks that have been shown to differ genetically in their capacity to rear lambs. The first of these flocks was the Trangie Fertility Flock, the ewes of which have a superior capacity to rear their lambs than those of the second flock, the Trangie Random Flock. The differences between these two flocks were arrived at by genetic selection
