Individual Traits

U.S. evaluations measure genetic variation for 50 traits important to dairy producers. Nearly all U.S. traits are calculated and published by CDCB.

Most evaluations are expressed as Predicted Transmitting Abilities, or PTAs, which measure the difference an animal’s offspring is expected to exhibit when bred to a mate that represents the average merit of the population. Each PTA is usually expressed in the units used to measure the trait.

Selection indices combine many traits into a single value to rank animals. Indices simplify selection decisions and maximize overall genetic progress. The primary U.S. national selection index is Net Merit Dollars. Three other lifetime merit indices are available – Cheese Yield Dollars, Fluid Merit Dollars and Grazing Merit Dollars.

Production and Yield

PTA Milk predicts the expected milk production of future mature daughters, in pounds, in comparison to other cows of the breed born in the same base year. Below is the relative weight milk holds in the selection indices – represented by light blue.

PTA Fat predicts the expected milkfat production of future mature daughters, in pounds, in comparison to other cows of the breed born in the same base year. Below is the relative weight fat holds in the selection indices – represented by light blue.

Fat Percent predicts the animal’s genetic ability to transmit concentration of milkfat; expressed as percentage points in comparison to the breed base.

PTA Protein predicts the expected milk protein production of future mature daughters, in pounds, in comparison to other cows of the breed born in the same base year. Below is the relative weight protein holds in the selection indices – represented by light blue.

Protein Percent predicts the animal’s genetic ability to transmit concentration of milk protein; expressed as percentage points in comparison to the breed base.

Feed Efficiency

Feed Saved indicates the expected reduction of feed consumed each lactation based on evaluations for Residual Feed Intake and Body Weight Composite; measured in pounds of dry matter intake.

Residual Feed Intake (RFI) is a measure of feed efficiency and is defined as the difference between an animal’s actual feed intake and its expected feed intake based on its size and growth compared to the breed average base. RFI is independent of the level of production. The lower the RFI value, the more efficient the animal is. Below is the relative weight RFI holds in the selection indices – represented by light blue.

Longevity and Health

Somatic Cell Score (SCS) indicates genetic susceptibility for udder health, as revealed through somatic cell count. Animals with PTA SCS <3.0 are expected to transmit favorable udder health, while animals with PTA SCS >3.0 are expected to have daughters with cell counts higher than breed average. Below is the relative weight SCS holds in the selection indices – represented by light blue.

Productive Life predicts the time that female offspring are expected to remain in milking herd before removal by culling or death; expressed as difference in months of productivity compared to the breed base. Below is the relative weight Productive Life holds in the selection indices – represented by light blue.

Cow Livability predicts the difference in female offspring expected to remain alive while in the milking herd; expressed in percentage points from the breed base.

Heifer Livability predicts the difference in female young offspring expected to remain alive between 2 days after birth and 18 months of age; expressed in percentage points from the breed base.

Gestation Length is the expected influence the animal will have on the days that their female offspring carry their calves, compared to the breed average base.

Expected resistance of an animal’s offspring to displaced abomasum compared to the breed average base, expressed in percentage points.

Expected resistance of an animal’s offspring to hypocalcemia (milk fever) compared to the breed average base, expressed in percentage points.

Expected resistance of an animal’s offspring to ketosis compared to the breed average base, expressed in percentage points.

Expected resistance of an animal’s offspring to clinical mastitis compared to the breed average base, expressed in percentage points.

Expected resistance of an animal’s offspring to metritis compared to the breed average base, expressed in percentage points.

Expected resistance of an animal’s offspring to retained placenta compared to the breed average base, expressed in percentage points.

Fertility and Calving

Sire Conception Rate is a male fertility trait that predicts future differences in conception rates of service sires, as percentage points deviation from the average of the breeds’ A.I. bulls.

Cow Conception Rate is a female fertility trait predicting the lactating cow’s ability to conceive, defined as expected percentage to become pregnant at each insemination in comparison to the breed base.

Heifer Conception Rate is a female fertility trait predicting the maiden heifer’s ability to conceive, defined as expected percentage to become pregnant at each insemination in comparison to the breed base.

Daughter Pregnancy Rate is a female fertility trait that predicts the percentage of non-pregnant cows that will become pregnant during each 21-day period compared to the breed base.

Sire Calving Ease predicts the tendency of service sires to produce offspring that are delivered easily, expressed as percentage of births of bull calves coded difficult for first calf (primiparous) heifers compared to other A.I. bulls born in 2015.

Daughter Calving Ease predicts the tendency of the daughters of sires to have offspring that are delivered easily, expressed as percentage of births of bull calves that are difficult in first calf (primiparous) heifers compared to other A.I. bulls born in 2010.

Sire Stillbirth predicts the tendency of service sires to produce offspring that are stillborn (dead at birth or within 48 hours of birth), expressed as percent compared to other A.I. bulls born between 2011 and 2015.

Daughter Stillbirth predicts the tendency of the daughters of sires to have offspring that are stillborn (dead at birth or within 48 hours of birth), expressed as percent compared to other A.I. bulls born between 2006 and 2010.

Early First Calving indicates the animal’s genetic ability to alter their female offspring’s age at first calving, defined in days compared to the breed base.

Conformation and Type

PTA Type Predicts the animal’s genetic ability to transmit to the offspring’s final classification or appraisal score in the breed’s program. Published by breed association.

Udder Composite is an index that combines several udder traits, weighting the linear traits in the index by their economic benefit. Published by breed association.

Feet and Legs Composite is an index that combines several feet and leg traits, weighting the linear traits in the index by their economic benefit. Published by breed association.

Body Weight Composite is an index of body size (dimensions of the cow) and dairy form, weighting the linear traits in the index by their economic benefit. Published by breed association.

The18 linear type traits are expressed as Standard Transmitting Abilities (STAs) in the Holstein breed and as a percentage point deviation in the other breeds. For non-Holstein breeds, calculated by CDCB and based on breed association type appraisal data. Holstein evaluations are calculated by their own breed association.