Driving reproductive performance by removing the 'passengers'

Author: Amy Lockwood, AWI Extension WA

Lifetime reproductive performance is a key driver of the profitability of Merino enterprises. Reproductive efficiency, selection pressure and consistency of production within a flock can be increased by identifying breeding ewes with poor performance to remove from the replacement breeding flock, i.e. the ‘passengers’ or bottom 25% of ewes. It’s also important to identify those with superior performance to retain in the breeding flock, i.e. the ‘performers’ or top 25% of ewes.

Assessing udders as ‘wet’ or ‘dry’ at lamb marking is one of several tools used to identify passengers and performers. A ‘wet’ udder assessment 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.

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. 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.

Udder assessment is best done at lamb marking and is recommended for both flocks that do and do not pregnancy scan. Udders can be assessed at weaning but you may incorrectly assess ewes as ‘dry’ if they have naturally weaned their lambs before you conduct weaning (for example, ewes that conceived early in the joining period and have 14-week-old lambs at foot). Assessing udders at lamb marking is the most reliable way of identifying ewes that have conceived and reared lambs if you do not pregnancy scan your ewes.

What to look for

Dry ewes that were not pregnant or have failed to lamb will have the smallest udders, no stain on the breech, and they are often fatter. Maiden ewes that are dry will have no udder development, whereas older ewes that have previously lambed (in a previous year) will have some udder development.

Keep an eye out for udder abnormalities

Damaged or abnormal udders reduce milk supply to the lamb/s, 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.

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
• Abnormal udder development
• Cheesy gland

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.

Wet-or-dry assessment is a quick, cheap, and simple practice that can be undertaken when the 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.

More information:

• AWI Picking Performer Ewes™ workshop
• NSW DPI factsheet on udder assessment