Opportunities and challenges for improving OAD response
The response of cows to once-a-day (OAD) milking varies between breeds and at the individual animal level.
A 4-year DairyNZ trial comparing cows that are milked OAD and twice-a-day (TAD) showed that Jerseys are more tolerant towards the effects of OAD milking compared with Holstein-Friesians. However, there is greater phenotypic variation in milksolids production within the Holstein-Friesian breed - suggesting an opportunity to breed cows suited for OAD milking.
DairyNZ contracted AbacusBio to conduct industry-good research on the genetic improvement of OAD milking. For milk traits, while there are minimal differences between OAD and TAD systems in the economic value per kilogram of milk fat or protein or per litre of milk, 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.
A key challenge for developing genetic improvement schemes, NZAEL (New Zealand Animal Evaluation Limited) manager Dr Jeremy Bryant says, is the relatively small number of cows on whole-season OAD milking.
"50, 000 cows would need to be genotyped in order to achieve sufficient power in genomic selection, which was discouraging, 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," Jeremy says.
"The low numbers involved meant a OAD sire-proving scheme is unlikely given the level of investment that would be required by a breeding company to pursue it."
"A key opportunity, however, for improving OAD herd genetics is through culling on the cow side of the equation due to better herd reproductive performance relative to TAD systems."
DairyNZ and NZAEL are currently considering options for the genetic improvement of sires for whole-season OAD milking systems.
Photo credits to NZX Agri