CONCENTRATION OF BLOOD-SERUM THYROID-HORMONES DURING LATE PREGNANCY, PARTURITION AND EARLY LACTATION OF CROSSBRED COWS

Six crossbred cows (Gir crosses with Holstein-Friesian) were studied f or thyroid function around parturition. They were in advanced stage of pregnancy, the gestation period ranged from 276 to 287 days with an a verage 280 +/- 2 days. Blood samples were collected by jugular venipun cture from each cow between 8.00 AM and 9.00 AM twice weekly from 26 t o 6 days before parturition, once daily from 6 days before to 5 days a fter parturition and further twice weekly up to 15 days postpartum. Co nsiderable variations in triiodothyronine (T-3) thyroxine (T-4) and T- 4:T-3 ratio existed between individual animals. Both triiodothyronine and thyroxine showed decreasing trend towards parturition, reaching th e lowest concentrations on the day before parturition. The values incr eased on the day of parturition and declined after calving. The T-4:T- 3 ratio followed the pattern of T-3 and T-4 profile in the blood with decreasing trend towards parturition reaching the lowest value 1 day b efore the parturition. The ratio rose on the day of parturition. The d ecrease in the thyroid hormones around parturition as observed in the present study might he due to alteration in cardiac output and increas ed blood volume.