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
NLPF		4	Number of litters per female
CNPD		1.90	Cost of nonproductive sow days
RBMP		$.62	Base market price/lb live weight for a 48% fat-free lean carcass
RLFCST		$.19	Labor and facilities cost/day
RFDCST		$.12	Feed cost/lb of feed
ZMNDX		$38.57	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		$38.57	Value of a pig at weaning
VPB		$28.28	Value of a pig at birth
CPB		$.35	Cost to process newborn pig
CLD		$2.75	Cost/day for sow in farrowing and lactation
CLW		$.06	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		24.88	Average PWI with zero EPDs
ZPWIMAT		6.928	Average PWIMAT
ZSPI		182.18	Constant for SPI (used so SPI will average 100)
ZMLI		157.06	Constant for MLI (used so MLI will average 100)
ZTSI		-237.15	Constant for TSI (used so TSI 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 = -21.896*BACK + 3.005*LEA

FUG = .0146*DAYS - .02083*LBLEAN

For a maternal line, ZLBLEAN = 94
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 = 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 )
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] * (DWTB * CNPD)–ZSPI

PWI = PIGVALTS-RLFCST*(ZDAYS+DAYS)
            -WTGAIN*RFDCST*(ZFUG+FUG)-(ZMNDX+ZPWI)

TSI = (PWI+10.)*10. - ZTSI

PWIMAT = PIGVALML-RLFCST*(ZDAYS+DAYS)
            -WTGAIN*RFDCST*(ZFUG+FUG)-(ZMNDX+ZPWIMAT)

MLI = (XSTWNM+NW)*(ZMNDX+.5*PWIMAT)+(VPB-CPB)*NBA
            -(DWBAR+DW)*(CLD+CLW*(XSTWNM+NW)
            -[(NLPF-1)/NLPF] * (DWTB * CNPD)-ZMLI

With current mean of 50 for NPD, 21 d weaning and other means:
Litters per sow per year = [(365 – (50 + (2.3333 x DWTB))]/ 135
p/s/yr = [( 10.4 + NBA )( 1- .11) +  NW  ] x litters/sow/year