Prostaglandins in oestrus management
Mechanism of action
Between day 6 and day 16 of the cycle (the period of natural prostaglandin F2α release) an injection of prostaglandin will induce regression of the corpus luteum ending the luteal phase. A new follicular phase begins and the animal will come into oestrus and ovulate. Fertility at the induced oestrus is similar to that of a natural oestrus.
Prostaglandins act on the corpus luteum, thus they can only be effective in cycling cattle.
Treatment schemes
Single administration
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Double administration
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Systematic administration, so called or targeted breeding
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Ovulation and insemination timing
Despite rapid luteolysis the interval to onset of oestrus after treatment with PGF2α is variable and dependent on the stage of the follicular development the animal is at when treated.
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Fertility rates for the systems based on prostaglandins
It is generally accepted that fertility, in terms of conception rates, of the cyclic heifer after prostaglandin treatment is not impaired compared with untreated control animals inseminated at a natural oestrus. However, conception rate in lactating dairy cows following prostaglandin treatment has been inconsistent and is sometimes lower than in control cows inseminated at a natural oestrus. The inconsistency in results between studies has been attributed to differences in management conditions, oestrous detection efficiency and accuracy.
As mentioned by Diskin et al., (2002) it has also been suggested that the lower fertility in prostaglandin treated cows may be due to the fact that a high proportion of cows are inseminated after having a short luteal phase. There is evidence for both heifers and cows that animals injected with prostaglandin at the late stage of the luteal phase have both a greater oestrous response and a higher conception rate than animals treated in the early and or mid-luteal stages (Nebel et al., 1998; Diskin et la., 2002).
Application in beef cows
Due to a high incidence of post partum anoestrus in beef cows, prostaglandins are not considered as the method of choice for oestrus management in this group of animals.
Should this method be nonetheless used it is an absolute requirement to ensure that the cows are cycling and in proper body condition.