CONCEPTION RATES
So far we have dealt with ovarian cycles and the importance of heat detection. Having served our cow, we hope that she will become pregnant. The proportion of cows which hold to service is known as the conception rate.
This may be expressed as the conception rate to first service, the conception rate to all services, or inversely as the number of services per conception. A very good figure would be 65% conception to first service, although 55% is probably average for the national herd and figures of 40% or less are by no means uncommon. The past 10-15 years have seen a fall in conception rates worldwide.| 100 eggs shed | Losses |
| 95 fertilised ova | 5 fertilisation failure |
| 70 survive to 21 days | 25 early embryonic mortality |
| 60 survive to 45 days | 10 implantation failure/ embryonic mortality |
| 55 cows calve | 5 abortions/deaths/culls |
| Total calvings 55 | Total losses 45 |
Table 8.6. The fate of 100 bovine eggs in a herd with good fertility.
These are conception rates, however, and they will be significantly higher than final calving rates. Research has shown that if you take 100 cows a few days after insemination, almost 95% of the eggs shed will have been fertilised and are developing as embryos, but many of these die in the early stages so that by 21 days the number of living embryos has fallen to 70%; that is, 25% have been lost already, and 25% of the cows will return to service. By the stage of manual pregnancy testing at about 45 days, a further 10% of embryos will have been lost partly due to failure of implantation at 30-35 days, and only 60% of the cows are likely to be detectably pregnant to the first service. Allowing a 5% loss from abortion culls and deaths this gives an eventual calving rate of 55%. The stages are shown in Table 8.6. In poor fertility herds losses will be very much higher than this.