Genetic terms explained
Changes in evaluations following the April 2025 genetic base change
Holstein bulls
TPI is an index developed by Holstein Association USA and is widely used to compare sires’ breeding values. It includes predicted transmitting ability for protein (PTA Protein): 19%; fat (PTA Fat): 19%; Feed Efficiency (FE): 8%; PTA Type: 8%; Udder Composite (UDC): 11%; Feet and Legs Composite (FLC): 6%; Productive Life (PL): 5%; health traits: -2%; Cow Livability: 3%; Somatic Cell Score (SCS): -4%; Fertility Index (FI): 13%; Daughter Calving Ease (DCE): -0.5%; and Daughter Stillbirth (DSB): -1.5%. The value 2845 is adjusted for periodic genetic base changes, allowing TPI values to be compared over time.
Feed Efficiency (FE) includes the individual feed costs of producing an additional pound of milk, milk fat and protein. It also takes account of maintenance costs, including bedding, housing and calving pens, which may be higher for larger cows. Cows that produce a lot of milk without consuming large amounts of feed receive a higher score.
Net Merit estimates the expected lifetime profit, in dollars, that an animal’s offspring will generate. It is calculated using production, udder health, longevity and body size traits.
A multi-trait selection index for Holstein and Jersey cattle. Its formulas include production, fertility, type, longevity and health traits, as well as polled test results.
The average production of a bull’s daughters over 305 days of lactation, expressed in kilograms (2.20462 lb = 1 kg).
Predicted transmitting ability for milk yield, which a sire passes genetically to its offspring. It is expressed in pounds and indicates the milk production of a bull’s daughters relative to their contemporaries. Contemporaries are all evaluated cows born in the USA in 2020.
The predicted quantity of protein, in pounds, produced by a bull’s daughters relative to their contemporaries.
This value is obtained by relating PTA Protein to PTA Milk and expressing it as a percentage.
The predicted quantity of fat, in pounds, produced by a bull’s daughters relative to their contemporaries.
This value is obtained by relating PTA Fat to PTA Milk and expressing it as a percentage.
The number of lactating daughters included in the evaluation of a sire.
The number of herds in which the sire’s evaluated daughters are milked.
The expected improvement in the type, or conformation, of a bull’s daughters relative to their contemporaries.
An udder evaluation expressed as a single calculated value, taking account of the effect of udder traits on longevity. Udder Composite includes udder depth (UD), fore udder attachment (FUA), rear udder height (RUH), rear udder width (RUW), udder cleft (UC), front teat placement (FTP), rear teat placement (RTP), teat length (TL) and stature (S). Intermediate values are optimal for rear teat placement and teat length.
UDC = [(0.16 x FUA) + (0.23 x RUH) + (0.19 x RUW) + (0.08 x UC) + (0.20 x UD) + (0.04 x FTP) + (0.05 x RTP*) + (0.05 x TL*) – (0.2 x S)] x 1.16
Combines three linear traits — foot angle, rear legs viewed from behind and rear legs viewed from the side — with the feet and legs score.
Body Size Composite is derived from the linear traits stature, strength, body depth, rump width and dairy form.
This measure is derived from linear evaluations of dairy form and strength.
This trait indicates the tendency towards difficult births among calves sired by a particular bull. Calving ease is expressed as the incidence of difficult births in first-calving heifers. For Holstein heifers whose sires were born in 2020, the incidence of difficult first calvings is approximately 1.36%. As this average approaches zero, variation in PTA has decreased. The low number of recorded difficult births naturally limits PTA values, since values below 0% are biologically impossible. This does not mean that SCE selection criteria should be neglected, but minimal differences between bulls in the population should not cause concern.
DCE indicates whether a sire’s daughters tend to have more or fewer difficult calvings than the breed average. It reflects a cow’s ability to calve easily. Easier calving in a sire’s daughters is associated with a higher Productive Life score.
A genetic measure of the number of months a cow produces milk while in the herd. No more than 305 days, or 10 months, per lactation are included in the calculation. A bull’s daughters can receive an evaluation only from 36 months of age and up to 7 years of age. Productive Life scores range from -7.0 to +7.0.
Somatic Cell Score is based on monthly tests of a bull’s daughters. The SCS index indicates their likelihood of developing mastitis. PTA SCS ranges from 2.50 to 3.50. Lower values are more desirable. The heritability of this trait is 10%, and the breed average is 3.00.
The Fertility Index combines three fertility evaluations to provide a comprehensive picture of fertility performance.
FI = (0.7 x DPR) + (0.1 x CCR) + (0.1 x HCR) + (0.1 x EFC)
HCR = PTA Heifer Conception Rate — measures the ability of a bull’s non-lactating daughters to conceive.
