There has been a change to how calving difficulty data is displayed as part of ICBF's January 2020 genetic evaluations.
Earlier this month, its board approved the implementation of these changes, in this proof run, which went live on Monday, January 27th.
With the new update, the ICBF explained, the calving difficulty PTA % will be split into two: dairy heifer calving difficulty PTA % and dairy cow calving difficulty PTA %. "These will reflect the truer incidence of on-farm calving difficulty."
"This is a considerable change to how we as an industry have understood the calving difficulty figures."
Until now, each bull had a single calving difficulty PTA (and reliability), which provided an indication of the expected incidence of calving difficulty, irrespective of the type of female that bull was mated with.
"Until now, farmers considered bulls with a calving difficulty PTA of less than around 2.4% and a high reliability as ‘safe’ on heifers; this will no longer be considered best practice." the ICBF explained.
From herein, the advice from ICBF is to use the calving difficulty figures relevant to the type of female to be bred, such as a heifer or cow.
The ICBF explained that when selecting bulls for use on cows, use the dairy cow calving difficulty PTA (and associated reliability).
When selecting bulls for use on heifers, use the dairy heifer calving difficulty PTA (and associated reliability).
To help with the change-over to this new method of displaying calving difficulty, the ICBF developed a ready reckoner.
This said this will aid farmers in the transition from the single calving difficulty PTA to the two new traits: dairy heifer calving difficulty PTA % and dairy cow calving difficulty PTA %.
The purpose of the ready reckoner is to help farmers to visualise the change from one single calving difficulty PTA to two and how this varies between heifers and cows.
ICBF said it will be posting a ready reckoner and further information to all HerdPlus farmers over the coming weeks.