Is Collecting Weights At Marking Worth The Time And Effort?
We are seeing a trend in the industry as well as conversations related to people wanting to start recording marking weights and using them to inform selection decisions. Before you take this on read below.
Collecting marking weights and using them as part of a selection criteria is mostly a waste of time and effort, and absolutely a waste of time if there is no other data collected on the individual sheep to correct for the fixed effects at birth.
Marking weights are significantly affected by a number of fixed effects that have nothing to do with the genetic potential of the animal. These include:
- Date of birth (DOB) – therefore age at measurement
- Dam age
- Birth Type and Rear Type (BT and RT)
- Environment/feed (milk quality/quantity)
The most useful age based data to collect for your flock (or for your clients flocks if you are a stud) is at the time closest to the time of product marketing. For example, for prime lamb studs, measurements taken at the post weaning stage most closely relate to the expected marketing age of prime lambs and in commercial wool flocks, hogget and adult age stage wool measurements are the most important.
As there is no market for marking age lambs, collecting data at this stage has no relationship to a marketing opportunity and is highly influenced by the fixed effects at birth which increase the error in the data as a selection criteria.
It is our view that collecting weights at marking is simply making more work for yourself and adding cost.
Marking is a management event not a data collection event (unless you are adding sheep to your software and doing marking visual scoring). With weights, for example, a 6 week lambing date variation can produce 8-12kg of variation just because of DOB and that’s without including the other fixed effects at birth that affect weight.
The closer to birth, the more impact the fixed effects have on what you measure. Some fixed effects at birth alter the measurements for the life of the sheep (for example, the effect of birth and rear type in merinos on fibre diameter and CFW).
For a lot of measured traits, it isn’t really until the first adult stage that the fixed effects become less evident. This is why it is so important to capture data that affect as many of the fixed effects as possible for early stage measurements so that you aren’t disadvantaging sheep come selection time, It is also why ASBVs (and EBVs) are such a useful tool when they are based upon full data sets (it’s why mothering lambs at birth and recording actual DOB, BT, RT and full pedigree is the gold standard for data recording).
Whilst we don’t have a marking weight data set from a flock that also records the fixed affects at birth, the images below show weaning weights as an example. This data set is from a Border Leicester sheep stud that mothers up all sheep so it is very accurate in terms of the fixed effects. All weaning weights were taken on the same day for these sheep so it gives a proxy for marking weights but as previously mentioned, the influence of the fixed effects at birth would be even greater on marking weights.
You can see that the fixed effects at birth have a larger influence on the weaning weights that it is totally inaccurate to be selecting sheep based on weaning (or marking) weights without understanding and giving proper adjustment for these effects. This is what Sheep Genetics do when they calculate ASBVs which allow you to accurately compare animals.
We have attached a chart showing BWT ASBV vs Weaning Weight and WWT ASBV vs Weaning weight graphs. From these graphs you can see that there is very little relationship between BWT ASBV and weaning weights (and so marking weights) indicating that genetics play a small part in the weights at this age stage. You can see that the trend starts to consolidate when looking at the WWT ASBV vs Weaning Weight.
You may have wondered why there aren’t carcase ASBVs for the marking stage and this is the reason.
If you would like to play with the excel spreadsheet, you can here: