At the DairyNZ Great OAD Discussion Group meeting in Masterton in June, DairyNZ scientist Dr Claire Phyn and Dr Jeremy Bryant, manager of New Zealand Animal Evaluation Limited (NZAEL), outlined the current state of play in the OAD genetic improvement environment.
“A common theme that comes through is that Jerseys tend to be more tolerant on average to the effects of OAD milking than Holstein/Friesians. But it is really important to note that within the Holstein/Friesian breed there’s actually a great deal of variation,” Phyn said.
A DairyNZ trial comparing cows milked OAD against cows milked twice a day (TAD), showed that within the Jersey cows used in the trial there was a 41% difference in milksolids production between the top and bottom quartile under TAD milking, and a 48% difference for those milked OAD.
“So there’s a greater variation on OAD between the top performers than on TAD, but it is not a huge difference in the Jersey breed.”
Phyn said it was a different story for Holstein/Friesians in the trial where there was a 34% difference in milksolids production between the top and bottom quartiles under TAD, but a massive 57% difference under OAD.
“What this means is that there is obviously opportunity to breed for OAD milking.”
There is currently no pan-industry genetics initiative focusing on OAD systems. LIC offers a commercial OAD Index that effectively converts TAD breeding values for the milk traits and somatic cell count into OAD breeding values and uses TAD economic values to calculate a OAD index.
DairyNZ contracted Dunedin-based genetics research company AbacusBio to conduct industry-good research into OAD milking genetics improvement.
They modelled economic values for OAD traits. For the milk traits, they found minimal differences between OAD and TAD systems in the economic value per kilogram of milkfat or per litre of milk. Phyn said that was not a surprise as it was in per unit of output.
Somatic cell count was found to be more economically important in OAD herds, and fertility less important, relative to the national breeding worth (BW) index.
“But when you pile it all together it doesn’t actually have a major effect on re-ranking of bulls,” Phyn said.
“However, if you change the breeding values for OAD, the combination of both is important.”
Bryant said the AbacusBio report showed the relatively small number of cows on whole-season OAD milking was a key challenge for developing genetic improvement schemes.
Genomic selection was an option, but to get sufficient power Bryant said about 50,000 cows would need to be genotyped. Given best estimates put the number of whole-season OAD herds in New Zealand at 400-500 or between 2-5% of the national herd, the numbers game was discouraging.
Bryant also said the low numbers involved meant a OAD sire-proving scheme was unlikely given the level of investment that would be required by a breeding company to pursue it.
Bryant said a key opportunity for OAD systems to improve their herd genetics was through culling on the cow side of the equation due to better herd reproductive performance relative to TAD systems.
