Ramifications of Selection Decision Support for Cow-Calf Improvement

1. Ramifications of Selection Decision Support for Cow-Calf Improvement Dorian.Garrick@Colostate.edu

2. The Selection Problem • We have some current production environment (cow herd) and corresponding management and economic circumstances • We have many choices as to which bulls we might choose to use to mate to these cows • The decisions will impact the performance of first crop sale offspring, attributes of female replacements and ultimately, many aspects of the whole-ranch system

3. Informed Decisions • The ability to make informed decisions as to alternative sires depends upon quantifying the productivity and economic outcomes from using particular bulls

4. Example Bulls

5. Consider WWD EPDs • The first two bulls (RA4 and RA5) have Weaning Weight Direct EPDs of 56 and 28 respectively • Bull RA4 will wean calves that average 28 lb more than RA5 • We can determine this directly from the EPD without regard for the herd average weaning wt • But how will the daughters of the two bulls perform within a system context

6. Consider WWD & WWM EPDs • RA4 was 56 & 30 where RA5 was 28 & 8 • The daughters differ in WWD EPD by 14 and in WWM EBV by 22 • The daughters calves will differ in weaning weight by 14+22=36 lb

7. Consider HPG EPD • Consider Heifer Pregnancy • RA4 had an EPD of 20 and RA5 was 16 • The difference in their EPDs is 4 • RA5 would produce more non-pregnant yearlings daughters to be disposed of • The effect of this on profit will be influenced by • the marginal value of feed used for the cow herd vs the marginal value of feed used for postweaning • This depends upon the efficiency of gain as well as the relative beef price for weaners vs yearlings

8. Number of daughters • We cannot directly interpret this difference in terms of the number of non-pregnant heifers without recourse to the mean HPG • This is due to the fact that HPG is derived from a threshold model

9. Underlying Scores to Preg Rate Pregnant Heifers Heifers not in calf 20% Truncn pt = 0.84s

10. Underlying Scores to Preg Rate Pregnant Heifers Heifers not in calf 20% Truncn pt = 0.84s 0.38

11. Underlying Scores to Preg Rate Pregnant Heifers Heifers not in calf 20% Truncn pt = 0.84s 12% Truncn pt = 0.84 +0.38/1.17=1.165 Phenotypic s.d. = 1.17 0.38

12. Underlying Scores to Preg Rate 10% Truncn pt = 1.28s 5.5% Truncn pt = 1.28 +0.38/1.17=1.605 Phenotypic s.d. = 1.17 0.38

13. Sensitive to the Average • A shift in the underlying scale of 0.38 for heifer pregnancy would increase pregnancy rate • By 8.0% if average pregnancy rate is 80% • By 4.5% if the average is 90% • Phenotypic “interpretation” of a threshold underlying score depends upon the mean • Published values are at a mean of 50%

14. Consider CED and CETM • The bulls differ a little in direct and maternal calving ease • The impact of these bulls on the number of difficult calvings will be influenced by the current mean level of calving difficulty • Most difficult calvings will occur in the bull calves born to heifers calving for the first time

15. Consider Stayability • RA4 had STY of 18 and RA5 was 8 • If mean stayability (fraction of first-calf heifers still in the herd at age 6) was 50% (about an average figure) and both bulls started with the same number of two yr olds then RA4 would have 10% more 6 yr old daughters

16. Stayability • The increased “longevity” or length of productive life of RA4 means his daughters need a smaller proportion of replacements allowing a greater fraction of heifer calves to be sold at weaning • Accordingly RA4’s daughters will have a smaller fraction of their total lifetime calvings as two-year olds

17. Multiplicative effects • RA4 will have less calving difficulty as over their lifetime his daughters have a smaller proportion of first calvings • RA4’s daughters will wean a greater weight of calf on average as they are typically older at calving and middle-aged cows wean heavier calves than first and second-calving cows

18. Consider Feed Requirements • The retained daughters (and steer and surplus heifer offspring) of these two bulls will consume different amounts of feed as they have different growth curves and therefore different requirements for growth and for maintenance, as well as different requirements for pregnancy (BW), lactation (WWM) and replacements

19. Ramifications • Determining the ramifications of using these two bulls within some system context accounting for all the differences in these traits is clearly problematic • It cannot be done without generating some kind of a “herd” and undertaking considerable arithmetic • Such computations could provide useful “decision support” and allow our bulls to be compared on some productive and economic basis

20. Index Selection • One form of decision support is to combine the set of EPDs on these bulls into some measure of aggregate economic merit • This requires deriving a (relative) economic value for each EPD • Partial derivative of some ranch profit function • Partial budget

21. Relative Economic Values • These economic values could then be used in product with the corresponding EPDs for each bull to give the value of each trait change and these could be accumulated to produce a single index value for selection • This has been done many times in the past with a few notable successes but generally relatively poor levels of adoption

22. Merit or Selection Index • These can simplify selection if they are accepted and used in place of the component EPDs • These can be counter productive • When they simply add more “EPDs” to be considered especially if several indexes are added • When they suggest “one size fits all”

23. Selection Now More Difficult • It has been argued that the addition of ever more EPD has made selection more difficult rather than more straightforward

24. Merit or Selection Index • Often the indexes have not been adopted because they don’t make sense to users • The weights are functions of some assumed “average” performance and future production and management circumstances • The weights are counter intuitive (or not disclosed) • This often occurs when the EPD used as selection criteria are not the same as the “traits” in the breeding objective

25. Selection Index • Selection Index principles (Pb=Gv) are used to determine index weights (ie b-values) for EPDs that are functions of economic weights in v and covariance parameters in G • Some weights can be non-zero even for EPDs that have no economic relevance

