Effect of Time of Joining on Reproductive Wastage in Merino Sheep

An experiment of factorial design was conducted to quantify variation in the components of reproductive wastage in Merino ewes following artificial insemination (AI) in either January, March or May. Semen from 6 individual rams was used in either fresh or deep frozen form, the latter providing a ram "control" to identify variation in wastage as of either paternal or maternal origin. Results showed comparatively little difference in either ovulation or fertilisation rates between the 3 times of AI. There was, however, highly significant variation in lambing rate with best results following AI in March and poorest results in January. Depressed fertility in January was associated with a much higher incidence of embryo wastage. Despite generally reduced fertility, AI with frozen semen produced an identical pattern of lambing between January, March and May to that achieved with fresh semen. The results indicate that most variation in reproductive wastage was due to changes in the level of embryo mortality associated with failure of maternal, rather than paternal mechanisms. (