Country (or countries)

United States of America

Main trait group¹

Direct (single-trait) and combined (multi-trait) longevity.

Breed(s)

BSW, GUE, JER, HOL (B&W and R&W), MSH, RDC

All breeds and crossbred cows are evaluated together in a multi-breed animal model

Trait definition(s) and unit(s) of measurement²
Attach an appendix if needed

Productive life: Time in the milking herd before removal by voluntary culling, involuntary culling, or death. Credits for each month in milk are obtained from standard lactation curves and are then summed across all lactations. Diminishing credits within lactation give cows more credit for beginning a new lactation than for continuing to milk in the previous lactation.  Cows get 8 months credit for 305-d first lactation records, 10 months credit for second lactations, 10.2 months credit for third and later lactations, partial credits for shorter records, and extra credits for longer records.

Method of measuring and collecting data

Calving dates, disposal dates, reasons for disposal, and lactation lengths are obtained from DHI data. Dead cows receive credit for months of production as stated above. Live cows receive additional credit for predicted remaining life expectancy. Prediction factors consider the cow's age and stage of lactation. Credits from more than one herd are combined for cows that change herds. Published productive life combines information from direct longevity with evaluations from correlated traits.

Time period for data inclusion

Birth year 1950 and later for pedigree, 1960 and later for first calving. Cows must be born at least 3 years prior to the evaluation to be included.

Age groups (e.g. parities) included

All parities.

Other criteria (data edits) for inclusion of records

Cows must be sire identified with first lactation records.

Criteria for extension of records (if applicable)

Records are extended for cows that are still alive, were sold for dairy purposes, or were in herds that discontinued testing. Cows sold for dairy purposes or in herds that discontinued testing receive extended records if they had opportunity to reach 3 years of age; otherwise their records are discarded.

Sire categories

All sires (AI and natural service) are evaluated together.

Environmental effects³, pre-adjustments

Genetic variance in censored and uncensored management groups is equalized by pre-adjusting censored data using expansion factors.

Method (model) of genetic evaluation³

Single-trait BLUP animal model. Records from censored management groups receive less weight than from uncensored.

Environmental effects³ in the genetic evaluation model

Fixed: management group (flexible-length groups are based on herd of first lactation and birth date. Registry status is also considered for Holsteins only), regression on inbreeding. This model produces PTA adjusted to 0 inbreeding, but published PTA include the regressions multiplied by expected future inbreeding (EFI) and coefficients of heterosis when mated to purebreds as a post-processing step.

Random: Sire-by-herd interaction (variance = 5% of phenotypic variance).

Adjustment for heterogeneous variance in evaluation model

None.

Use of genetic groups and relationships

Unknown parents are grouped by year, breed, and, for Holsteins, separately for U.S. and foreign animals. Unknown sires and dams of cows are grouped separately, but unknown parents of bulls are in a combined group. Separate unknown parent groups are used for red and white or black and white Holsteins. The relationship matrix accounts for effects of inbreeding on Mendelian sampling variance.

Blending of foreign/Interbull information in evaluation

Direct longevity for foreign bulls is combined with PTA for other traits using the same multi-trait procedures used for domestic bulls.

Genetic parameters in the evaluation

Heritability is 8%. After the direct longevity evaluation, information from 9 other traits and composites is combined by selection index theory to increase PL reliability. These traits include yield, somatic cell score (SCS), daughter pregnancy rate (DPR), calving ability (CA$), and three conformation composites.
Correlations with PL are:
Milk .08
Fat .08
Protein .10
SCS -.38
DPR .51
CA$ .40
Composites:
Udder .30
Feet & leg .19
Size -.16
The selection index procedures use the predicted transmitting abilities, parent averages, and reliabilities of PTA and PA for the 10 traits and are applied to both bulls and cows in age order so that improved PL evaluations of parents are transferred to their progeny.

System validation

Direct PL is obtained with the same animal model programs used for yield. Combined PL programs produced evaluations similar to MACE when tested on international yield data. Trend validation methods 2 and 3 are applied separately to each breed.

Expression of genetic evaluations
If standardised (e.g. RBV), give standardisation formula in the appendix

PTA PL months

All-breed PTAs are adjusted to within-breed bases as follows:

within-breed PTA = (all-breed PTA – breed mean)

Definition of genetic reference base

Next base change

Five year stepwise base: average of all cows born in 2000 is set to 0.
Next base change in February 2010, when the base will be cows born in 2005.

Calculation of reliability

A daughter that has had the opportunity to reach 8 years of age is considered a completed observation and gets 1 daughter equivalent. Cows with less opportunity get less DE regardless of whether they are culled or alive. The DE are .22 at 36 months of age, .53 at 48 mo, .75 at 60 mo,  .89 at 72 mo, and .95 at 84 mo. These DE are combined with DE from parent average to calculate direct REL, and then DE from other traits increase the combined REL.

Criteria for official publication of evaluations

All bulls evaluated for milk yield by USA or by Interbull have official PL evaluations. Interbull longevity evaluations are used if the bull has foreign daughters and if the Interbull reliability is higher than the single-trait domestic longevity evaluation.

Number of evaluations / publications per year

Three, in February, May, and August of 2007, and in January, April, and August beginning 2008.

Use in total merit index⁴

Net Merit (all breeds): PL receives 17% of the total emphasis. TPI (Holsteins): PL receives 8% of the total emphasis.

Anticipated changes in the near future

None.

Key reference on methodology applied

· VanRaden, P.M. 2001. Methods to combine estimated breeding values obtained from separate sources. J.Dairy Sci. 84:E47.

· VanRaden, P.M., C.M.B. Dematawewa, R.E. Pearson, and M.E. Tooker. 2006. Productive life including all lactations and longer lactations with diminishing credits. J.Dairy Sci. 89:3213.

· VanRaden, P.M., and E.J.H. Klaaskate. 1993. Genetic evaluation of length of productive life including predicted longevity of live cows. J. Dairy Sci. 76:2758.

· VanRaden, P.M., M.E. Tooker, J.B. Cole, G.R. Wiggans, and J.H. Megonigal, Jr. 2007. Genetic evaluations for mixed-breed populations. J. Dairy Sci. 90:2434.

Key organisation: name, address, phone, fax, e-mail, web site

Animal Improvement Programs Laboratory
USDA, Agricultural Research Service
Building 005, Room 306, BARC-West
10300 Baltimore Avenue Beltsville, Maryland 20705-2350 U.S.A.

Tel: 301-504-8334 Fax: 301-504-8092
E-mail: paul@aipl.arsusda.gov
web site: http://aipl.arsusda.gov

Country (or countries):

Main trait group:

Longevity

Breed(s):

Trait

h²

genetic

variance

official proof

standardisation formula^a

Direct longevity:

.08

(5.04)²

Breed means for converting from the all-breed base to the within-breed bases will be updated on the AIPL web site. March 2007 estimates were:

BSW PTA = all-breed PTA – 0.3

GUE PTA = all-breed PTA + 4.3

HOL PTA = all-breed PTA + 0.1

JER PTA = all-breed PTA – 1.5

MSH PTA = all-breed PTA – 1.0

RDC PTA = all-breed PTA – 0.0

Combined longevity:

.08

(5.04)²

Same as above