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| The effect of treatment with a gonadotrophin-releasing hormone (GnRH) analogue-Buserelin acetate, human chorionic gonadotrophin (hCG) and exogenous hydroxy-progesterone caproate on plasma progesterone profile and conception rates was investigated in 44 repeat breeding dairy cattle. Repeat breeding dairy cows on Day 5 post artificial insemination were randomly assigned to four groups: control (no treatment, n=11), Inj GnRH analogue (buserelin acetate, 20µg, n=11), Inj hCG (3000 IU, n=11), or Inj hydroxy progesterone caproate (500 mg, n=11) administered once IM. Progesterone concentration (ng/ml) was determined in plasma of cows on Day 0, 5, 12 and 19, and pregnancy diagnosis was undertaken on Day 60 by rectal palpation. The plasma progesterone concentrations on the Day of insemination were not significantly different between the treatment groups. The plasma progesterone concentration increased significantly (P<0.01) on Day 5 in all cows in all groups. On Day 5 the differences between different treatment groups were non significant. The plasma progesterone concentrations one week after treatment i.e. on Day 12 were significantly higher compared to values on Day 5 in treatment GnRH and treatment hCG (P<0.01). In progesterone treatment and untreated control cows although the plasma progesterone concentrations increased from 2.12±0.25 ng/ml on Day 5 to 4.99±0.23 ng/ml on Day 12 in progesterone treatment and 2.02±0.08 ng/ml on Day 5 to 4.24±0.23 ng/ml on Day 12 in control cows, the differences were non significant. GnRH and hCG treatments increased the plasma progesterone and this probably supported the higher conception rates in these groups. On Day 19 the plasma progesterone concentrations were significantly higher (P<0.01) in all groups compared to progesterone profile on Day 0 and significantly higher (P<0.01) compared to concentrations on Day 5 in GnRH and hCG treatments. When compared to concentrations on Day 12 the progesterone concentration decreased significantly (P<0.01) in hCG treated cows on day 19. Transrectal palpation after treatment in treated cows revealed the formation of accessory corpus luteum in 27.27% cows in GnRH treated, 0% in progesterone treated, and 36.36% in hCG treated cows. The pregnancy rates were highest in hCG treatment (45.45%) followed by GnRH (36.36%) and progesterone (27.27%) compared to untreated control cows (18.18%). It was concluded that the hormonal therapies on Day 5 post insemination increase the plasma progesterone concentration and conception rates in repeat breeding dairy cattle with hCG treatment being the best.

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