1 Ramifications of Selection Decision Support for Cow-Calf Improvement [email protected]

11

Ramifications of Selection Ramifications of Selection Decision Support Decision Support

for Cow-Calf Improvementfor Cow-Calf Improvement

[email protected]@Colostate.edu

22

The Selection ProblemThe 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

33

Informed DecisionsInformed Decisions

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

44

Example BullsExample Bulls

Bull BW WWD YW WWM CED HPG CETM STY ME

RA4 1 56 98 30 8 20 8 18 0

RA5 -1 28 38 8 10 16 4 8 4

LM5 7 79 106 16 4 - 5 10 -

55

Consider WWD EPDsConsider 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

66

Consider WWD & WWM EPDsConsider 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

77

Consider HPG EPDConsider 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

88

Number of daughtersNumber 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

99

Underlying Scores to Preg RateUnderlying Scores to Preg Rate

20%

Truncn pt = 0.84

Heifers not in calfPregnant Heifers

1010


0.38

20%

Truncn pt = 0.84


1111


0.38Phenotypic s.d. = 1.17

20%

Truncn pt = 0.84

Truncn pt = 0.84 +0.38/1.17=1.165

12%


1212


0.38Phenotypic s.d. = 1.17

10%

Truncn pt = 1.28

Truncn pt = 1.28 +0.38/1.17=1.605

5.5%

1313

Sensitive to the AverageSensitive 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%

1414

Consider CED and CETMConsider 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

1515

Consider StayabilityConsider 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

1616

StayabilityStayability

• 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

1717

Multiplicative effectsMultiplicative 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

1818

Consider Feed RequirementsConsider 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

1919

RamificationsRamifications

• 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

2020

Index SelectionIndex 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

2121

Relative Economic ValuesRelative 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

2222

Merit or Selection IndexMerit 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”

2323

Selection Now More DifficultSelection Now More Difficult

• It has been argued that the addition of ever more EPD has made selection more difficult rather than more straightforward

2424

Merit or Selection IndexMerit 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

2525

Selection IndexSelection 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

2626

Economically Relevant TraitsEconomically 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

2727

Further ComplicationsFurther 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

2828

Base AdjustmentBase 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 !

2929

HeterosisHeterosis

• 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

3030

Red Angus HerdRed 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

3131

Hereford HerdHereford 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 !

3232

Selection by SimulationSelection 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

3333

SimulationSimulation

• 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)

3434

Web Access to an “alpha” versionWeb Access to an “alpha” version

ert.agsci.colostate.edu

3535

Example Herd ProductionExample 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

3636

Example Herd ManagementExample 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

3737

Example Herd GeneticsExample Herd Genetics

• Cows are Red Angus

• The herd EPDs are lagging two generations (10 years) behind the registered Red Angus population

3838

Example Herd EconomicsExample 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

3939

Current Philosophical ApproachCurrent Philosophical Approach

Current(equilibrium)

CowHerd(EPD

&Performance)

LikeMeritBulls

Base Cow-calf outputs & inputs

Base Situation Perturbed Situation

X

4040

Base HerdBase Herd

Nos Cap Val

Income

Expenses

Calves 935 $139,056 $302,633 $7,348

Yrlgs 296 $295,837

2 yr olds 281 $224,836 $7,945 $5,917

3 yr olds 253 $202,353 $48,763 $25,000

4 yr olds 228 $182,117

5 yr olds 154 $122,929

6 yr olds 69 $55,318

7 yr olds 16 $12,447

Total 1,000 $1,095,837 $359,341 $38,264

4141

Sire SelectorSire Selector

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

4242



CowHerd(EPD

&Performance)

LikeMeritBulls



CurrentCowHerd

(EPD)

ChosenBulls

Daughter(equilibrium)

CowHerd(EPD

& Base meanPerformance)

X

X

4343



CowHerd(EPD

&Performance)

LikeMeritBulls



CurrentCowHerd

(EPD)

ChosenBulls

Daughter(equilibrium)

CowHerd(EPD

& base meanPerformance)

LikeMeritBulls

Perturbed Cow-calf outputs & inputs

X

X

X

4444

Base vs PerturbedBase 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

4545

RA4 and RA5RA4 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

4646

Bottom line $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

4747

RA4 and RA5RA4 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

4848

Bogus BullsBogus 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

4949

Base vs PerturbedBase 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

5050

Discounted Gene FlowDiscounted Gene FlowCurrent

CowHerd

(EPD)

ChosenBulls Intermediate

MeritCalf Crop

FutureMeritBulls

$ Net Present Valueof Cow-calf outputs & inputs

X X

Ylghfrs

2yoCows

4yoCows

5yoCows

FutureMeritBulls

FutureMeritBulls

FutureMeritBulls

X X X And so on

Discount Rate

5151

Current EnhancementsCurrent Enhancements

• Adding other sire breeds for within-breed use– Braford, Limousin, Red Angus, Salers,

Simmental, South Devon (and individual breeders)

• Accounting for risk associated with variation in the accuracy of EPDs– Distribution of $ value for each sire rather

than just a mean $value for each sire

5252

ImprovementsImprovements

• The prototype exists so users can communicate the parts they like, the parts they don’t like and suggestions for things we can do differently (better)– Please report any “bugs” you find to me

(via email)

• Welcome involvement from other researchers who want to be part of our decision support team

Documents

1 Ramifications of Selection Decision Support for Cow-Calf Improvement [email protected]