CCR = PTA Cow Conception Rate — measures the ability of a bull’s lactating daughters to conceive.
EFC = Early First Calving
DPR = PTA Daughter Pregnancy Rate — measures the ability of a bull’s daughters to resume cycling, show heat, conceive and maintain pregnancy. FI is calculated only for Holsteins. It replaces DPR in the TPI formula.
This measure indicates how quickly a cow resumes cycling and becomes pregnant after calving. PTA Daughter Pregnancy Rate ranges from +3.0 to -3.0, with higher values preferred. One percentage point is equivalent to 4 days: +1.0 indicates that a sire’s daughters have a calving-to-conception interval that is 4 days shorter, whereas -1.0 indicates an interval that is 4 days longer.
PTA Cow Livability indicates the percentage deviation in the survival of a bull’s daughters from the breed average. It reflects a bull’s ability to sire daughters that remain productive in the herd and generate income through slaughter rather than dying on the farm. Cow Livability values range from -5 to +5. Unlike Productive Life, which also predicts the number of productive days in the herd, Cow Livability considers both lactation income and the expected additional revenue from voluntary or involuntary slaughter.
Linear type evaluations
Genetic evaluations of linear type traits use multi-trait analysis. This improves evaluation accuracy by taking account of the genetic relationships between a particular trait and other linear traits.
Holstein Association USA provides genetic evaluations of linear type traits as Standard Transmitting Abilities (STAs). An STA expresses an animal’s genetic merit in standardised units relative to the average US cow born in 2020. Because bulls offered by artificial insemination organisations are carefully selected for production and type traits, these organisations’ bull populations have higher average STA values for most linear traits. >>Read more
| Abbreviation | Explanation |
|---|---|
| AG | Stature |
| PT | Dairy character |
| SP | Strength |
| KD | Body depth |
| KP | Rump width |
| KS | Rump angle |
| RLRV | Rear legs — rear view |
| RLSV | Rear legs — side view |
| FA | Foot angle |
| Feet and legs score | Feet and legs score |
| FUA | Fore udder attachment |
| RUH | Rear udder height |
| RUW | Rear udder width |
| UC | Udder cleft |
| UD | Udder depth |
| FTP | Front teat placement |
| RTP | Rear teat placement |
| TL | Teat length |
| SCS | Somatic Cell Score |
| TPI | Total Performance Index |
| PTA Protein | Predicted Transmitting Ability for Protein |
| PTA Fat | Predicted Transmitting Ability for Fat |
| PTA Type | Predicted Transmitting Ability for Type |
| NM$ | Net Merit |
| UDC | Udder Composite |
| AV | Calving Ease |
| DPR | Daughter Pregnancy Rate |
| DCE | Daughter Calving Ease |
| DSB | Daughter Stillbirth |
| SCR | Sire Conception Rate |
| SCE | Sire Calving Ease |
| SSB | Sire Stillbirth |
| SD | Days in milk |
Expected Progeny Differences, or EPD
Using Expected Progeny Differences (EPDs) is the fastest way to improve the genetics of beef cattle. Breed associations collect substantial amounts of data on different traits to document cattle’s genetic potential. The accuracy and impact of these data are considerable. Understanding sire summaries allows you to make mating decisions based on detailed records of individual traits and build a herd that suits your breeding programme.
A bull’s evaluation data can be compared only with data for other bulls of the same breed evaluated in the same country. The analysis accounts for differences within each herd in which animals are evaluated.
For example, bull A has a weaning weight EPD (WW) of +43, while bull B has a weaning weight EPD of +33. When these bulls are used in your herd, bull A’s calves can therefore be expected to weigh an average of 10 pounds more at weaning than bull B’s calves (43 – 33 = 10).
Expected progeny differences and profit indexes for an Angus bull (22.05.2025.)
The expected difference between a particular bull’s offspring and the average offspring of all evaluated bulls. EPDs should be used to compare bulls within a breed, rather than to predict actual performance. EPDs are breed-specific and cannot be used to compare sires of different breeds. They are generally expressed in the units of the relevant trait, such as pounds, cm, cm2 or percentages.
A measure of the reliability of a bull’s breeding value. Higher accuracy indicates more reliable data that are less likely to change in subsequent generations. Accuracy closer to 1.00 indicates greater reliability.
Indicates percentile ranking. In the example EPD table above, the animal’s $AxH index of 198 places it in the top 10% of the population for this index.
Expressed as a percentage difference in unassisted births among a bull’s calves born to first-calving heifers. Here, first-calving heifers are females that calve for the first time before 33 months of age. When comparing two sires’ CED values, a higher value indicates a greater percentage of unassisted births among that bull’s calves.
