Toelichting Signet Index & EBV

EBVs predict the genetic merit that an animal possesses for an individual trait or characteristic. Traits for which EBVs are calculated include 8 week weight of lambs; 21 week weight of lambs; muscle depth; fat depth; mature size; litter size; and maternal ability.
EBVs are produced using information recorded about their sheep by members of the group breeding schemes. They are calculated by computer using a programme that disentangles the complex relationship between the environment (feeding; management etc.) and the genetics of an individual animal. In this way, EBVs are able to provide considerable extra information about an animal compared to selecting ‘by eye’ alone. Nearly all dairy farmers select their animals using genetic information produced in a similar way. The production of EBVs by Flockbook.org members allows sheep farmers a similar advantage. To help identify superior animals, EBVs for a range of traits are also combined into a single breeding index. Please note that EBVs and breeding indexes can not be compared across different breeds.

8-Week weight EBV
This is a measure of the animal's genetic potential for growth from birth to weaning at
8 weeks.
A ram with an EBV of +3 for 8-week weight is expected to produce lambs which, on average, are 1.5 kg heavier at weaning compared to lambs sired by a ram with an EBV of 0.

21-week (Scan weight) EBV
This is a measure of the animal’s genetic potential for growth from birth to 21 weeks of age (age at scanning). Selection for high scan weights results in animals that will have heavier carcases at a constant fat class or leaner carcases at a constant age.
A ram with an EBV of +4 for scan weight is expected to produce, on average, lambs
2 kg heavier at 21 weeks than lambs sired by a ram with an EBV for this trait of 0.

Muscle depth EBV
This is a assessment of loin muscle depth and therefore likely lean meat yield.
A ram with an EBV of +1 for muscle depth is expected to produce, on average, lambs with 0.5 mm greater eye muscle depth at 21 weeks compared to lambs sired by a ram with an EBV of 0.

Fat depth EBV
Negative values indicate animals with lower fat levels, which will produce leaner carcases or which can be taken to heavier weights without becoming over-fat.
A ram with an EBV of -1.0 for fat depth is expected to produce, on average, lambs at 21 weeks with a subcutaneous fat thickness 0.5 mm less than lambs sired by a ram with an EBV of 0.
Maternal Traits
Many traits are expressed by both sexes (e.g. growth rate and muscling), but maternal traits (e.g. litter size and maternal ability) are only expressed by females.
A ram’s maternal EBVs, when halved, provide an indication as to how his female offspring will perform when they become mothers.

Litter size EBV
A ram with a litter size EBV of +0.3 is expected to produce ewe lambs that will have, on average, 0.15 more lambs than ewes from a ram with an EBV of 0.

Mature Weight
Positive figures identify breeding lines that will be bigger at maturity. In certain hill breeds, even though it is advantageous to enhance lamb growth rates, it may be desirable to restrict increases in the mature size of the ewe.
A ram with a litter size EBV of +0.3 is expected to produce ewe lambs that will have,
on average, 0.15 more lambs than ewes from a ram with an EBV of 0.

Carcase Lean Weight
This EBV estimates the genetic merit of the animal for muscle yield. It is assessed by measuring the quantity of muscle tissue (in kg) in the carcase using Computed Tomography (CT) image analysis of breeding stock at 21 weeks of age.

Carcase Fat Weight
This EBV estimates the genetic merit of the animal for leanness. It is assessed by measuring the quantity (in kg) of fat in the carcase using Computed Tomography (CT) image analysis of breeding stock at 21 weeks of age.

Muscularity/Gigot
This EBV estimates the genetic merit for carcase shape. The thickness of the muscle tissue in the gigot is assessed using Computed Tomography (CT) standardised to a fixed femur length and is measured in mm

Faecal Egg Count (FEC)
This EBV estimates the genetic merit of the animal for worm resistance. Faecal samples are taken from lambs at 21 weeks of age and submitted for laboratory analysis to measure the worm egg count in the sample

Breeding Indexes
EBVs are published for every measured trait which allows breeders that are making selection decisions to decide how much emphasis they wish to place on each trait. EBVs can also be combined into a multi-trait selection index, or breeding index, created to meet specific breeding objectives. It is widely agreed that this is the most efficient way to improve several traits at once. Economic weightings relevant to current market conditions can be used to ensure each trait is given the appropriate amount of emphasis in the index.