SYNCHRONISATION OF OESTRUS IN DAIRY COWS USING PROGESTERONE ADMINISTERED BY "CONTROLLED INTERNAL DRUG RELEASE " (CIDR) DEVICES

The efficacy of CIDR devices (AHI, NZ) used either alone or combined with prostaglandins to synchronise oestrus was evaluated in a herd of lactating dairy c o ws l Onset of oestrus and fertility to artificial insemination (A.I.) at observed oestrus or to A.I. at a fixed time were measured, and the following treatments were compared: Group 1,.untreated cows that were inseminated at observed oestrus. Group 2, a CIDR was inserted for 12 days followed by A.I. at observed oestrus after CIDR removal. Group 3, a CIDR was inserted for 7 days with a luteolytic dose of prostaglandin F2a analogue administered on day 6. All animals were inseminated at 63h after CIDR removal followed by A.I. at observed oestrus. The proportions of cows showing oestrus during the first 5 days were 22%, 78 % and 87X, and by 25 days were 85%, 92 % and 98 % for groups 1, 2 and 3 respectively. In group 3, 83 % of animals had exhibited oestrus and 49% subsequently conceived to A.I. at the fixed time of 63h. Pregnancy rates after 25 days of mating as determined by rectal palpation were 46%, 62 % and 64 % for groups 1, 2 and 3 respectively. These results demonstrate that the CIDR is an effective device for synchronisation of oestrus in dairy cows, and when used in combination with luteolytic prostaglandins this synchronisation is sufficiently precise for successful A.I. at a fixed time. Key words: Dairy cattle, Reproduction, Oestrus synchronisation