Peripheral plasma levels of progesterone in Nigerian Zebu cows following synchronization of oestrus with Prostaglandin F 2 alpha analogue (dinoprost tromethamine)

Abstract

The luteolytic effect of Prostaglandin F 2 alpha (PGF 2α) was studied by measuring plasma progesterone levels in 30 Bunaji and Sokoto Gudali (Zebu) cows. Two intramuscular (i.m.) injections each of 25 mg of the analogue (Dinoprost tremethamine) were given 11 days apart and blood samples for plasma were collected daily beginning from first injection up to 7 days after the second injection of PGF 2α or up to 30 days after artificial insemination (A.I). Mean progesterone levels on the day of first injection were 4·1 + 0·3 and 0·6 ± 0·2 nanograms per millilitre (ng/ml) for cows in luteal and follicular phases respectively. Luteolysis was complete within 24–48 h of injection as confirmed by plasma progesterone levels. Cows in luteal and follicular phases showed standing oestrus 75·1 ± 2·1 h and 55·2 ± 12·2 h after PGF 2α injection. Partial or incomplete luteolysis were also observed in 2 cows. Cows showing standing oestrus after a second injection of PGF 2α were artificially inseminated 12 h after the onset of oestrus. Six out of 12 cows (50%) were diagnosed pregnant by rectal palpation at 60 days post-insemination. Plasma progesterone levels in pregnant cows remained elevated (2–15 ng/ml) and did not drop below 2·0 ng/ml following attainment of peak levels. Appreciable levels (1.0 ng/ml) of progesterone were first detected 5–6 days postinsemination in inseminated cows. Of those that were later diagnosed non-pregnant, however, there was a cyclic progesterone pattern which culminated in complete luteolysis about 18 days after the infertile insemination. The results indicate that intramuscular administration of 25 mg of PGF 2α per cow during the luteal phase of the oestrous cycle of Zebu cows shortens the secretory lifespan of cyclic corpus luteum, and that plasma progesterone assays may be valuable in assessing the reproductive performance of Zebu cows indigenous to Nigeria.