Hossein Hamali - Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tabriz,Tabriz- Iran
Javad Jafari - Department of Theriogenology, Faculty of Veterinary Medicine, University of Tehran, Iran, and Graduated of Veterinary Medicine, University of Tabriz, Tabriz, Iran
Ezzatullah Fathi - Department of Clinical Sciences, Faculty of Veterinary Medicine, University of Tabriz, Iran

The use of dexamethasone in many diseases such as ketosis, drug and food allergies and septic shock is pointed out in cows. Dexamethasone using in pregnant cows is limited due to it, s abortive effect. On the other hand dexamethasone does not always cause abortion. So the aim of our study was to detect the exact period that we can use the dexamethasone in the pregnant heifers. To achieve this purpose, we selected ۴۰ Holstein heifers from farms with the same nutritional and welfare systems. After confirmation of conception with ultrasonography ۳۰ days after mating, Holstein heifers divided in to two completely randomized groups. In group A (n = ۲۰, treatment), ۳۰ mg dexamethasone were administered intramuscularly to the cows every ۱۵ days until the heifers started abortion. In group B (n = ۲۰, control) ۱۵ cc of normal saline were injected every ۱۵ days. Blood samples were taken ۲۴ hours before the injection and ۷۲ hours after injection then progesterone levels were measured. The exact time of reduction in progesterone levels in the blood were recorded. The results was analyzed by using Chi-Square statistical methods (on the rate of abortions) and t-test on progesterone changes before and after dexamethasone injection and using software version ۲۲, Inc., Chicago, IL, USA SPSS. Based on our findings, dexamethasone’s first effect was at ۷۵ days of pregnancy (p<۰.۰۵), so it can be used up to day, s ۷۵ of pregnancy. Dexamethasone’s effect can be attributed to changes in the concentration of progesterone, estrogen and number of their receptors during pregnancy.

Heifer, Progesterone, Abortion, Pregnancy, Dexamethasone