Who are the real performers driving your flock’s reproductive results?
Lifetime reproductive performance is a key driver of the profitability of Merino enterprises. Reproductive efficiency, replacement ewe selection pressure and consistency of production within a flock can be increased by identifying breeding ewes that are consistently bringing results to the yards at lamb marking. These gains can be substantial if you have not previously used reproduction performance as a criteria for selecting your ewes.
Author: Megan Rogers, AWI Extension NSW Project Manager
The key is in the name – the job description of the breeding ewe is to breed lambs, to generate the self-replacing progeny that align with your breeding objective and drive your flock forward. Of course, there are other key parameters in your breeding objective upon which selection decisions are made, but if she is failing to produce lambs then she is simply a glorified wether.
How can you hold your ewes accountable?
In a commercial operation, holding breeding ewes (and your management) accountable at lamb marking is where the process is most accurately conducted. Assessing udders as ‘wet’ or ‘dry’ at lamb marking is one of several tools used to identify passengers and performers. A ‘wet’ udder means that the ewe has reared at least one lamb. ‘Dry’ ewes are those that have lambed and failed to rear a lamb, also known as ‘lambed and lost’.
If you don’t pregnancy scan, dry ewes could also be ewes that failed to conceive. Udder assessment at lamb marking time is a must-do task irrespective of whether you pregnancy scan or not (though pregnancy scanning comes highly recommended). It is the most reliable way of identifying ewes that have conceived and reared lambs if you do not pregnancy scan your ewes.
If you do pregnancy scan, performing wet-or-dry assessment at lamb marking is still highly recommended to identify ewes that have failed to rear a lamb.
Leaving this important task until weaning runs the risk of mis-identifying ewes that conceived early in the joining period and lambed early. These ewes will often have naturally begun to wean their lambs and dry off, thereby penalising a high-performing ewe.
Passenger vs. performer ewes
Ewes are considered performers if they are assessed as wet each year, successfully rearing a lamb at their first two lambing opportunities. In contrast, passengers fail to rear a lamb at their first two lambing opportunities.
Passenger ewes:
- represent 70% of the dry ewes in the flock.
- contribute 45% of the total lamb mortality in the flock.
- fail to produce a lamb for their first two attempts.
- learn and repeat poor maternal behaviours.
Performer ewes:
- rear at least one lamb each year, succeeding at their first two attempts.
- produce 3.4 more lambs for their first four attempts.
- represent 5% of dry ewes in the flock.
- rear 90% of their lambs (which are mostly twins).
To put this into a lifetime value perspective, let’s look at some numbers.
| PASSENGERS – BOTTOM 25% | PERFORMERS – TOP 25% | |
|---|---|---|
| Reproductive performance | Rears 1.2 lambs from 4 attempts | Rears 5.6 lambs from 4 attempts |
| Wool production and quality | Cuts +0.15 kg CFW* – lower SS# | Cuts -0.15 kg CFW* – higher SS# |
| DSE^ rating | 1.37 DSE^/year – looks fatter | 1.57 DSE^ – looks leaner |
| Lifetime economic value | $585 | $1,198 |
| $/DSE^ | $78/DSE^ | $137/DSE^ |
Source: AWI Picking Performer Ewes
CFW* = clean fleece weight
SS# = staple strength
DSE^ = dry sheep equivalent
Research has shown that culling passenger ewes that have consecutively failed to rear a lamb (twice lambed and lost) has a similar impact on lifting the reproductive performance of the flock as culling ewes that consecutively fail to conceive (i.e. ‘twice-dry ewes'). The main benefit of culling these ewes is a decrease in the number of dry ewes in the flock, leading to increased reproductive rates.
It is also important to note that maternal behaviour is not highly heritable (though there is good variation in sheep performance for the trait, meaning there is opportunity to pick better performers and make progress) but it is repeatable. This means that identifying the passengers at every pregnancy scanning and lamb marking will provide cumulative improvements in net reproductive rate (NRR).
What to look for at udder assessment
| Wet ewes | Dry ewes |
|---|---|
| Full, warm udder (N.B. some ewes may only be lactating on one side of the udder) | Small, floppy/soft, cool udder with some development |
| White, opaque milk stripped from teat | Fluid may be difficult to strip from the teats. The fluid is different to milk and may range from watery to thick, be clear or various colours different to the colour of milk, and may have white flecks. |
| Clean teats | Dirty/greasy teats |
| Birth stain on breech | Birth stain on breech |
Keep an eye out for udder abnormalities
Damaged or abnormal udders reduce milk supply to lambs, significantly compromising lamb performance and survival.
Take the opportunity to identify any udder abnormalities when assessing ewes as wet or dry. Ewes with mastitis or unsound udders should be culled. These ewes contribute to future lamb losses through their faulty udder.
Udder abnormalities include:
- Mastitis
- One or both sides of the udder are hard and often lumpy.
- Milk stripped from the teat may be watery and have clots, blood or pus.
- If the ewe has ‘black mastitis’, the udder will look black/purple and feel colder than normal due to the death of the tissue. These ewes will require treatment with antibiotics.
- Missing teats
- Teats damaged from shearing cuts
- ‘Blown’ or ‘bottle’ teats that are much too large and prevent the lamb from drinking
- Blind teats (no opening in the end of the teat for milk release)
- Abnormal udder development
- Cheesy gland.
Want to make 75% more gain in your flock?
Several factors influence the reproductive performance of ewes and it is important to utilise all available tools to lift the reproductive performance of your flock and profitability of your business.
More than three quarters of the potential gain in net reproductive rate (NRR) in a self-replacing Merino flock is due to within-flock selection.
Wet-or-dry assessment is a quick, cheap and simple practice that can be undertaken when ewes are already yarded for lamb marking.
If wet-or-dry assessment is not a routine practice in your enterprise, give it a go at lamb marking this year and reap the rewards.
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