Ewe genotype – the key factor influencing ewe productivity

Tim Keady Teagasc Research Officer examines how ewe genotype affects ewe productivity and lamb performance.

Main Messages

• Ewe genotype has a big impact on ewe productivity i.e. number of lambs reared per ewe joined.
• High levels of performance are achievable for grazed grass
• Use of prolific ewe genotypes can produce 6 additional lambs during their productive lifetime
• The additional lamb carcass due to increased ewe productivity is equivalent to €35 annually or €160 per ewe during her productive lifetime

Introduction

It is estimated that the ewe replacement rate for the national lowland flock is approximately 22%. Replacement ewes normally join breeding flocks at 18 months of age with the intention of producing their first litter at 24 months. Replacements are a major cost in mid-season prime lamb production systems. The cost of replacement ewes at joining at approximately 18 months of age is equivalent to 25% of the value of lamb carcass output that they will produce during their lifetime. One way of reducing replacement cost is to increase litter size and thus the number of lambs weaned per ewe joined. The results presented in this paper are for ewes aged 2 to 6 years.

Athenry study

An on-going study at Athenry was designed to evaluate the effects of ewe genotype [≥75% Suffolk, Suffolk×Belclare, purebred Belclare] on ewe lifetime performance. The Suffolk was used because 55% of the national lowland flock comprise of Suffolk types. Belclare were chosen because of their proven high productivity. All ewe were joined with Charollais rams.

All lambs reared as singles and twins were turned out to pasture within days of birth and received no concentrate supplementation prior to slaughter. Lambs reared as triplets were offered up to 300g concentrate daily until weaning and then no concentrate was offered prior to drafting for slaughter. Lambs were drafted monthly at predetermined live weights with the objective of achieving carcass weight of 21 kg. All lambs were drafted for slaughter prior to the end of the grazing season.

Effect of ewe genotype on performance

The effect of genotype on ewe productivity is presented in Table 1. Belclare and Suffolk×Belclare ewe produced larger litters than ≥75%Suffolk ewes.  Relative to the ≥75% Suffolk ewes, Belclare and Suffolk×Belclare ewes reared an additional 0.28 and 0.35 lambs per ewe joined, annually.

The effect of ewe genotype on lamb performance is presented in Table 2. Lambs born to Suffolk×Belclare ewes were heavier at weaning. Lambs born to Suffolk×Belclare were drafted for slaughter 6 and 10 days younger than lambs from Belclare and ≥75% Suffolk ewes, respectively. Lambs from Belclare and Suffolk×Belclare ewes were a similar age at drafting for slaughter. Assuming the national replacement rate of 22% Belclare and Suffolk×Belclare ewes produced 1.3 and 1.6 extra lambs during their lifetime relative to ≥75%Suffolk ewes. This increase in ewe productivity, due to changing ewe genotype, is equivalent to €35 per ewe annually or €160 per ewe during her productive lifetime.