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Stocking rate and the number of lambs weaned per ewe are two key factors influencing the gross margin attainable in sheep enterprises. High-prolificacy genetics has the potential to considerably enhance the number of lambs produced.
However, as we saw this year, there is significant potential through the adoption of improved management techniques and adequate nutrition pre-breeding to also lift the number of lambs produced from the existing ewe breed on many farms.
Favourable conditions
A high percentage of mid-season lambing flocks experienced more favourable breeding performance in recent years despite not making any significant changes to their system. The higher breeding performance was demonstrated through an increase in litter size, lower barren rates and tighter lambing spreads.
While management practices differ, a common factor across farms in the second half of the year was improved grass supplies. The positive grass supplies led to an improvement in ewe body condition, which has been proven to increase ewe litter size.
Condition score and litter size
The advantages of having ewes in the correct body condition are significant. Teagasc research, carried out by Tim Keady and Noel McNamara in Athenry, shows that each body condition score (BCS) unit increase at mating (within the range of BCS 2.5 to 4) has the potential to increase litter size by 0.13 lambs per ewe put to the ram.
Results coming from the Teagasc BETTER farm sheep programme add backing to this statement.
Research also shows that the greatest benefit in increasing litter size is achieved from ewes brought from a lower base, with the advantages diminishing as they approach or exceed target condition.
As such, there is a huge benefit to be gained in identifying ewes that require preferential treatment. There are additional advantages outside of an increased litter size, with ewes in optimum condition cycling earlier and achieving tighter lambing spreads.
Target condition
Body condition scoring of ewes is the most accurate method of assessing ewe condition. It is easy to carry out and while the accuracy can vary slightly between operators, it is a good technique to monitor changes in ewe condition and suitably for breeding.
The target condition score for lowland ewes at mating is 3.5 to 4.0. Increasing one condition score generally equates to an increase of 9kg to 12kg liveweight in most lowland breeds with a mature weight of 70kg plus.
Mature ewes grazing good-quality grass will gain in the region of 0.8kg to 1kg liveweight per week. This means that for ewes to improve from a condition score of 2.5 to 3.5 requires about nine to 10 weeks feeding on good grass. The rate of increase may be faster where ewes are grazing reseeds or after-grass swards.
Increasing condition
The fact that it takes nine to 10 weeks for ewes on good-quality grass to gain one condition score underlines the importance of putting plans in place well in advance of the start of the breeding season.
Post-weaning ewes should be tightened up on bare pasture for a period of about 10 days to dry off sufficiently and reduce the risk of mastitis. Ewes can be assessed on condition at weaning, or once they are weaned satisfactorily, with animals that need to be culled identified first.
Ewes should be split into groups with parameters set on body condition. Where there is a significant variation, ewes should ideally be split into three groups – one group in very poor body condition of less than 2.5 and requiring close attention; another group at BCS 2.5 to 3.5 and requiring access to good-quality grass; and a final group in BCS 3.5+ requiring maintenance or slightly below maintenance feeding.
It is difficult on most farms to be in a position to divide ewes into three groups and also graze lambs. An approach taken on some farms is to graze in a leader-follower system, with ewes in very poor condition grouped with finishing lambs (ewe or wether lambs).
This group can be followed by ewes in average body condition, with the final group used to graze out pastures to 3.5cm to 4cm and promote high-quality grass regrowth.
On many farms, there are likely to be paddocks that have developed a thick butt of stemmy material in recent weeks. Dry ewes requiring maintenance feeding are ideal to graze these areas.
Ewes grazing for maintenance will require in the region of 0.8kg to 0.9kg grass dry matter (DM) intake per day, while ewes grazing good-quality grass will consume 1.3kg to 1.4kg DM per day. It should be noted that it is important to monitor ewes regularly and switch ewes between groups to avoid ewes gaining or losing excessive condition.
Preference to ewes
The mistake is often made of giving sole preference to lambs and cull ewes post-weaning with breeding ewes stocked heavily and little monitoring of condition until close to the breeding season. It is vital that steps are taken to avoid this.
Grass supplies are presently good, meaning that there should be scope to ensure ewes receive the attention they require. Where grass supplies are tight, a strong trade for store lambs and cull ewes provides the option of trading a percentage of animals and reduce grass demand.
It is also important to manage grass supplies to ensure high-quality grass will be available in the run-up to and during breeding.
Providing ewes with adequate condition up to breeding and failing to maintain a high level of nutrition in early pregnancy can result in poor attachment of the embryo to the wall of the uterus and embryonic loss.
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