Formulas for STAGES Indexes

Revised October 2006

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.

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	24.88	Average PWI with zero EPDs
ZPWIMAT	6.928	Average PWIMAT
ZSPI	66.48	Constant for SPI (used so SPI will average 100)
ZMLI	38.35	Constant for MLI (used so MLI will average 100)

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

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.

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

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