Friday, March 29, 2024

Merit in greater productivity

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Most of us would admit we could make better use of our ewes. After all, they’re an investment in our flock’s future productivity and profitability. About 20% of the genetic merit in a flock is because of ewes. The only time we have the chance to contribute to the average flock’s genetic merit is when we select young ewes as replacements. These ewes represent the most recent level of genetic potential.  Given that we generally don’t have individual performance data or SIL-derived estimated breeding values (EBVs) on these animals, the traits commonly selected for include size and-or weight, condition, wool type, structural soundness and so forth. All are poor indicators of genetic merit.
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More of us should be selecting flock replacements from ewes born as twins. This requires identifying twinning dams at pregnancy scanning, lambing them separately and marking the ewe lambs at tailing. Using this twin-born birth rank as a selection point will tend to lift the young ewe’s lifetime reproductive performance by about 3-5%.

When it comes to the older ewes to retain in a flock there’s not a lot to select for that’s positive. Of course we can continue identifying those ewes diagnosed as “twinners” at pregnancy scanning. That said many ewes cull themselves through death, being dry, age, poor weight-condition and so on. 

We should also acknowledge two things to ourselves. First, when it comes to selecting ewes to retain we do it with a mindset of culling – why else, when we call the job “ewe culling”? 

Second, when examining ewes for physical faults more selection scope is possible if minor variations that naturally occur in any flock are accepted.

What’s probably most important in making better use of ewes is making better use of sires. After all, the genetic merit of sires contributes about 80% of the average genetic merit to a flock so they represent a big investment in future ewe flock returns.

Buying rams with known genetic merit is a no-brainer. If the breeder isn’t using SIL EBVs in his own selections, or worse isn’t recording on SIL, what known genetic value are we getting for the outlay? 

We should be using breeders who select and sell on the basis of SIL EBVs. These records allow informed decisions to be made about the future genetic merit and profitability of a flock. Some breeders may provide actual data on a ram – for example birth rank, weaning weight, or a dam’s lambing history – but they’re all poor indicators of genetic merit.

At least half of lambs go to slaughter. It makes sense to split a ewe flock and integrate the use of specialist terminal and maternal sires. Using terminal sires – with appropriate SIL EBVs – can lift the potential income from the slaughter lamb operation through heavier weights and-or earlier slaughter.

The number of ewes put to a terminal sire depends on a flock’s lambing percentage. At a lambing of 130% we can afford to put about 45-50% of ewes to a terminal sire, which contributes about 60% of the total slaughter lamb kill. 

The remaining ewes go to a maternal sire and generate wether lambs for slaughter and potential flock replacements. We need to more effectively exploit the available specialised genetics in both the lamb slaughter profitability and maternal ewe productivity.

Another way to make better use of ewes is to allocate more ewes to a ram than the 80-100 commonly used. Putting ewes out at 120-150 to a ram means buying fewer rams each year, and with the same buying budget as before, allows purchasing of rams of higher genetic merit than at present. It’s unlikely that vulnerability to ram injury or failure will be increased. 

Assuming a mating mob of 1200 ewes, 10 rams would be required at 1:120. A 10% ram loss-failure would leave nine rams to 1200 ewes at 1:133 – a number the rams would handle comfortably.

Making more effective use of ewes increases the potential to improve future flock profitability. 

Most of that improvement will come from a more planned approach to the sire side of things – for example, which breeders are sourced from, the rams bought, the use of specialist maternal and terminal genetics, and how intensively those rams are used. It’s an investment I
reckon we can afford.

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