Minimising pregnancy failure and calf loss

Summary

The literature review highlighted that:

- Generally, 90% of cycling females mated to fertile bulls conceive during an oestrus cycle.

- Embryo loss before day 45 of gestation usually accounts for about 75% of total reproductive wastage, with three quarters of this between days 8 and 18 after fertilisation. A benchmark of 50% for established pregnancy rate per cycle was suggested in the literature. Major causes of loss included infectious reproductive diseases, nutritional and environmental factors (that affect folliculogenesis and ova viability), and male factors (sperm attributes; bull behaviour and management), with potential genetic influences insufficiently understood to be quantified.

- Losses between confirmed early pregnancy and weaning in ideal northern Australian situations averages approximately 9%. Losses in the pre-, neo- and post-natal periods can all be high due to a wide range of causes, though infectious diseases and specific nutrient deficiencies appeared most important. Over this period, neo-natal mortalities appeared the highest and most variable, eg, as high as 40%. Key outcomes from the monitor herd studies were:

- Established pregnancy rates per cycle ranged from 40-70% for most groups of cattle, with no primary factors identified as influencing this rate. However, both pestivirus infection and vibriosis were implicated, though not confirmed causes, in some matings with low pregnancy rates per cycle. Neither Neospora spp. nor Leptospira spp. present in all herds could be related to losses.

- A NW Queensland herd experienced losses of over 40% in the neo-natal period due primarily to hypovitaminosis A. Excluding this herd, total loss from confirmed pregnancy to weaning was 11%, with neonatal loss accounting for approximately half of this.