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Results – minimal individual EBV change

For the purposes of this fact sheet, only the change in 200 Day Growth EBVs of sires in Cohort 3 are presented, however similar findings were observed across other traits and cohorts analysed in this project.

How Much Did EBVs Change?

Minimal change was observed, on average, in the EBVs of sires in cohort 3 of the ASBP for 200 Day Growth.

The average EBV of all cohort 3 sires when initially entered in the ASBP was +45 kg, whereas their average EBV of the sires once their progeny had been performance recorded was +46 kg, representing a change in average EBV of only 1 kg.

Similarly, the average EBV of the 10 sires with the lowest and highest initial 200 Day Growth EBVs was +34 kg and +53 kg respectively, versus an average 200 Day Growth EBV once their progeny had been performance recorded of +35 kg and +56 kg (Table 1).

How Much Did EBVs Change for each Individual Sire?

While there was minimal change, on average, in the 200 Day Growth EBVs of sires in cohort 3 of the ASBP, the EBVs for some individual sires did change.

A comparison of the initial and final 200 Day Growth EBVs for each sire is presented in Figure 1. In this graph, the grey bars represent the initial EBVs of each sire when first joined in the ASBP, while the red bars represent the final EBVs of each sire at the end of the project when all progeny performance data had been included in the EBV calculation.

While the EBVs for some sires increased, some decreased and some remained unchanged, there was not a significant amount of re-ranking observed. That is, the EBV of a sire who had a low initial EBV may have increased, but the sire’s EBV would still be relatively low by comparison to other sires. With a small number of exceptions, bulls that started off with high 200 Day Growth EBVs also finished the program with high 200 Day Growth EBVs, while sires that started with lower 200 Day Growth EBVs also finished with lower 200 Day Growth EBVs.

How Accurate Were the Initial EBVs of the Sires?

An accuracy figure is produced alongside each BREEDPLAN EBV, providing an indication of the amount of information used in the calculation of that EBV. The higher the accuracy, the more likely the EBV is to predict that animals true breeding value and the less likely that EBV is to change.

The average accuracy for the 200 Day Growth EBVs of sires entered in cohort 3 of the ASBP was relatively low at 71% (Table 2), indicating that some change in the EBVs of individual sires was expected when the sires’ progeny were performance recorded.

Were the Changes in the EBVs of Individual Sires Within Expected Ranges?

The possible change in the initial EBV for each sire can be quantified by assessing the standard error of the EBV, with the standard error differing based on the accuracy of the sire’s initial EBV.

The initial EBV for each sire is not expected to change more than one standard error for 7 out of every 10 sires. For the statistics enthusiasts, this is based on the distribution of expected change following a normal bell curve (Figure 2).

Upon analysis of the change in 200 Day Growth EBVs for each initial sire in cohort 3 of the ASBP, it was observed that the EBVs for 75% of sires (30 out of 40) did not change more than one standard error. The changes observed in sire EBVs (in standard errors) is displayed in Figure 3.

This bar graph demonstrates that there was slightly less change in the EBVs of individual sires than was expected (i.e. 75% v 68.2%), indicating that the changes in sire EBVs, were within expected ranges.

Further details regarding the change in EBV for each individual sire, relative to the change that was expected (1 standard error) is shown in Figure 4.  In this graph, the orange dots represent the final EBV, whereas the blue bars represent a range of 1 standard error outside the initial EBV for each sire. Sires with a smaller standard error are indicative of a higher initial EBV accuracy.

As described above, the EBVs were expected to remain within one standard error (blue bar) for 7 of out every 10 sires.