SIGNET RECORDING. Updated: 03/06/2008
Performance recording within the flock is carried out by SIGNET who run a scheme called Sheepbreeder and the Charollais Sire Reference Scheme (SRS).
In order to measure genetic performance an Estimated Breeding Value (EBV) is calculated for several traits and tied together to create an index for the animal. Traits measured that are of most interest in terminal sire breeds are for 8 week weight (a measure of the dam's mothering ability/milkiness), 21 week weight (the lamb's growth rate to 21 weeks of age), eye muscle depth and fat depth over the eye muscle. Other traits are also measured for ewe breeds. To calculate these EBV's, details of sire and dam are recorded, lambs are then weighed at 8 weeks of age and at 21 weeks. At the same time as the 21 week weighing, muscle and fat depth are measured using an ultrasound scanner and fed into a computer. This raw data is then sent to MLC headquarters in Milton Keynes and run through a complicated computer analysis called Best Linear Unbiased Prediction (BLUP), this takes the raw figures and removes the effects of management and environmental factors such as birth mode, rearing type, etc. This produces EBV's for each trait and an overall index as a measure of the individual's genetic merit, ie: that part of the animal's performance that will actually be inheritted, whereas liveweight will merely tell you which animal has been reared and fed best.
In flocks recording with Sheepbreeder, indexes in a flock cannot be compared from one year to another or from one flock to another. A high index lamb in a poor flock may be of lower genetic merit than a low index lamb from a genetically better flock, even though he may look bigger and better. How many people have purchased a big, strong show ram just to find that his lambs actually perform worse than their own? (I certainly have in the past!). As a result of this, few Sire Reference members will now purchase stock rams from outside the scheme and those that do will generally try him out on a small number of ewes in the first year.
Indexes in Sheepbreeder flocks are calculated so that the average performing lamb has an index of 100 each year, the best half of the flock having indexes over 100 and the worst half, below 100.
The next progression in producing more meaningful and accurate results is called Sire Referencing. Many sheep breeds now have a sire reference scheme (SRS) in place, the Charollais scheme was one of the first, beginning in 1990.
In an SRS, flocks are linked genetically each year so that indices can be calculated for lambs compared to all other lambs in all other flocks participating in the scheme. This linking is done by means of reference sires. Each year, scheme members are invited to take any ram lambs rated in the top 10% of the scheme on index that are suitable for use as stock sires to a selection day . Selection day for the Charollais scheme is usually in mid-June. There, a team of 4 rams (plus backups) are selected by members for use as reference rams the following year from which semen is then collected. Scheme members are then committed to use at least 20 semen doses, from two of the team of four available, over a cross section of their flock. In this way, genetically related lambs are born and reared in all participating flocks and performance of all lambs can then be compared as if in one 'super flock', the effects of differing management regimes having been removed. The average index in the first year was set at 100 and, because the genetics of all flocks are linked from year to year, indexes can be directly compared from one year to the next as well as from one flock to another within the scheme.
Genetic progress has been made rapidly by the scheme members with overall scheme index having increased by 163 points from1990 to 2003. Progress in flocks selecting replacement ewes and rams on scheme index has been markedly higher.
Superior lambs identified through ultrasound scanning are now scanned through a Computer Tomography (CT) Scanner in Edinburgh which shows lean meat, fat and bone quantities in the carcass with close to 100% accuracy. This gives an added accuracy to the lean index and highlights exceptional animals that may not have been highlighted by ultrasound measurements. An EBV for muscularity can now be calculated based on the thickness of the muscle at a given distance (100mm) down the bone in the hind leg. The two highest muscularity sheep found by 2003 are Rutland Alamos (ZFY 0025) and our own Lowerye Del Boy (ZVY 3198) who both have muscularity EBV's of around 8.30.
In 2004 the next progression in performance recording is taking place in the form of an across breed analysis. Connectedness through common genetics is such within the Charollais breed that a meaningful comparison can be made between all recording flocks in the breed rather than just within a sire reference scheme. Other changes to the index in 2004 include the incorporation of the muscularity EBV, calculated from the measurements made by CT described above. Another change is the application of the ATAN mathematical function to the fat depth EBV to penalise the index of excessively lean sheep, those that breed lambs that are perceived to be slow to finish on a traditional, forage based, diet.
Index is however not the whole story. As stated earlier, an animal's index is made up of individual trait EBV's. In order to select a ram best suited to a management system we need to decide which of those traits are most important. For instance, a very low fat EBV will give a high overall index but the progeny are unlikely to finish on a low input, forage based system such as the typical British spring-lambing flock. They would however perform very well on an intensive early-lambing system with high input levels, resulting in higher carcass weights at a given fat class. This problem has been addressed to a great extent by the application of the ATAN function mentioned earlier. A common complaint from farmers buying a high index ram is that the "lambs wont finish without feeding", the answer is almost always that they have used the wrong type of ram for their production system. In the Lowerye commercial flock, we use ram lambs from the top 5% of the sire reference scheme selected for high growth rate and muscle depth (obviously important traits on any system) but not excessively low levels of fat. As a result, we finish March born lambs from medium sized Texel-x ewes at 40-48 kgs (depending on market requirements) and off a forage diet only.
Recent farm scale trials have indicated that the faster growing and leaner carcasses produced from using high index rams is worth at least an extra £2 per crossbred lamb to the commercial producer. Depending on the lambing period, this is worth between £600 and £1,000 additional income over a ram's lifetime. Several farms have demonstrated an additional income of £6 to £12 per ewe mated. This benefit can be even more if a ram is used more widely, through AI. We sold a shearling ram with scheme index of 265 at the 1998 Premier Sale to a consortium of farmers wishing to try a high index ram through AI, primarily on early lambing ewes. That ram was used on several hundred ewes in the first year through cervical AI. These farmers reported a significant increase in sale weights at a similar fat class and the lambs reached these weights on average two weeks earlier than lambs sired by their old rams. They are all now convinced as to the benefits of purchasing rams on the basis of their Sire Reference performance figures.
We have many other commercial farmers who purchase rams privately on the farm on the basis of scheme indices, all of whom have been totally convinced through experience. The number of these enlightened customers is growing annually.
Our average eye muscle depth, measured by ultrasound scanning, has increased by a huge 33% in the decade since we started recording and selecting on those records. In the real world, that equates to a chop with a third more meat in it!