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Formulas for STAGES Indexes
Revised October 2005
Traits in the postweaning analysis are Days to 250 lbs, Backfat, and Loin Eye Area. Traits in the reproductive analysis are Number born alive, Number weaned (number at 21 days), and Litter weight at 21 days. Other EPDs are calculated from these.
STAGES indexes are economic indexes. EPDs are combined with the economic values to calculate the indexes. A constant is added to the indexes so they will average 100.
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First, here are the names of the EPDs and Indexes, and the Economic Values currently being used.
EPDs:
DAYS
Days to 250 lbs
BACK
Backfat, in.
LEA
Loin Eye Area, in2
LBLEAN
Pounds of Fat-Free Lean adjusted to a 250 lb live weight
FUG
Feed/lb of gain
NBA
Number Born Alive
NW
Number Weaned
LW
Litter Weight at 21 days, lbs
LBW
Litter Birth Weight, lbs
DW
Days to Weaning ( to reach a specific target BW )
DWTB
Days from Weaning to Breeding
MBW
Mean birth weight ,lbs
Indexes:
PWI
PostWeaning Index for a terminal sire line
PWIMAT
PostWeaning Index for a maternal line
TSI
Terminal Sire Index
MLI
Maternal Line Index
SPI
Sow Productivity Index
Economic Values and Constants:
NLPF
4
Number of litters per female
CNPD
1.65
Cost of nonproductive sow days
RBMP
$.45
Base market price/lb live weight for a 48% fat-free lean carcass
RLFCST
$.17
Labor and facilities cost/day
RFDCST
$.07
Feed cost/lb of feed
ZMNDX
$30.00
Value of a pig at weaning
SLWT
265
Target slaughter weight (lbs)
WTGAIN
250
Weight gained from weaning to slaughter
ZDAYS
170
Average days to 250 lbs
ZFUG
3.25
Average feed/lb gain (lbs)
VPW
$30.00
Value of a pig at weaning
VPB
$22.00
Value of a pig at birth
CPB
$.35
Cost to process newborn pig
CLD
$2.00
Cost/day for sow in farrowing and lactation
CLW
$.035
Extra feed cost/pig
DWBAR
22.637
Average days to weaning (15 lb pigs weaned)
XST
10.4
Average size of standardized litter
WNM
.11
Average preweaning mortality
XSTWNM
9.256
XST(1-WNM) = Average litter size at weaning
TWW
15
Target weaning weight (lbs)
XBW
3.2
Average birth weight (lbs)
ZLW
130.94
Average litter weight at 21 days (lbs)
ZPWI
4.80
Average PWI
ZPWIMAT
6.928
Average PWIMAT
ZSPI
66.48
Constant for SPI (used so SPI will average 100)
ZMLI
66.48
Constant for MLI (used so MLI will average 100)
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Formulas used:
Let:
ZLBLEAN
Average pounds of lean
VALITS
Value index for terminal sire line
VALIML
Value index for maternal line
PIGVALTS
Value of a pig at 265 lbs for a terminal sire line
PIGVALML
Value of a pig at 265 lbs for a maternal line
X and VI
Intermediate variables
Postweaning EPDs output from the analysis are DAYS, BACK, and LEA. Then:
LBLEAN = -14.95*BACK + 1.5*LEA
FUG = .0146*DAYS - .02083*LBLEAN
For a maternal line, ZLBLEAN = 92
X = ZLBLEAN+LBLEAN
If X 94 then X = 94.
If X 76.2 then VI = .918507 + .0068621*(X-76.2)
If X > 76.2 then VI = 3.433454 - (.112831*X) + (.001572*X2 ) - (.000006882*X3 )
VALIML = VI*1.0324
For a terminal sire line, ZLBLEAN = 87
X = ZLBLEAN+LBLEAN
If X 94 then X = 94.
If X 76.2 then VI = .918507 + .0068621*(X-76.2)
If X > 76.2 then VI = 3.433454 - (.112831*X) + (.001572*X2 ) - (.000006882*X3 )
VALITS = VI*1.0324
PIGVALTS = SLWT*RBMP*VALITS
PIGVALML = SLWT*RBMP*VALIML
Reproductive EPDs output from the analysis are NBA, NW, LBW, DWTB, and LW. Then:
MBW = ((33.28 + LBW+ 2.5 NBA)/(XST + NBA)- XBW
NW = NW + .77 *MBW
DW = [(XSTWNM+NW)*21.*(TWW-(XBW+2.2*MBW))/(ZLW+LW-(XSTWNM+NW)*(MBW+XBW))]-DWBAR
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Indexes are:
SPI = (XSTWNM+NW)*VPW+(VPB-CPB)*NBA
-(DWBAR+DW)*(CLD+CLW*(XSTWNM+NW))
-[(NLPF-1)/NLPF] x (DWTB x CNPD) |
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