25 July 1997

EBv figureS Make for easier choice

Estimated breeding values will help producers select genetically superior rams and improve flock performance. Signet consultant Maurice Jones explains how they work

WHEN selecting for more productive sheep most breeders -whether pedigree or commercial – would agree that the performance of any animal is determined by several factors.

These include the animals own genes – inherited from its parents – and how it has been fed and managed. But only the genes are passed on to future generations.

All UK sheep producers are currently striving to produce a top quality product at sensible cost for todays demanding market. But what has that got to do with estimated breeding values I hear you say.

Pedigree breeders involved in the Signet Sheepbreeder recording service are striving to find those sheep in their flock or breed which are better than their predecessors, and will leave permanent gains in the next generations.

The improvements may be small on a yearly basis, but build up into quite large commercial gains over a period of years. These gains certainly benefit the individual breeder, but in the main are passed to the commercial sector where they mean extra profit when sought out and used correctly.

It does mean one thing though, the commercial producer must go out and actively seek those sheep which will improve individual flock performance and profits.

Breeders who are recording go through quite a process of paperwork to arrive at the ultimate answer. Breeding records are kept for individual sheep and lambs are weighed at eight weeks and evaluated for maternal traits. They are weighed again at 20-21 weeks, backscanned for eye muscle depth and backfat depth, and evaluated again for maternal and carcass characteristics.

Breeding indices and estimates are then produced as to how good – or bad – they are for each particular aspect compared with their contemporaries.

The computer technique used to produce these indices is called Best Linear Unbiased Prediction (BLUP).

All we really need to understand is that it is a complex computer programme that is able to take into account all the information it can find relating to an animal, make allowance for rearing type, management regimes and all other variables affecting the particular animal and calculate the most accurate estimate of an animals potential.

This type of analysis is common language in dairy, beef and pig breeding industries, and is rapidly gaining recognition in the sheep world.

These measurements, together with all the other information on file, are combined into a lean index or scheme index depending on whether the breeder is running a within flock evaluation, or is a member of a sire reference scheme.

The higher the index the better the overall performance. But buyers must be aware that within flock evaluations have an average lean index of 100, while sire reference groups will have their own scheme index displayed on performance cards – typically around 150-155 points.

That language is presented to the industry using a variety of EBV titles, and displayed at sales or on records in an easily understood format:-

So what are we saying about this sheep?

At eight weeks it is superior to its contemporaries by 2.9kg, while at scanning its weight advantage compared with the average has improved to 5.1kg. It is better on muscle depth by 3.5mm and has 0.5mm less fat, and so its a good ram in all departments.

Assuming an individual will pass on half its genes to its offspring we can see the benefits which will accrue. Taking the scan weight as an example, we can expect a benefit of around 2.5kg in the progeny.

If we assume the ram has had 40 ewes mated to him, which have produced 70 lambs, then they have the potential to be 2.5kg heavier at the same age, or a total of 175kg greater liveweight.

In practice, this will reflect in either more lamb weight being sold as they are leaner and can be taken to slightly higher weights, or they can be sold one or two weeks earlier – particularly important in early lambing flocks with high creep feed costs.

Early lamb producers should be looking for rams with good growth EBVs and negative EBVs for fat depth. This will lessen the time lambs are on farm, and allow more flexibility in marketing as lambs will not become overfat so quickly.

Using high growth sires can save a week on sale time. This means less creep used at a time when lambs are eating and costing most. Seven days saved, at say 2kg of feed/lamb/day at £200/t, can mean a saving on feed costs alone of £2.80/lamb. Thats £280 for every 100 lambs – a considerable saving.

Store lamb producers should be searching out rams with good growth and muscle EBVs to give them a well grown, good fleshed lamb to sell on for finishing. Well grown and fleshed lambs can command £3-£4/head premium, leaving more profit – and a better lamb for the finisher, who comes back next year.

The addition of new maternal traits – prolificacy, maternal ability and mature size – will allow producers to switch or add to their breeding selections in individual flocks or breeding groups.

Unlike the other traits, these are expressed as an index ranging from -1 to +1, giving an accurate indication of the genetic trend, rather than, for instance, exact figures for number of lambs born in the case of prolificacy.

These new figures give producers the option to select for specific maternal traits. For instance, where an increase in litter size is required, producers could select females with the highest index figures as replacements. But where prolificacy is sufficient, say in Cambridge flocks, producers could select the females with average litter size, or those scoring zero. Selecting females with a negative score would obviously reduce litter size.

The selection of a female with positive EBV for prolificacy may not be seen as significant, but over a period of years that positive ewe may be related to, and responsible for, 20-25% of the breeding females in a flock. As ewe premium payments and lamb prices decline, numbers reared will increasingly affect farm profits.

Prolificacy

Breeders concerned with prolificacy can opt to select for more lambs born while keeping an eye on muscle and fat levels. This is particularly useful for prolific lowland ewes and hill ewe breeds producing cross-bred females for lowland producers.

Producers aiming to improve carcass quality, but worried about losing out on prolificacy or milk yield (the eight week weight) will be able to easily monitor maternal performance as well as selecting for leaner, better fleshed sheep.

And the selection of rams with positive maternal EBVs is even more important. They can have a large influence, over perhaps half of the breeding females available for selection and future breeding in any year.

Hill sheep producers can also benefit from maternal EBVs where they aim to increase mature size of their sheep. Shearlings can be weighed prior to their first tupping and that information included in the breeding programme. Maternal traits in these flocks are important, and the indices, combined with scanning to help ram selection, will improve the conformation of cross-bred ewes supplied to lowland producers.

Independent trials carried out by SAC in Scotland, and MLC/Charollais Society trials in Wales, have conclusively shown that using high index rams can be worth at least an extra £2/lamb to the commercial producer. Depend-ing on the lambing and rearing season this is worth between £600 and £1000 additional income over a rams lifetime.n

Using rams with good growth and muscle EBVs will give well grown, good fleshed lambs, which will command a premium in any market.

BLUP BENEFITS

&#8226 Increased profits.

&#8226 Select for specific traits.

&#8226 Improved productivity.

&#8226 Track flock improvement.

The new maternal traits – prolificacy, maternal ability and mature size – will allow producers to switch or add to their breeding selection criteria.


Ear no 97010

EBVs

Eight week weight (kg)+2.9

Scan weight (kg)+5.1

Muscle depth (mm)+3.5

Fat depth (mm)-0.50

Lean index or scheme index187

Flock average100 or 155