L4

• Calving performance


  The reproductive performance of a beef cow herd

  
• Compact calving


  A calving season where the majority of cows calve within a short period of time

  
• Calving pattern


  • The number of cows calving in each 21-day period
• Calving date


  The ideal time for calving is mid to late September, some in October
• Target reproduction goals


  • 12 month (365 day) mean calving interval
  • 63 day (3 cycles) mating period for cows (49 days sometimes)
  • 95% or more of the cows joined with bulls in calf at the end of breeding
  • Mating of heifers for only 42-45 days (2 cycles) with an 85% in-calf rate
  • Up to 70% of cows and heifers calve during the first 21-day mating period

  
• Pregnancy rate (PR)


  % cows mated that are pregnant/scanned in calf

  
• Calving percentage (CP)


  % cows diagnosed pregnant that wean a calf

  
• Reproductive efficiency = PR x CP = 90%
• Likely reproductive problems


  • Poor pregnancy rate as assessed at pregnancy testing
  • Poor weaning percentages
  • Poor weaning weights
  • Abortion investigation
• Calving pattern - poor hill country

  • Calving 1 August - 15 November
  • Breeding 1 November - mid February
• Calving pattern - preferred

  • Calving 25 August - 28 October
  • Breeding 1 December - 1 February
• Condensed calving pattern


  Increases average weaning weight by 28kg compared to typical pattern
• Calculated Conception Rate (CCR)

  Measure of reproductive rate for a specific length of the mating period
• Factors affecting CCR


  • Fertility of the bulls
  • Fertility of the cows
  • Venereal diseases in the herd
  • Nutrition (esp. energy balance & grass cover)
  • Topography
  • Heifers at target weights
  • Bull : Cow ratio

  
• How to correct a spread-out calving

  1. Record number of calves born weekly

  2. Pregnancy test and foetal age

  3. Decrease herd size by culling late calvers

  4. Replace culls with early calving heifers

  5. Mate heifers for only 42 days

  6. Delay mating to ensure cows are cycling

  7. PD at correct time 6-7 weeks after end mating to assist in foetal aging

  
• Artificial breeding


  Use to obtain access to bulls which would otherwise not be available and improve rates of genetic improvement
• Artificial breeding is limited in commercial beef herds due to intensive labour input required

  
• Fixed time AI with oestrous synchronisation

  1. Control the oestrous cycle so animals can be bred at a pre-determined time

  2. May use as means of getting more pregnant early in breeding season

  3. For more efficient use of labour at calving

  4. To allocate feed more accurately over pregnancy

  5. Produces a more uniform calf crop
• Treatment for fixed time AI

  1. Day 0: Intravaginal progesterone device and GnRH

  2. Day 7: Removal of progesterone device and injection of PG

  3. Day 9 (AM): GnRH and fixed time AI
• 7 day synchronisation for cows, fixed time AI for maiden heifers