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An animal’s breeding value is its genetic merit, half of which will be passed on to its progeny. While we will never know the exact breeding value, for performance traits it is possible to make good estimates. These estimates are called Estimated Breeding Values (EBVs).

EBVs are expressed in the units of measurement for each particular trait. They are shown as + ive or – ive differences between an individual animal’s genetics difference and the genetic base to which the animal is compared. For example, a bull with an EBV of +50kg for 600-day weight is estimated to have genetic merit 50kg above the breed base of 0kg. Since the breed base is set to an historical benchmark, the average EBVs of animals in each year drop has changed over time as a result of genetic progress within the breed.

The absolute value of any EBV is not critical, but rather the differences in EBVs between animals. Particular animals should be viewed as being “above or below breed average” for a particular trait.

While EBVs provide the best basis for comparing the genetic merit of animals reared in different environments and management conditions, they can only be used to compare animals analysed within the same analysis.

Simmental NZ animals EBVs can be compared to any other animals within the IGS evaluation, this included other breeds.

MATERNAL EBVS

CALVING EASE DIRECT (CE-D)
Reported as the percentage of extra unassisted births in first calving heifers, relative to the average. CE-D is relative to the direct Calving Ease of the animal. Higher values are more favourable.

CALVING EASE MATERNAL (CE-M)
Reported as the percentage of extra unassisted births in first calving heifers, relative to the average. CE-M is relative to the Calving Ease of the daughters of the animal. Higher values are more favourable.

GESTATION LENGTH
(days) is an estimate of the time from conception to the birth of the calf and is based on artificial insemination and hand mating records. Lower (negative) Gestation Length EBVs indicate shorter gestation length and easier calving and increased growth after birth.

MILK
Reported as kilograms of weaning weight of progeny from the animals daughters, relative to the average. Predicts the difference in maternal production of daughters relative to milk production and mothering. Values are relative to the environment of the production system. Low input environments should be very consious of introducing too much milk due to the increased nutrient requirements that it can place on cows.

MATERNAL WEANING WEIGHT
Reported as kilograms of weaning weight of progeny from the animals daughters, relative to the average. This is a measure of weaning weight differences relative to the combined effects of growth and milk. Breeders who are not looking to change milk production should consider Total Maternal as the most relevant EBV for maternal weaning weights. Higher values are more favourable.

STAYABILITY (STAY)
Reported as the differences in percentage of a sire’s offspring that are predicted to still be in the herd at 6 years of age, given that they calved at 2, relative to the average. Stayability is a measure of reproductive longevity. Higher values are more favourable.

DOCILITY
Reported as the percentage of progeny, relative to the average, that will record a score of docile.
Higher values are more favourable.

GROWTH EBV’S

BIRTH WEIGHT
Reported in kilograms of birth weight relative to the average.
When selecting bulls to use on heifers, breeders should also focus on the Calving Ease EBV as Birthweight is already used in the Calving Ease EBV calculation.

WEANING WEIGHT – ADJUSTED TO 205 DAYS
Reported in kilograms of weaning weight of direct progeny, relative to the average.
Higher values are usually more favourable dependant on its relationship with birthweight.

YEARLING WEIGHT – ADJUSTED TO 365 DAYS
Reported in kilograms of yearling weight of direct progeny, relative to the average.
Higher values are usually more favourable dependant on its relationship with birthweight.

600- DAY WEIGHT (kg) is calculated from the weight of progeny taken between 501 and 900 days of age, adjusted to 600 days and for age of dam. This EBV is the best single estimate of an animal’s genetic merit for growth beyond yearling age.

CARCASE EBV’S – ADJUSTED TO 475 DAYS OF AGE.

CARCASE WEIGHT
Reported as kilograms of Carcase Weight relative to the average. Higher values are usually more favourable, however this is relevant to each producers target market.

RIB EYE AREA
Reported as square inches relative to the average. Higher values are usually more favourable.

FAT
Reported as inches of back fat relative to the average. Higher values are usually more favourable, however this is requires a balance between adequate doing ability in daughters and carcase fat thresholds for target markets.

MARBLE SCORE
Reported as the differences in actual carcase marble scores relative to the average. This is different to IMF% which is used as an indicator trait in Marble Score. Higher values are more favourable.

New Zealand Simmental selection indexes are calculated for two market specifications – Maternal (Self Replacing) and Terminal. These Indexes relate to typical commercial herds in temperate New Zealand targeting these specifications.

Indexes are reported as an EBV, in units of relative earning capacity ($’s) for a given market. They reflect both the short-term profit generated by a sire through the sale of his progeny, and the longer-term profit generated by his daughters in a sustainable cow herd, if a proportion of heifers are retained for breeding.

The Indexes are derived using BreedObject technology. More information on this technology is available from BreedObject.

ALL PURPOSE INDEX – API

The All Purpose Index (API) evaluates sires for use on the entire cow herd, bred to both first-calf heifers and mature cows, with the portion of their daughters required to maintain herd size retained and the remaining heifers and steers put onto feed and marketed for both quality grade and yield.

TERMINAL INDEX – TI

Evaluates sire for use on mature cows with all offspring put on feed and sold grade and yield.

Both heifer and steer progeny are pasture grown and finished and are slaughtered to produce a 300kg carcass at 15 months. All progeny are slaughtered. More information is available on the EBV weightings and profit drivers for the Terminal Index.

Note that $Index Values for individual animals are sensitive to the assumptions used in the BreedObject analysis to calculate the relevant selection index.

UNDERSTANDING ACCURACIES
BOLT EBV accuracies have experienced the most change, usually lowering numerically and especially for non-parent animals, however the reported accuracy will be more accurate.
Accuracy refers to the amount a reported EBV can possibly change as more data is added. EBV values with higher accuracy result in less possible change for the value over time. More accurate accuracies better represent the amount of possible change for each EBV.

Accuracy range	Interpretation
less than 50%	Low accuracy. EBVs are preliminary and could change substantially as more performance information becomes available.
50-74%	Medium accuracy, usually based on the animal’s own records and pedigree.
75-90%	Medium-high accuracy. Some progeny information included. EBVs may change with addition of more progeny data.
more than 90%	High accuracy estimate of the animal’s true breeding value.

As a rule, animals should be compared on EBVs regardless of accuracy. However, where two animals have similar EBVs the one with higher accuracy could be the safer choice, assuming other factors are equal.

For more information contact the New Zealand Simmental Association.