Oestrus synchronisation with a prostaglandin analogue: I. Systems in lactating dairy cattle

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Abstract
Three trials were completed to compare different regimes for the use of an analogue of prostaglandin F2 alpha(“Estrumate”: ICI) in the breeding management of herds of lactating dairy cows with seasonally concentrated calving patterns. The first regime involved two injections of ‘Estrumate’ 11 days apart, followed by insemination, either at 72h and 96h after the second injection, or at the first observed oestrus. Every cow had calved at least 40 days before the first injection. The second regime involved a single ‘Estrumate’ injection given to every cow not inseminated during the first seven days of the breeding programme. Treated cows were inseminated when observed in oestrus within 48h of injection, or at 72h and again at 96h. The third regime utilised the technique of tail-painting during the pre-mating period to identify groups of cycling cows which were subsequently givena single injection of “Estrumate” and inseminated 72h lateror at a subsequent behavioural oestrus. All regimes significantly altered the conception pattern from that obtained in untreated herd-mates. The variable incidence of post-partum anoestrus, genuine short oestrous cycles and the degree of precision in oestrus synchronisation in lactating dairy cows resulted in many animals being unnecessarily injected and/or inseminated. The third regime overcame most of these problems and could have application in many largeherds. The identification of cycling animals and insemination at detected oestrus are important components of programmes using prostaglandins for the purpose of oestrus synchronisation in lactating cows in seasonal dairy herds.