# Presentation: 680870

## Accuracy and stability of national and international somatic cell score evaluations

## Objectives

**Investigate the accuracy and stability of somatic cell score evaluations**
**From US data *****(study one)***** **
**Overall**
**By bull sampling status**
**‘****S’****	****Standard sampling, defined by NAAB**
**‘****O’****	****Other (alternative) sampling**
**From Interbull data *****(study two)***
**For bulls with US evaluations**
**By inclusion of foreign daughters**

## DataStudy One

**20,811**** Holstein bulls born in 1985 or later**
**17,992**** ****	****Sampling status ‘S’**
**	****2819**** ****	****Sampling status ‘O’**
**481,416**** US SCS evaluations from 1995 through February 2004 compared to May 2004 evaluations**
**6,975,946**** pairs of evaluations including all evaluation pairs for each bull**

## MethodsStudy One

**Mean change, absolute change, SD and expected SD of change where:**
**Between each evaluation and the May 2004 evaluation, for all bulls and by sampling status**
**Within all pairs of evaluations, by change in reliability (REL)**

## ResultsStudy One

**Overall, May 2004 PTA SCS were greater than earlier evaluations**
**SD of change in evaluations were larger than E(SD)**
**For evaluations prior to 2000, SD of change averaged ****19%**** larger than E(SD)**
**For later evaluations, SD of change was ****10%**** larger than E(SD)**

## ResultsStudy One

**SD of change exceeded E(SD) more with smaller increases in REL**
**For changes in REL less than .05, SD of change was ****25%**** greater than E(SD)**
**For changes in REL from .10 to .30, SD of change was ****8%**** greater than E(SD)**
**Sampling status can affect accuracy**
**‘****O’**** bull first evaluations changed less but increased less in REL**
**‘****S’**** bull evaluations with an opportunity for 2nd crop daughters more accurate**

## DataStudy Two

**13,624**** Holstein bulls with only US daughters in Interbull evaluations for May 2001**
**1028 ****Holstein bulls with US and additional foreign daughters included in Interbull evaluations**

## MethodsStudy Two

**Correlations of 2001 with 2004 evaluations and regressions of 2004 on 2001 evaluations **
**By increase in US daughters from 2001 to 2004**
**For bulls with Interbull evaluations including:**
**US daughters only (US-only)**
**US and foreign daughters (Multi-country)**

## ResultsStudy Two

|  | Number of bulls |  | Correlation of |  |  |
| --- | --- | --- | --- | --- | --- |
|  |  |  | IB01 with IB04 | US01 with US04 | IB01 with US04 |
| US-only bulls | 13,624 |  | 0.960 | 0.963 | 0.962 |
|  >25% daus1 | 1715 |  | 0.849 | 0.854 | 0.854 |
|  >50% daus1 | 1211 |  | 0.835 | 0.841 | 0.841 |
|  >100% daus1 | 855 |  | 0.829 | 0.835 | 0.836 |
|  >200% daus1 | 569 |  | 0.808 | 0.813 | 0.814 |
| Multi-country bulls |  | 1028 | 0.972 | 0.970 | 0.929 |
|  >25% daus1 | 195 |  | 0.936 | 0.909 | 0.912 |
|  >50% daus1 | 149 |  | 0.926 | 0.889 | 0.905 |
|  >100% daus1 | 102 |  | 0.900 | 0.850 | 0.874 |
| 1Percent increase in US daughters from May 2001 to May 2004. |  |  |  |  |  |

## ResultsStudy Two

|  | Number of bulls |  | Correlation of |  |  |
| --- | --- | --- | --- | --- | --- |
|  |  |  | IB01 with IB04 | US01 with US04 | IB01 with US04 |
| US-only bulls | 13,624 |  | 0.960 | 0.963 | 0.962 |
|  >25% daus1 | 1715 |  | 0.849 | 0.854 | 0.854 |
|  >50% daus1 | 1211 |  | 0.835 | 0.841 | 0.841 |
|  >100% daus1 | 855 |  | 0.829 | 0.835 | 0.836 |
|  >200% daus1 | 569 |  | 0.808 | 0.813 | 0.814 |
| Multi-country bulls |  | 1028 | 0.972 | 0.970 | 0.929 |
|  >25% daus1 | 195 |  | 0.936 | 0.909 | 0.912 |
|  >50% daus1 | 149 |  | 0.926 | 0.889 | 0.905 |
|  >100% daus1 | 102 |  | 0.900 | 0.850 | 0.874 |
| 1Percent increase in US daughters from May 2001 to May 2004. |  |  |  |  |  |

## ResultsStudy Two

|  | Number of bulls |  | Regression of |  |  |  |
| --- | --- | --- | --- | --- | --- | --- |
|  |  |  | IB04   on   IB01 | US04 on US01 | US04   on   IB01 | SE |
| US-only bulls | 13,624 |  | 0.99 | 0.99 | 0.99 | 0.002 |
|  >25% daus1 | 1715 |  | 1.01 | 1.00 | 1.01 | 0.01-0.02 |
|  >50% daus1 | 1211 |  | 1.00 | 1.00 | 1.00 | 0.01 |
|  >100% daus1 | 855 |  | 1.00 | 1.01 | 1.01 | 0.02 |
|  >200% daus1 | 569 |  | 0.99 | 1.00 | 1.00 | 0.03 |
| Multi-country bulls |  | 1028 | 0.98 | 0.98 | 0.89 | 0.01 |
|  >25% daus1 | 195 |  | 0.99 | 0.97 | 0.96 | 0.03 |
|  >50% daus1 | 149 |  | 0.98 | 0.95 | 0.94 | 0.03-0.04 |
|  >100% daus1 | 102 |  | 0.97 | 0.95 | 0.93 | 0.06-0.08 |
| 1Percent increase in US daughters from May 2001 to May 2004. |  |  |  |  |  |  |

## Conclusions

**Mean PTA SCS tended to increase slightly over time and as REL increased**
**Addition of daughters caused greater than expected changes in PTA SCS**
**Correlations and regressions of US and Interbull 2001 and 2004 evaluations were near expectations**
**Foreign data improved prediction of later US PTA**