LIC | Improving the Improvement Index

Improving the Improvement Index

Rachel BloxhamIn terms of Animal Evaluation (AE) updates, it doesn’t get much bigger than the changes that occurred to the Breeding Worth index during February, says Rachel Bloxham, LIC animal evaluation manager.

Following the February 13 AE run, many farmers will have noticed significant changes in Breeding Worth (BW), Production Worth (PW) and Lactation Worth (LW).

From a cow and herd perspective, the biggest influencing factor was the annual update to the economic values – which, given the fall in dairy returns, took on a good degree of significance this year.

Annual Economic Value (EV) update

The underlying information used in the annual calculation of economic values reflects changes in income and costs for the industry the farmers within it. Annual updates ensures Breeding Worth remains relevant in an ever-changing market environment. New figures are now attributed to economic values (for example, the value of protein has markedly dropped, while the value of fat has slightly increased).

NZAEL enhancements

Aside from the annual economic updates, there were several significant enhancements to the AE system in February.
These included:

  • The addition of the Body Condition Score (BCS) trait to Breeding Worth
  • A change to the model that drives the fertility breeding value
  • The introduction of a 'reproof bias adjustment'
  • Re-estimation of the residual survival breeding value

All changes have most impact on bull evaluations, although there is a less significant impact on the national population. 

“Due to a lower forecast milk price for 2015/16, the main changes this year are an easing in the economic values for milk and protein. Despite the lower milk price, the economic value of fat has remained stable due to an increase in the relative value of fat to protein. The lower five-year rolling average milk price has also caused the (negative) economic value for liveweight to ease slightly, as the opportunity cost of feed to satisfy maintenance requirements has reduced, while cull cow and surplus calf values have remained strong.” - Melissa Stephen, genetic evaluation developer, DairyNZ.

Each of the enhancements are outlined in full on DairyNZ’s website, but a summary is offered below.

1.    Body Condition Score (BCS)

The inclusion of BCS in BW recognises the value of a cow’s ability to hold on to body condition into late-lactation. If a cow is light toward the end of her lactation, the farmer must take action to ensure she regains condition before calving. The farmer can either dry her off early, or feed her more during the autumn and winter (when feed is at a premium). Both options result in lost profit.

The graphic below illustrates the new ‘effective trait weightings’ within BW, following the update to economic values and the inclusion of Body Condition Score (BCS).

BW Traits

2.    Fertility Breeding Value 

Ongoing development work on the transfer of AE operations to NZAEL identified the need to modify the fertility model. The model more efficiently utilises mating records, improving the accuracy of the Fertility BV.

3.    Reproof bias adjustment 

NZAEL research determined that, when a bull is used on a widespread basis, a negative bias is introduced into his BW. It is likely this bias is caused by incorrect recording of parentage.  The scale of this bias has been increasing over time, and, until now, was approaching a level that falls short of international standards.

NZAEL has developed an adjustment method that removes the bias from the Breeding Worth of ‘reproof’ bulls. These reproof bulls are typically (i) born between 2003 and 2006, and; (ii) have gone through a progeny test and now have a second set of reproof daughters from widespread use in the national herd.

The degree of adjustment for each bull is based on his age, breed, and number of widespread reproof daughters. This reproof bias adjustment is a step in the right direction, but it does not entirely address what is recognised as a challenging issue within the industry (and industries worldwide).

DairyNZ says it is committed to ongoing improvement of the genetic evaluation system, and will continue to research alternative correction methods.

4.     Re-estimation of residual survival breeding value

A regression equation is used to estimate ‘Total Longevity’ (not accounted for by the traits making up BW), allowing survival to be included in BW without double-counting.  A refreshed regression equation that relates to the residual survival breeding value has also been introduced to the BW model. The new equation is now more-representative of today’s national population, as well as adjusting for the inclusion of BCS.

Overall Impact on Farmers

Economic Value Update

The impact of the changes discussed above will differ depending on the breeding values and breed make-up of differing herds.

Based on current cow average breeding values, on average the effect is -1 BW, - 13.4 BW, and -9.4 BW for Holstein-Friesian, Jersey and Crossbreds respectively (values are slightly higher for current herd tested cows: -5 BW, - 16 BW and -10 BW respectively.) It is worth noting that just because a herd’s BW may have declined, this doesn’t necessarily correspond to a change in ranking within the national population: Herds of similar breed makeups and breeding values will be affected in a similar manner.  
Farmers are advised to contact their LIC Farm Solutions Manager for their latest cow and herd AE statistics. Overall, February 2016’s changes are designed to enhance utilisation of records and provide more-accurate predictions, better-reflecting the true value of bulls and their daughters.

To read about these changes in more detail, visit DairyNZ website.

This article was published in the Autumn 2016 edition of The Bulletin. To see more, visit The Bulletin page



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