MaximizingOR/CRFactorsL4L5

• Lambing percentage


  Number of lambs weaned divided by ewes presented for breeding
• What are some effects of poor LP?

  Less efficient ewes (less kg lamb/kg ewe), less lambs for sale/selection for replacements, poor utilization of spring feed - loss of pasture quality in summer
• Ovulation rate

  Sets potential for number of lambs weaned; key factor in lambing percentage
• Management plan


  Strategy to maximize ovulation rate within a ewe flock
• Liveweight


  Mean weight per 100 ewes; affects potential lambs born and failed
• Reproductive wastage 


  Survey data on potential lambs born, losses, and wastage per 100 ewes joined
• Static weight effect 


  Ewes that are heavier, have greater ovulation rates than lighter ewes
• Dynamic weight effect 


  High levels of nutrition in the weeks prior to breeding can increase ovulation rate (increases in weight)
• When is the response larger in the dynamic effect?

  Lighter poor condition animals
• A loss in LW during the dynamic effect will?

  Reduce ovulation rate
• Pt 2 - 57 to 57 kg = 78% multiple ovulations, is an example of which effect?

  Static effect
• Pt X - 63 to 57 kg = 65% multiple ovulations, is an example of which effect?

  Losing weight
• Pt 3 - 51 to 57 kg = 88% multiple ovulations, is an example of which effect?

  Dynamic effect
• What do farmers need to do to maximize ovulation rate but minimize the amount of feed consumed?

  Split ewes two to three months pre-breeding (i.e. at or around weaning), hold heavier/better condition ewes Improve the lighter poorer condition ewes by better feeding
• Pasture quality


  Key factors for ewes to gain weight: good quality, sward height, and pasture mass
• Pasture allowance 


  Minimum 4 kg DM/d for ewe to gain 100g/d
• Sward height


  Optimal between 4 and 8 cm for ewe intake
• Pasture mass


  Ranges from 1200 to 1800 kgDM/ha for ideal intake
• Poor quality indicator


  Pasture covers above 1800 kgDM/ha
• Intake restriction


  Ewe intake restricted below 1200 kgDM/ha
• Energy supplementation


  Increases ovulation rate, not common in NZ
• Protein supplementation


  Can increase ovulation rate, not widely used in NZ
• Crossbreeding advantage

  Allows faster increase in ovulation rate than within-breed selection
• Age of dam impact

  Ovulation rate peaks at 5-6 years, lowest in hoggets
• Breeding season timing


  Ovulation rate peaks at 3rd cycle, breeding can be timed to maximize ovulation rate
• Male effect


  Ram introduction to induce cyclic activity for early breeding
• When is the male effect only effective?

  Just prior to the spontaneous onset of breeding
• Phyto-oestrogens impact

  Red clover, lucerne can be used to increase ovulation rate if ewes graze these well before breeding/gain LW or condition, remove 3 weeks pre-breeding
• What does lucerne release in response to fungal infection and insect attack?

  Coumestan
• Mycotoxins impact

  Zearalenone reduces ovulation rates, active in autumn
• Facial eczema


  Caused by Sporidesmin from Pithomyces chartarium fungus found on dead ryegrass material
• What conditions does FE prefer?

  Moist and humid with warm nights in autum
• What affect can FE have?

  Loss in LW leading to lower ovulation rate
• How can sheep be protected from FE?

  Select resistant animals, zinc capsule, etc
• Ryegrass Endophyte Purpose

  Alkaloid in ryegrass protects it from insect attacks
• Ryegrass Alkaloid Effects

  Causes uncoordinated movement, heat stress, reduced intake/LW
• Ryegrass Staggers Impact on Ovulation Rate

  Results in live weight loss, reducing ovulation rates
• Parasite Stress on Ovulation Rate

  High internal parasite burden lowers ovulation rate due to live weight loss
• Exogenous Hormones for Ovulation Rate

  Androvax/multi-lamb immunization lifts LP by 14-20%
• Shearing just prior to breeding can result in a short period of non cycling and therefore drop in ovulation rate. Shearing should be avoided within 4 weeks of breeding.