Effect of late pregnancy, parturition and early lactation on T3, T4 and cortisol level of heifers and cows

الملخص EN

The present study was carried out in the Al-Dujalah Cows Station which is located in Wasit governorate, Iraq.

From 305 crossbred cows (Holstein x Friesian breeds), thirty six heifers (2.5-3.5) years old and thirty six multiparous cows (5-7) years old at different physiological conditions.

The heifers and cows were divided into six equal groups depending on their physiological conditions as follows, group 1 : Non-pregnant heifers (control), group 2 : (Heifers in 7th month of pregnancy), group 3 : (Heifers in 8th month of pregnancy), group 4 : (Heifers in 9th month of pregnancy), group 5 : (Heifers at 1-4 hours of parturition), group 6 : (Heifers in first month of lactation).

The multiparous cows were divided as that of heifers.

The blood samples (5ml) were collected from Jugular vein at 2 weeks interval during pregnancy, at parturition (1-4 hours after parturition) and first month of lactation and deposited into plastic tube without anticoagulant to obtaining the serum samples for hormonal analysis.

The study revealed the following results: A significant increase (p≤0.05) in serum (T4) level was recorded in last month of pregnancy in both heifers and cows compared with control and other studied groups and a significant decrease in T3 level was observed in 7th month of pregnancy, at parturition and first month of lactation in cows while there was a significant increase in T3 level was recorded in 9th month of pregnancy in heifers compared with control and other studied groups.

A significant increase (p ≤ 0.05) in serum cortisol level was recorded in first month lactating animals compared with control and other studied groups in both heifers and cows, and a significant increase in serum cortisol level was observed in control, 8th and 9th month of pregnancy and at parturition in cows compared with that of heifers.