Concentration of blood serum thyroid hormones during late pregnancy, parturition and early lactation of crossbred cows

Abstract

Six crossbred cows (Gir crosses with Holstem-Friesian) were studied for thyroid function around partuntion. They were in advanced stage of pregnancy, the gestation period ranged from 276 to 287 days with an average 280 ± 2days, Blood samples were collected by Jugularvenipuncture from each cow between two AM and 9.00 AM twice weekly from 26 to 6 days before parturiyion, once daily from 6 days before to 5 days after parturition and further twice weekly up to 15 days postpartum. Considerable variations in triiodothyronine (T₃),thyroxine(T₄)and T₄ :T₃ ratio existed between individual animals, Both triiodothyronine and thyroxme showed decreasing trend towards parturiuon, reaching the lowest concentrations on the day before partutition. The values increased on the day of parturition and dechined after calving. The T₄ : T₃ ratio followed the pattern of T₃ and T₄ profile in the blood With decreasing trend towards parturition reaching the lowest value 1 day before the parturition. The ratio rose on the day of parturition. The docrease in the thyroid hormones around parturition as observed in the present study might be que to alteration in cardac output and increased blood volume.