Plasma progesterone concentrations during the oestrous cycle and following fertile and non-fertile inseminations of Zebu heifers

Abstract

Two separate studies were conducted to determine the profiles of plasma progesterone concentrations during the oestrous cycle and early pregnancy in Zebu cattle. Thirty-three Bunaji (Zebu) heifers aged between three and four years were used. In experiment 1, blood samples were collected from 17 heifers by jugular vein puncture at two-day intervals during the oestrous cycle preceding AI. Further blood samples were collected up to 30 days after AI or until the heifers came in heat. In experiment 2, 16 heifers were treated with 25 mg PGF 2α during mid-luteal phase. All heifers were inseminated (AI) at observed oestrus and pregnancy diagnosis done at 60 days after AI. Blood samples for plasma were collected as described earlier beginning from the day of injection up to 30 days after AI or until they came in heat. All plasma samples were analysed for progesterone by radioimmunoassay. Plasma progesterone levels increased from day 4 after oestrus and reached a peak of about 3 ± 2·5 ng/ml on day 10 and then declined gradually thereafter to non-detectable levels on day 18. Plasma progesterone concentrations for the pregnant and non-pregnant heifers were compared up to day 16 post AI. The oestrous cycle length following non-fertile inseminations (23·7 ± 1·8 days) was significantly longer ( P < 0·05) than that preceding AI (20·0 ± 2·3 days). During the period under comparison, plasma progesterone values were also generally higher (though not significant) for the pregnant than for the non-pregnant heifers following synchronization of oestrous and AI. The results suggest a normal pattern of progesterone profile during the oestrous cycle and comparatively higher progesterone levels in pregnant than in inseminated non-pregnant Zebu cattle during early pregnancy.