the reproductive tract, at known stages of the oestrous cycle and pregnancy. The blood (about 150 ml) was drawn into vessels containing sodium citrate and.
EARLY EFFECT OF CONCEPTUS ON PLASMA PROGESTERONE LEVEL IN THE COW M.
H. R. LINDNER
Department of Reproduction, The Veterinary Research Institute, Beth-Degan, Israel, and Department of Biodynamics, Weizmann Institute of Science, Rehovoth, Israel (Received 31st August 1967) Progesterone levels in jugular venous blood are being measured by us in cycling (unmated) and inseminated (pregnant or non-pregnant) cows as part of a comparative study of cows with normal and difficult breeding histories. Hawk, Wiltbank, Kidder & Casida (1955) reported a high incidence of embryonic death in cows during the period 16 to 25 days after insemination. The 3rd week of gestation may indeed be a critical phase in the regulation of luteal function, since towards the end of this week regression of the corpus luteum normally occurs in the absence of a conceptus. This note records that in a herd of normal Friesian cattle with a cycle length of 21\m=.\2days \m=+-\1\m=.\5s.d. the presence of a conceptus in the uterus first exerted a significant effect on the peripheral plasma progesterone level on the 19th day after insemination. Samples of blood were collected between 07.30 and 08.00 hours from the jugular veins of cows free from venereal infection or demonstrable lesions of the reproductive tract, at known stages of the oestrous cycle and pregnancy. The blood (about 150 ml) was drawn into vessels containing sodium citrate and cooled rapidly to 4\s=deg\C. The plasma was separated by centrifugation at 4\s=deg\C and stored at \p=m-\18\s=deg\C until analysis, performed usually within 2 weeks. Plasma samples (80 ml) were extracted as described by Lindner, Lunenfeld & Shelesnyak (1967), and the concentration of progesterone in these extracts was determined by the method of Lindner & Zmigrod (1967), which is based on sequential paper- and gas-chromatography with a hydrogen-flame detector, and use of a radio-active internal recovery standard. Jugular venous blood collected from a cow 7 days after ovariectomy con¬ tained a detectable, if very low, concentration of progesterone (0-17 µg|100 ml) ; 3 weeks after the operation the progesterone level was undetectable (