PRT-Texel Pure Performance
Interpreting Lambing Ease and Birth Weight EBVs for Texel Sheep
The recording of lambing ease scores is a routine part of the Texel Birth Notification process. EBVs are now available for this economically important trait.
Recording Lambing Ease
Lambing Ease EBVs take into account lambing ease scores and measures of birth weight. Lambing Ease scores are subjective assessment undertaken by the breeder using five categories that relate to lambing difficulty.
The scores are as follows:
1 = no assistance
2 = slight assistance by hand
3 = severe assistance
4 = non-surgical veterinary assistance
5 = veterinary assistance, surgery required
6 = elective caesarian
These scores relate to each lamb – so two lambs could have different scores. If you are unsure as to whether the lambing event has been assisted, then please leave the column blank.
The recording of this trait is optional, if you are not able to record it then please leave this column blank. If lambing difficulty score is blank, it is interpreted as no score recorded rather than “no difficulty”. Record a score for all lambs rather than just difficult or easy births. Scores should be recorded for dead lambs, if possible.
There needs to be some level of lambing difficulty in the flock for the scores to be used effectively in the analysis. Scoring all lambing events in a flock as 1 will not identify any genetic differences in ease of lambing (and not lead to high, positive lambing ease EBVs).
Interpreting a Lambing Ease EBV
The Lambing Ease EBV predicts the genetic variation that exists in a ram’s (or ewe’s) ability to produce lambs that are born without assistance. The EBV is expressed as the proportion of extra unassisted lambing events that are expected to arise from a particular sheep relative to one with an EBV of zero. High, more positive, Lambing Ease EBVs are more favourable.
The Lambing Ease EBV produced is a direct assessment of the ease with a ram or ewe’s progeny will be born. In the case of a ewe, it is not the measure of the ewe’s ability to give birth.
For example, a ram with an EBV of +6.0 would be expected, on average, to produce 3% more unassisted lambing events compared to a ram with an EBV of 0.0. The figure being halved, as rams will only contribute half of their genes to the next generation.
Estimated Breeding Values for Lambing Ease are calculated using lambing ease scores recorded at birth. The EBV will take into account data on all known relatives as well as performance data on related traits that are known to influence lambing ease – such as birth weight and muscling.
Recording Birth Weight
The birth weight of a lamb will influence how easily it is born and hence this measure is of interest in the analysis of lambing ease.
To record this measurement lambs should be weighed with 48 hours of birth. Weights should be measured, not estimated. There are a number of ways to collect this data; the easiest way for many breeders is to place lambs in a bucket hung from a spring balance.
Breeders should indicate in the column heading “Birth Wt. (kg/lb)”, by crossing through the irrelevant unit, whether the measurements have been taken in metric or imperial units. The recording of this trait is optional, if you are not able to record it then please leave this column blank.
Interpreting a Birth Weight EBV
The Birth Weight EBV predicts the genetic variation that exists in birth weight. The EBV is expressed in kilograms. Low, negative values indicate the genetic potential to produce smaller than average lambs; high more positive values indicate the genetic potential to produce larger lambs.
The use of this EBV must be made with care, as lamb survival is compromised most in both very small and very large lambs.
This EBV is a guide to help breeders avoid sires known to throw very large lambs, particularly where they are being mated to ewe lambs. Theoretically there may also be some high prolificacy flocks where an increase in birth weight may improve lamb survival.
A ram with an EBV of +2.0 would be expected, on average, to produce lambs 1kg heavier at birth than a ram with an EBV of 0.0. The figure being halved, as rams will only contribute half of their genes to the next generation.
As with Lambing Ease, EBVs for Birth Weight taken into account data on all known relatives as well as performance data on related traits.