“Rob of cause you are right, but not everyone agrees that GMI is the major cause AND sights individual bulls that have let us down. They forget all the ones that they are thriving on.
Now must be the time to add a fertility element to the index, or if not that take serious considerstion of the trait when bull selecting. We are only second worse to the Holsteins in calving interval by 4 days the next worse is 8 days better than us.
With new GMI about 135 points lower that before the base change we can still find enough sires of sires who can score 200+ even when we have used the fertility PTA X 40. This is the amount needed to holt the increase in calving interval let alone strongly reduce it.
A report done by the SAC on fertility in Guernseys by Eileen Wall concluded that there had been no significant deteroriation in the Guernsey figures as based on her research of NMR calving data. This report was available on the WGCF site until the recent update of that site and presumably can still be obtained from the WGCF secretary Bill Luff.
The fertility Indexes published by Dairy Co have a range of -14 to +14 and each point represents half a day, so a daughter of a bull that is -14 will be expected to take 7 days longer to settle back in calf. These daughters are also generally higher yeilding.