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The use of an enzyme immunoassay for milk progesterone for evaluating dairy herd facilities

Hariadi, Mas'ud (1987) The use of an enzyme immunoassay for milk progesterone for evaluating dairy herd facilities. Masters by Research thesis, Murdoch University.

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The overall objectives of this study were to evaluate the use of a milk progesterone enzyme immunoassay to investigate reproductive activity in post-partum dairy cows and to evaluate fertility in the dairy herds. An enzyme immunoassay for progesterone in milk was established which conformed to requirements in terms of specificity, precision and sensitivity (4 pg/10μ ). The concentration of progesterone in plasma and milk had a high correlation (r=0.96). The concentrations of progesterone in milk with and without preservative were also highly correlated (r=0.96).

Monitoring of milk progesterone concentrations from a week after calving through to 4 weeks after insemination showed that the length of the postpartum acyclic period (PPAP) was not affected by season. There was also no significant relationship between the length of PPAP and age, parity, milk yield, days open, body weight and body condition after calving. One factor that did lengthen the PPAP was the occurrence of a post-partum transient progesterone rise (PTPR) prior the first normal oestrous cycle. The observation of oestrus (standing heat behaviour) by experienced herdsmen observing cows twice daily was also recorded in the study. In the period between calving through to insemination only 58.5% of ovulations were accurately detected when checked against milk progesterone levels.

Two trials were carried out to determine the effect of GnRH analogue (Fertagyl R, Intervet, Australia: Pty. Ltd) on fertility and cycle lenth of Cows which failed to conceive after insemination. An intra-muscular injection of 100 μg Fertagyl R on day 14 after insemination significantly increased (p<0.05) the levels of plasma progesterone within 5 hours. The interval from insemination to return to oestrus of cows which failed to conceive did not alter (p>0.5) after treatment, and conception rates were not significantly affected.

Pregnancy diagnosis at 21 to 24 days after insemination using milk progesterone concentrations was highly accurate. The use of discriminant analysis for setting the cut off levels of milk progesterone which separated pregnant and non-pregnant cows improved the sensitivity of this pregnancy test. The highest accuracy was 97.2% (69/71) for pregnant and 92.1% (47/51) for non-pregnant cows at 23 days after insemination. Factors such as shortened or prolonged oestrous cycle after failing to conceive, embryonic mortality, insemination at the wrong time or oestrus not being accurately detected caused false positive results. A transient decrease in milk progesterone levels in some cows around 21-24 days of pregnancy caused some false negatives results.

The last experiment concerned the investigation of fertility problems in 4 dairy herds, using monthly milk samples for assaying progesterone and combining this information with results of reproductive examinations on monthly Herd Health visits. Milk progesterone from individual cows with abnormal ovarian structures helped distinguish between follicular and luteal cysts. The herd incidence of cows with high and low progesterone levels at monthly sampling helped define periods of protracted postpartum anoestrus through the year.

Item Type: Thesis (Masters by Research)
Murdoch Affiliation(s): School of Veterinary Studies
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Williamson, Peter
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