Ovulation Sheep

• Lambing percentage (LP)


  The number of lambs weaned divided by the number of ewes presented for breeding
• Effects of a poor LP

  • Less efficient ewes (less kg lamb/kg ewe)
  • Less lambs for sale
  • Less lambs for selection as replacements
  • Less selection pressure
  • Poor utilization of spring feed resulting in a loss of pasture quality in summer
  • Welfare indicator??
• The income from wool as a percentage of total farm income has dropped while the income derived from sheep (either sold store or direct for slaughter) has increased
• Increasing lambing % (but keeping weaning weight the same)

  Increases Cash operating Surplus per ha
• Lambing percentage of the mature ewe flock has increased over time
• The performance of our mixed aged lambing flock is on the rise
• Ovulation rate


  Ovulation rate of ewes sets the potential for the number of lambs weaned
• 60% of the variation in lambing percentage between farms is due to differences in ovulation rate
• After ovulation has occurred

  It is all about reducing losses to weaning
• Static effect of ewe live weight

  • The heavier the ewe the higher the ovulation rate
  • There is a plateau at BCS 3.0 or 3.5
  • a law of diminishing returns occurs
• If ewe weight increases in the six weeks pre-breeding

  Increases in multiples, but the increase decreases as the ewes get heavier
• Dynamic (flushing) effect


  • High levels of nutrition in the weeks prior to breeding can increase ovulation rate
  • Increases in liveweight
  • The response is larger in lighter poor-condition animals
  • A loss in live weight during this period will reduce ovulation rate
• How a ewe achieves her mating weight is often more important than the weight itself
• Managing the ewe flock to maximise ovulation rate but minimise the amount of feed consumed

  1. Split ewes two to three months pre-breeding and hold heavier/better condition ewes and improve the lighter poorer condition ewes by better feeding

  2. Six-weeks pre-breeding re-evaluate ewe live weight / condition and pasture availability

  3. Target flush those that would benefit the most from flushing

  4. Ewes need to be gaining at 100 - 150 g/d
• Flushing correctly requires a lot of feed
• What is required for a 60 kg ewe to gain 100g/d

  • Pasture allowance of at least 4 kg DM/d
  • Pasture of good quality (ME 11 or greater)
  • Sward height between 4 and 8 cm
  • Pasture masses of 1200 and 1800 kgDM/ha
  • Pasture covers above 1800 kgDM/ha can display poor quality
  • Pasture covers below 1200 kgDM/ha ewe intake is restricted
  • Intake of 1.6 to 1.8 kgDM/d
• Both energy and protein supplementation in diet can increase ovulation rate (not utilised in NZ)
• Plants with condensed tannins, which protect protein from rumen degradation, such as bird foot trefoil can result in higher ovulation, but this type of herbage hard to grow and maintain in NZ so not utilised to any extent
• Factors affecting ovulation rate


  • Breed
  • Age of dam
  • Time within season
  • Phyto-oestrogens
• Booroola gene


  • Single gene mutation that increases ovulation rate
  • One copy results in an increase in ovulation rate (OR) by 1.4/1.6
  • Two copies results in an increase in OR by almost 3.0
• Inverdale gene


  • This gene is found on the X chromosome
  • A ram can either carry one copy of the gene or no copies
  • A ewe can carry zero, one or two copies
  • One copies increases OR by 1
  • Ewes with 2 copies have small non-functional 'streak' ovaries
• Ovulation rate increases up until 5 – 6 years of age and is lowest in hoggets
• Ovulation rate increases up to the 3rd cycle of the season before starting to decline
• The 'male' effect can be used to advance the start of the breeding season and thus time of natural peak in ovulation rate
• Grazing ewes on swards with a high proportion of red- and sub-clover 3 weeks prior too and during the breeding period, will reduce ovulation rates and should be avoided
• Lucerne releases coumestan in response to fungal infection and insect damage which can reduce ovulation rate
• Red- and sub-clover


  • Formononetin is the oestrogenic compound
• Grazing ewes on swards with a high proportion of these plants 3 weeks prior too and during the breeding period


  Will reduce ovulation rates and should be avoided
• Newer varieties of these plants are less oestrogenic
• Can be used to increase OR if ewes graze these well before breeding and gain live weight/condition


  But then removed from these 3 weeks pre-breeding
• Formononetin


  Oestrogenic compound in red and sub-clover
• Pawera (red clover variety)

  • 0.34 ± 0.08% of herbage dry matter
• G27 (red clover variety – newer)


  • none
• Control (ryegrass white clover)

  • 1.09 ± 0.13% of herbage dry matter
• Lucerne releases coumestan in response to fungal infection and insect attack
• Coumestan is the oestrogenic compound
• Grazing lucerne with high coumestan levels 3 weeks prior too, and during the breeding period

  Will reduce ovulation rates
• Removing ewes off Lucerne 3 weeks pre-breeding will eliminate any potential issue
• Lucerne can be a good use to use it for ewes to gain weight well before breeding as a means of increasing ovulation rate
• Zearalenone (oestrogenic effects)