It’s also worked with Dunedin-based dairy research provider, Abacus Bio, to develop new economic models.
Although the emphasis placed on residual survival and fertility is now much greater no new traits have been added to the BW calculation. There had been talk of late lactation body condition score (BCS) becoming a trait with an economic value in its own right but it has remained in the background as part of calculations for several of the seven existing traits:
- Fat
- Protein
- Milk volume
- Liveweight (LWT)
- Residual survival
- Fertility
- Somatic cell count (SCC).
NZAEL manager Jeremy Bryant said BCS hadn’t been added because NZAEL wanted to ensure the assumptions behind the calculation of BCS economic value were technically and practically sound and that its direct inclusion would accelerate genetic gain in BW.
“We weren’t yet comfortable so we decided to delay its potential inclusion for another year to allow us to explore it further,” he said.
Profit impact
Fertility and survival were consistently mentioned in submissions as having an increasing impact on overall farm profitability.
“It costs more than $1300 to rear a heifer to her first calving, and once she calves you want her to calve year after year so you have a high proportion of the herd at the peak productive age of four to eight years old.”
“These concepts are built into the newly developed economic model for residual survival and fertility that along with models for all traits have been developed by Dr Peter Amer and his Abacus Bio team in conjunction with high calibre scientists that form the Standing Advisory Committee of NZAEL.”
Amer is recognised as a world-leading authority on this work and the estimation of residual survival economic value by NZAEL has also been through a rigorous national and international review process.
The need to breed a robust cow for NZ conditions came through strongly in the national breeding objective review and has been reflected in the new economic values. Traits other than production (TOP) such as owner opinion, milking speed and udder overall are included in the estimation of the residual survival trait breeding value. The lift in the economic value of residual survival has lifted the TOP traits effective emphasis in BW.
Bryant said the use of the new seasonal drymatter (DM) economic values from the DairyNZ and NZ Plant Breeders and Research Association (NZPBRA) forage value index (FVI) initiative will allow more detailed and accurate exploration of traits that impact on how much feed a cow needs at specific times of the year (Dairy Exporter, December, page 25).
For instance it will be used within the fertility economic value calculation to consider the opportunity cost to supply feed in early lactation to early-calving cows or the costs of feeding later-calving cows which need extra feed in summer as they peak later and produce more in late lactation.
Previously the opportunity cost of feed was fixed throughout the year.
Fertility status
Bryant said breeding companies themselves have been putting more emphasis on fertility over the last few years and once the new BW calculation is applied some bulls may have a higher BW thanks to their better fertility status now being given greater recognition.
The main changes to the model calculations for BW overall has been the adoption of the latest energy requirement equations from DairyNZ and a move to a four-year historical, plus one-year forecast for milk prices and farm costs as opposed to 10-year historical averages.
Bryant said milk processors had been reluctant to provide longer forecast prices for the calculations but NZAEL would be looking for further milk processor engagement in the future.
Although weightings in BW for production traits such as protein have dropped that’s been a factor of accommodating the increased weightings given to residual survival and fertility.
Bryant said the economic values for production traits have only altered minimally and overall fat and protein still make up more than 40% of the weightings with milk volume taking that to over 52%.
LWT has a slightly more negative economic value than it did previously going from -$1.48/kg to -$1.52.
