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Development of a gonadotrophin-releasing hormone and prostaglandin regimen for the planned breeding of dairy cows
  1. A. R. Peters, BA, DVetMed,PhD, FRCVS, FIBiol1,1,
  2. I. Mawhinney, BVSc,MRCVS2,
  3. S. B. Drew, BSc, PhD3,
  4. S. J. Ward, BSc, PhD1,
  5. M. J. Warren, BSc1 and
  6. P. J. Gordon, MA, VetMB,CertCHP, MRCVS1,2
  1. 1 Department of Farm Animal and Equine Medicine and Surgery, Royal Veterinary College, Boltons Park, 44 Hawkshead Road, Potters Bar, Hertfordshire EN6 1NB
  2. 2 Intervet UK Ltd, Science Park, Milton Road, Cambridge CB4 4FP
  3. 3 ADAS Bridgets, Bridgets Lane, Martyr Worthy, Winchester, Hampshire S021 lAP

Abstract

Four studies were carried out to determine the ovarian responses of dairy cows undergoing natural oestrous cycles to sequential injections of gonadotrophin-releasing hormone (GnRH), followed seven days later by prostaglandin and, 48 to 72 hours later, by a second injection of GnRH. In study 1, of 60 cows so treated, 47 were in the intended periovulatory phase when a fixed-time insemination was given 72 hours after the prostaglandin. In study 2, detailed observations were made in 32 cows treated as in study 1, using ultrasound to determine the optimum time to administer the second dose of GnRH. Ovulation was most effectively synchronised by giving GnRH 56 to 60 hours after the prostaglandin. Study 3 investigated the timing of ovulation when no initial dose of GnRH was given. Six cows were injected with prostaglandin on day 12 of the oestrous cycle, followed by GnRH 60 hours later. Five of the six cows ovulated 24 to 36 hours after GnRH, an equivalent timing and synchrony to that in study 2, in which a dose of GnRH had been given seven days before prostaglandin. In study 4, an initial dose of GnRH was given to six cows late (day 17) in the oestrous cycle, and prostaglandin seven days later. The GnRH treatment delayed luteolysis in five of the cows so that they were responsive to the prostaglandin and ovulated 24 to 36 hours after the second dose of GnRH. The use of GnRH (day 0) - prostaglandin (day 7) - GnRH (day 9.5) appears to be an effective means of synchronising ovulation in most cows.

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      Footnotes

      • Professor Peter's present address is Pfizer Central Research, Sandwich, Kent CT13 9NJ

      • Mr Gordon's present address is Hampden Veterinary Hospital, Aylesbury, Buckinghamshire HP20 lRP

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