Producing lambs that survive and thrive

In the excitement of measuring growth rate and improving carcase conformation, we occasionally forget our priority as terminal sire breeders is to ensure our rams produce live lambs that survive to the point of sale.

Many factors effect lamb survival, some are influenced by the environment the lamb is born into, some are influenced by the ewe’s maternal performance (whether she has enough milk and leads the lamb to shelter in wet weather). However, the lamb’s own genes also have a marked impact on their future and commercial farmers need lambs that are born easily, are fast to their feet and thrive.

As part of the genetic evaluation service provided by Signet to breeders, we can identify the best breeding lines for lamb survival; highlighting those sires whose lambs thrive and survive.

Producing breeding values for lamb survival

Lamb survival is a binary trait. A lamb either survives (i.e. it has a weight later in life) or it doesn’t, though in some cases the measurement may be set to “missing” where the trait hasn’t been accurately recorded; for example a flock with 100% lamb survival.

Records are analysed in flock-year groups, comparing the survivability of lambs born in a given flock and year. Survival records for lambs in flock-year groups where the percentage of dead lambs is abnormally low or high (<5% or >50%) are excluded from our analysis.

The heritability of lamb survival is lower than growth and carcase traits, which means less of the variation that we see in this trait is due to the animals’ genetics compared to these other performance traits. However, lamb survival has a high economic value and is well worth inclusion in our breeding programmes due to its impact on profitability – and also the carbon footprint of the national sheep flock.

The good news for terminal sire breeders is that we are entering a genomic age where information collected when genotyping animals will be used to enhance our analysis. Genomic breeding values for lamb survival will be even more informative in the future.

What should ram breeders do to enhance the recording of this trait?

• Those flocks that are performance recorded should capture as much data as possible to identify genetic differences in their flocks.
  • All dead lambs should be recorded.
  • All live lambs should be weighed.
• Collect DNA (genotypes) wherever possible.

More good news for breeders

Although our approach to evaluating lamb survival is relatively new, we generate breeding values using both historic and current information.  

For example trends for the Charollais breed show that this trait has improved over time, even without breeders having access to a breeding value.

Breeding lines with poor survival have clearly left the population as breeders start rearing lambs under increasingly commercial conditions. There may also have been some indirect benefits arising from an increase in birth weight when selecting for growth.

Messages for commercial producers

• Differences exist between sires and ram buyers can now select rams with superior genetics for lamb survival.
• Buyers should also take note of breeding values for traits like lambing ease and birth weight as both will indirectly influence lamb survival.
• Information on these traits can be found on the Signet website www.signetdata.com.