Glossary of terms

Accuracy
Accuracy is expressed as a percentage and measures how well the EBV reflects the true breeding value. An EBV estimated with an accuracy of 99% would be unlikely to change with more information from relatives compared to an EBV with a low accuracy of 30%. An EBV with a low accuracy does not indicate whether the EBV is likely to rise or fall in future evaluations. When selecting animals for replacement it is better to select animals with the highest EBVs to increase the chances of maximum response. Animals with a higher accuracy, however, may be selected when comparing animals with similar EBVs in order to reduce risk.
Active animals
Are defined as animals under 200 days of age or flagged as active in the PIGBLUP data file.
Backfat (Fat)
Backfat depth (mm) is the measurement at the P2 position. Animals with the largest negative EBVs for this trait are those with the lower backfat.
Base year
All EBVs are compared with a historical benchmark. EBVs of animals listed on this site represent the change in average genetic merit since 1991.
Daily Gain (DG)
Lifetime daily weight gain (grams) from birth to finish.
Economic Index
An economic index is the sum of the EBVs for individual traits multiplied by the economic value of that trait. The economic value of a trait is the change in profit observed when that trait is changed by one unit and all others factors affecting performance are kept constant.
Estimated breeding values (EBVs)
An animal's EBV reflects its own genetic merit, of which half is passed on to his/her offspring. Progeny performance can be predicted by averaging the EBVs of both parents.
Linkage
Herd linkage is an essential component of across-herd evaluations. Herds that share sufficient common genes (eg through AI) can be corrected for differences in production environments to reveal true genetic differences between batches of animals in different herds.
Participating NPIP herds can improve across-herd linkage by measuring common traits in offspring from the same AI animals used by other NPIP herds. Performance testing offspring from live animal introductions from other NPIP herds is another method of improving linkage. To improve linkage for number born alive, daughters from those AI sires should be selected as sows. Linkage information is generated when number born alive is recorded from their litters.
Number Born Alive (NBA)
Additional pigs born alive per litter. Herds are poorly linked for this trait, making it difficult for accurate comparisons between herds. This does not mean that significant genetic gains have not been made in improving live birth in different herds.
Percentiles
The distribution of breeding values in a population are shown by the percentile tables. They were determined from genetic merit of all pigs performance tested over the last 12 months. They can be used to determine the percentage ranking of individuals compared to the current population. A daily gain of 45g/day in the 10% percentile means that 10% of animals have a daily gain greater than 45g/day and 90% of animals have a daily gain lower than 45g/day.