A calf’s birth weight adjusted to a mature-dam equivalent. Birth weight EPD is expressed in pounds and predicts the expected difference in the birth weight of a bull’s calves compared with those of other evaluated bulls. A positive value indicates a heavier-than-average birth weight; a negative value indicates a lower-than-average birth weight.
A sire’s EPD, in pounds, for calf weight at 205 days, adjusted to a mature-dam equivalent. It indicates weaning weight relative to the average for all evaluated bulls.
The EPD indicates the weight, in pounds, of a bull’s offspring at 365 days relative to the average for all evaluated bulls.
This EPD describes post-weaning feed efficiency in Angus cattle. RADG is expressed in pounds per day. Higher values offer a greater advantage to the breeder.
This EPD describes an Angus sire’s ability to transmit post-weaning feed intake to its offspring. DMI is expressed in pounds per day. Calves sired by a bull with a DMI EPD of 1.50 will consume approximately 0.5 lb more dry matter per day than calves sired by a bull with an EPD of 1.00.
For Angus cattle, this EPD predicts differences in the height of a bull’s offspring compared with those of other evaluated bulls. It is expressed in inches.
The EPD predicts differences in the scrotal circumference of a bull’s male offspring relative to the breed average.
The EPD is expressed as a genetic difference in percentage points. Higher values indicate a calmer temperament.
The EPD predicts genetic differences in claw structure, shape and uniformity. Lower values are preferred, indicating animals with symmetrical, even claws and appropriate spacing.
The EPD predicts genetic differences in foot angle, including pastern strength and heel depth. Lower values indicate animals expected to produce offspring with a more desirable 45-degree angle, appropriate toe length and heel depth.
This EPD is expressed in hair-shedding score units. Lower values are preferred and indicate that a sire is expected to produce offspring that shed their winter coat earlier in spring.
This EPD indicates the risk of high-altitude disease (HAD), which often causes heart failure. The trait is relevant to animals grazing at elevations above 1500 m.
Indicates the likelihood that a bull’s heifer daughters will become pregnant. The EPD is expressed as a genetic difference in percentage points; higher values are more favourable.
Expressed as a percentage difference in unassisted births. Higher values indicate easier first calvings for a bull’s daughters.
The EPD predicts differences in the weaning weight of calves born to a bull’s daughters at 205 days, attributable to their dams’ milk production, relative to calves from other evaluated sires. It is expressed in pounds.
The weaning weight of calves born to a bull’s daughters reflects both the daughters’ milk production and their calves’ growth potential. It is expressed in pounds.
The EPD predicts differences in the height of a bull’s daughters relative to the daughters of other evaluated sires. It is expressed in inches.
Expressed in dollars saved per cow per year, this index evaluates differences in the energy requirements of daughters of different sires. When comparing two animals, a higher value indicates greater savings in energy-dense feed costs. Calculating $EN savings for a cow considers her energy requirements throughout lactation and differences in feed costs associated with mature cow size.
Carcase evaluations
The EPD predicts differences in the hot carcase weight of a bull’s offspring relative to the offspring of other bulls. It is expressed in pounds.
The EPD is expressed as a fraction of a USDA marbling grade and indicates differences in the marbling of a bull’s offspring. Higher values indicate a higher marbling grade.
A measure of muscling in the carcase. The EPD predicts differences in ribeye area between a bull’s offspring and the offspring of other evaluated bulls. It is expressed in square inches.
The EPD predicts differences in fat thickness measured between the 12th and 13th ribs, comparing a bull’s offspring with those of other evaluated bulls. It is expressed in inches.
Profit indexes
$AxH and $AxJ are indexes designed to target calving ease, growth from birth through finishing, carcase yield and optimal muscling. Less emphasis is placed on marbling because dairy breeds already tend to produce well-marbled beef. $AxH places negative emphasis on YH to help reduce carcase length.
$AxH and $AxJ are indexes designed to target calving ease, growth from birth through finishing, carcase yield and optimal muscling. Less emphasis is placed on marbling because dairy breeds already tend to produce well-marbled beef. $AxH places negative emphasis on YH to help reduce carcase length.
An index expressed in US dollars per head that predicts average differences in the pre-weaning value of future offspring relative to offspring of other evaluated bulls. It incorporates revenue and cost adjustments for birth weight, weaning growth, maternal milk production and cow size.
An index expressed in US dollars per head that predicts average differences in the post-weaning value of offspring relative to offspring of other evaluated bulls.
An index expressed in US dollars per head that predicts average differences in carcase grid value for offspring relative to offspring of other evaluated bulls.
Based on genetic traits, this index predicts average differences in the profitability of offspring in terms of feed costs and carcase value relative to offspring of other sires. It includes post-weaning growth, carcase yield, marbling and efficiency traits.
Expressed in dollars per animal, Combined Value ($C) includes all 15 traits associated with $M and $B — the maternal and beef value indexes.