Does phenotypic selection for fleece weight reduce lamb survival?

A two year field experiment studied the impact of phenotypic selection for clean fleece weight (CFW) on 'whole ewe' performance using highly fecund medium wool Merinos stocked at either 10 or 15dse/ha. Post-mortem autopsy was undertaken on all lambs found dead (25%) during lambing in each year. Of those lambs with stomachs present for post-mortem, 92% had not fed. Birthweight and birth type significantly affected post-natal mortality and dystocia was responsible for 61% of all deaths. Fat score at mid-pregnancy was significantly and positively associated with post-natal mortality. Fat score in late pregnancy had a significant negative relationship with birthweight. CFW phenotype did not affect fat score at mid-pregnancy or post-natal mortality (P = 0.059)