Electing for growth rate without measuring the mature size of the ewe can increase the size of the breeding female over time. Where the aim is not to change the mature size, most breeders are interested in identifying “curve benders”, those animals that have high growth potential but do not increase the mature size of the breed. Where a breed, or flock’s, objective is to change the mature size then this can only be achieved by taking this weight and selecting animals using the Mature Size EBV.
Weighing gimmers before putting to the tup for the first time can monitor and identify genetic potential for Mature Size. Submit the weights to Signet on the Gimmer weigh sheets sent to you.
To ensure that the ranking of your animals is the best prediction we can provide, it is important that the data on which the EBVs are based is as accurate as possible. There are a number of opportunities for inaccuracy due to faulty equipment or human error, but we can all be a part of keeping the error rate as low as possible.
Signet ensures that there are validation checks at each stage of our data processing and Egenes also identify any extreme data and will exclude it from the analysis and issue error reports for Signet to act upon. All scanning technicians have to successfully complete accuracy and repeatability tests.
Not surprisingly, an incorrect animal’s weight within a “breed” analysis will have an insignificant impact on the analysis as a whole. At a flock level, particularly in small flocks, it can have a greater effect on the flock rankings and the individual’s EBV predictions.
Ensure that you record the details of the entire litter for any ewe’s lambing, not just the lambs you think are good or that you want to retain. Include all fostering and embryo transfer details.
Keep these in good condition and oil them before use. Check that they are weighing accurately by using a couple of 20kg bags of feed. It is important that the weights are accurate between 15 and 45 kgs at 8 weeks of age rather than worrying that the indicator needle always returns to zero.
Weigh lambs between the ages of 42 and 84 days of age to ensure that an adjusted 8 week weight is calculated. A weight at 8 weeks indicates that the ewe has reared a lamb and is used for the calculation of both 8 week and Maternal Ability EBVs. Usually a flock can find one day to weigh all lambs. If your lambing is protracted, or you lamb in two distinct periods, you may have to weigh later lambs on a later weigh day. Always work out the latest day to weigh by adding 84 days to the date the first lamb was born.
Whether you submit on a paper-based weigh sheet or send Signet the weights via email in a spreadsheet, please remember to indicate the weigh date/s and whether the weights are in lbs or kgs. It may seem obvious to you but a series of weights around 35-45 could be either lbs or kgs depending on breeding, feeding and management.
This is an important printout whether you use it for selection and culling purposes, or just for checking the data we hold on the database is accurate:
If you have submitted your lambing data in plenty of time, the technician will have received an electronic file of your flock. As each lamb is scanned the identity and sex is cross-checked and ensures another point of validation. When completed, the technician will leave a printout of the raw data showing all the lambs in your flock, sire and dam of lamb, and the scanning information including age at scan, weight, muscle and fat depths.
Check that there is a muscle and fat depth present for all lambs scanned.
If you have taken steps above to check your data, the final result printout should not need further checking for data accuracy and can confidently be used to aid selection decisions.
If you have not received an earlier printout, please follow the checklists above.
Using EBVs to make the best breeding decisions
Breeding evaluations are relatively risk averse, depending on good quality data to identify animals that are truly genetically superior. Don’t select sheep on EBVs alone, as this provides no guide to structural soundness, but equally don’t select them entirely “by eye”
Set flock breeding objectives – then identify EBVs of importance
Before making any breeding decisions consider your breeding objectives and the strengths and weakness within the flock
Select high EBV ewe lambs
Some flocks draft the ewe lambs they like the look of into a pen and then deselect those with poor EBVs; others select those with the highest EBVs and then cull those they don’t like. Both approaches should achieve the same objective
Cull low EBV stock ewes
In established flocks the regular replacement of older, low EBV stock ewes with high EBV shearlings will greatly increase rates of genetic gain. In new flocks the culling of stock ewes on their EBVs should be carried out with more caution, as less may be known about their true breeding potential, particularly for maternal traits
Consider using homebred ram lambs
These may be your best source of genetics. If usually sold as shearlings they may also provide a cost effective mating solution
Mate the top stock ewes with care
Only those ewes in the Top 20% of your flock are likely to produce a future stock ram worthy of use in the home flock. It is vital you get these ewes mated to the right sire. Occasionally a breeder puts all of their best ewes to a new unknown sire, this is a massive risk - which rarely pays off
Using well-known rams
Consider using at least one well-known (from a recording point of view) sire. The performance of their progeny will enable more accurate comparisons to be made to other recording flocks. This might involve exchanging or sharing recorded rams with other flocks
Test "unknown" rams as fairly as possible; ensure their progeny are born at the same time as those by other well recorded sires. Ensure they produce at least 10-15 fully weight recorded progeny in any year, more in large flocks
Use Accuracy Values
Accuracy Values indicate the likelihood that an EBV will change over time. They are useful when assessing the breeding potential of sheep from less well recorded flocks
All of these decisions should form part of an integrated breeding plan that also needs to minimise increases in rates of inbreeding