Multiple Trait Selection for Maternal Productivity

1. Multiple Trait Selection for Maternal Productivity D. H. Crews, Jr., P. B. Mwansa and R. A. Kemp Agriculture and Agri-Food Canada Research Centre, Lethbridge, AB

2. What is maternal productivity? • Reproductive rate • Age at puberty • Heifer pregnancy rate, calving ease and 3 yr old rebreed rate • Persistence into profitable parities • Calf growth • Direct genetics for growth • Maternal genetics  milk production • Cow maintenance requirements • Weight • Intake Low heritability, Difficult evaluation Everyone already does this Can’t measure this

3. Data and Information • One obstacle to new index development is capturing information on “new” traits • We are often limited by what data is routinely and comfortably recorded in national databases You want to measure what?!?

4. Measure This Growth Cow weight Calves ÷ Reproductive years Evaluate This Maternal Productivity Moo. What is your MPI? Multiple Trait Selection

5. Trait Definitions • Direct weaning weight • Maternal weaning weight • Cow weight at calf weaning • Indicator for maintenance costs • Stayability • Pr(3 | 1) = probability that a female will have at least three calves given she became a dam

6. Multiple Trait Selection Index: Objective • The selection objective was to increase genetic potential to consistently wean heavy calves while maintaining input costs which yielded an aggregate genetic value function: MPI = v1 WWT + v2 MLK + v3 CWT + v4 STY with resulting economic weights: v1 = 1.17 v2 = 0.98 v3 = -0.14 v4 = 2.39

7. CWTd STYd WWTpe WWTm WWTd BWTm BWTd BWTd 0.48 BWTm 0.11 WWTd 0.74 0.19 -0.34 0.18 WWTm -0.24 0.24 WWTpe CWTd 0.67 0.85 -0.17 0.50 0.07 STYd -0.45 -0.44 0.01 MPI NCE Genetic Parameters -0.48

8. Relative Emphasis • The relative contribution of component traits to variation in the index • Weaning weight = 30% • Milk = 25% • Cow weight = 13% • Stayability = 27%

9. Making the MPI User Friendly • The MPI can be interpreted as any other EPD • It is a combination of EPD with relative economic values • The units are $ differences • Information packaging is an important part of making indexes useful selection tools rather than only marketing tools • The MPI can be expressed with any mean and variance • e.g. mean = 100, SD = 25

10. MPI Validation • What differences in animals are we evaluating? • Is the MPI the same as selection for component traits? • Separation of MPI evaluation into high and low groups • High = > 2 SD greater than the mean MPI (n = 17,328) • Low = > 2 SD less than the mean MPI (n = 11,496) • Comparison of standardized component EPD between groups • What component traits are most related to the MPI?

11. STY CWT MLK WWT -10 0 5 10 -5 Component Traits in High and Low MPI Groups

12. To Summarize… • The MPI was developed with the breeding objective to increase genetic potential to consistently wean heavier calves over a sustained productive life while maintaining input costs • Annual or generational genetic trend is expected to be positive for all component traits, however, cow weight increases would be minimal • As a multiple trait index, component trait values vary: • Animals with different component EPD have similar MPI

13. … Summary • The MPI places more relative emphasis on maternal characteristics and stayability than on growth • Accuracy and intensity are greatly reduced when data (information) is lacking on grandprogeny • MPI selection is not equivalent to selection for any of the component traits alone • Validation with maternal indexes is a challenge • MPI validation is still largely to be conducted • The MPI needs to be expanded to include more components, which will come with data

14. Thank you dcrews@agr.gc.ca 403-317-2288