26. Economically Relevant Traits • The concept of ERTs aims to separate index construction (as far as possible) into two discrete parts • Part 1: Statistics. Use observations on indicator traits and economically relevant traits to derive EPDs for ERTs • Part 2: Economics. Use economic weights to combine ERTs into an index

27. Further Complications • Let’s suppose further that we wish to compare all three bulls but RA5 and RA4 are Red Angus bulls whereas LM5 is a Limousin bull • Our cow herd might be one of these two breeds, or perhaps something completely different

28. Base Adjustment • If these EPDs are published on a within-breed base, they cannot be compared without prior knowledge of the base adjustments • For some traits, these are regularly published by Dr Van Vleck and colleagues based on pure and crossbred performance at Clay Centre Nebraska • More knowledge and arithmetic !

29. Heterosis • The performance attributes we have considered to date will be influenced by direct and/or maternal heterosis • The coefficients of heterosis will be different according to the breed of our cow herd

30. Red Angus Herd • If our cows are Red Angus, there will be no heterosis when we use RA5 or RA4 in our herd • If we use LM5, then our offspring performance will include Limousin-Red Angus heterosis

31. Hereford Herd • If our herd is Hereford, then our future performance will be influenced by Hereford-Red Angus heterosis values if we use RA5 or RA4, but Hereford-Limousin heterosis if we use LM5 • Even more knowledge and arithmetic !

32. Selection by Simulation • An alternative approach to decision support is to show, by computer simulation via the web, at least some of the predicted herd outputs and inputs that would result if you actually used alternative bulls in some particular (or peculiar) production circumstance

33. Simulation • The simulation software should be linked to a database of national EPDs on candidate bulls • And (in future) to tables of heterosis values, and across-breed EPD adjustments (unless EPDs were from multibreed analyses)

34. Web Access to an “alpha” version ert.agsci.colostate.edu

35. Example Herd Production • 1,000 mixed age breeding cows • Weights at birth, weaning, yearling & maturity of 85, 500, 775 & 1,200 lb • 95% calf survival to weaning • 22% cows having their first calf experience calving difficulty • 90% mixed age cows survive and get pregnant to calve again next year

36. Example Herd Management • Feed is the limiting resource that dictates cow numbers • Determined by land area and rainfall • Cows are sold at 12 yr old • Daughters are retained as replacements

37. Example Herd Genetics • Cows are Red Angus • The herd EPDs are lagging two generations (10 years) behind the registered Red Angus population

38. Example Herd Economics • Incremental cow costs are $25 • Capital value of heifers, cows & bulls are $1,000, $800 and $2,000 • Disposal values of calves, heifers and cows are $100, $55 and $48 per cwt

39. Current Philosophical Approach Perturbed Situation Base Situation Current (equilibrium) Cow Herd (EPD & Performance) Like Merit Bulls X Base Cow-calf outputs & inputs

40. Base Herd

41. Sire Selector • Bulls can then be selected online from a database with the aid of sorting and filtering systems to identify animals of interest

42. Current Philosophical Approach Perturbed Situation Base Situation Current Cow Herd (EPD) Chosen Bulls X Current (equilibrium) Cow Herd (EPD & Performance) Like Merit Bulls Daughter (equilibrium) Cow Herd (EPD & Base mean Performance) X Base Cow-calf outputs & inputs

43. Current Philosophical Approach Perturbed Situation Base Situation Current Cow Herd (EPD) Chosen Bulls X Current (equilibrium) Cow Herd (EPD & Performance) Like Merit Bulls Daughter (equilibrium) Cow Herd (EPD & base mean Performance) Like Merit Bulls X X Perturbed Cow-calf outputs & inputs Base Cow-calf outputs & inputs

44. Base vs Perturbed • Allows demonstration of the ramifications of changing the genetic merit of a herd unencumbered with gene flow and discounting considerations • Simplifies comparison of herds with different feed requirements

45. RA4 and RA5 • RA5 would increase profit $240 per bull (30 cows) with no change in feed requirements (cow numbers) • RA4 would increase profit $1,276 per bull after reducing herd size by 37 cows to 963

46. Bottom line $ • Note these “bottom line” $ are not constructed from a linear index • although a linear index may approximate them • You can dig deeper and examine the relative herd structure (click on magnifying class) or deeper still to examine the calf crop as sold and retained

47. RA4 and RA5 • These bulls are actually bogus, creating the RA genetic means for 1985 and 2004 if the cow herd EPDs had been set to zero • Genetic trend is about $1000 in 20 years or $50 per year over 30 cows for this scenario

48. Bogus Bulls • Bogus bulls have been created for genetic means and for REVs • These bulls can be obtained by filtering on name for “Genetic” or “REV” • REV bulls are all zero EPD except for one trait • Genetic mean bulls are twice the breed-year EPD so when mated to zero EPD cows create a herd with the genetic mean EPD for that birth year

49. Base vs Perturbed • Comparing bottom lines for base vs perturbed herds may distort the relativity of traits that are expressed at different stages of the life cycle • Discounted Gene Flow to produce a Net Present Value (NPV) for each bull is currently being added to the model • Creating other complications of valuing the opportunity cost of feed

50. Discounted Gene Flow Current Cow Herd (EPD) Ylg hfrs 2yo Cows 4yo Cows 5yo Cows X X X X X And so on Intermediate Merit Calf Crop Future Merit Bulls Future Merit Bulls Future Merit Bulls Future Merit Bulls Chosen Bulls $ Net Present Value of Cow-calf outputs & inputs Discount Rate