Growing replacement ewe lambs for mating
Many parts of the country are seeing a wet end to a warm summer, with others still struggling for grass due to the prolonged dry weather. Both extremes are resulting in tight availability of current grazing but potentially conserved winter forage too.
The focus for many will be getting the flock into the correct body condition score (BCS) for mating, but we must not forget to monitor growth rate of those selected as replacements to be mated as ewe lambs this autumn.
Ensure ewe lambs achieve 60% mature liveweight at mating
If your mature ewe weight is 70 kg, this means ewe lambs need to be a minimum of 42 kg at mating. This equates to a DLWG of 150‒200 g/day over the growing period. However, weigh a representative sample of your mature ewes to know what the liveweight on your farm is, this will determine what your minimum ewe lamb weight should be. Research from New Zealand (Griffiths et al., 2016) suggests that ewe lambs that are heavier at mating and ewe lambs that gained weight during pregnancy were more likely to rear a lamb(s) successfully.
Pre-tupping, aim for a pre-grazing sward height of 10‒12 cm and a post-graze height of 4‒5 cm when rotational grazing. As we move into autumn, allow sward heights to increase to allow for the increasing proportion of poor-quality forage at the base of the sward. A slightly higher sward height is needed to maintain intakes and body condition.
Regular weighing of replacement lambs will enable you to identify those that are on target and put steps in place if weight gain is not where it needs to be.
It’s likely that lamb growth rates could be affected by:
- Feed availability and quality
- Worm control in lambs to mating. Animals don’t acquire immunity to worms until they are over one year old
- Trace element deficiencies – check what your animals are deficient in by sampling their blood. Forage and soil analysis form part of the jigsaw but won’t necessarily reflect what is happening in the sheep. Remember, it might vary from year to year
To avoid a negative impact on future ewe production and longevity, ewe lambs need to continue to grow while they rear a lamb(s) to achieve 80% of their mature weight when mated as a shearling. They need 20% more feed during mating, early pregnancy and again during lactation. Avoid the temptation to overfeed during late pregnancy; this can lead to large lambs.
The AHDB funded Challenge Sheep project is currently entering its fourth year. Covering both sheep bred as ewe lambs and as shearlings, the project is tracking 7,000 replacements from a range of English sheep farms with the aim of developing best practice protocol for managing replacement ewes.
Griffiths KJ, Ridler AL, Heuer C, Corner-Thomas RA, Kenyon PR. The effect of liveweight and body condition score on the ability of ewe lambs to successfully rear their offspring. Small Ruminant Research 145, 130-135, 2016