Relationship between the effect of human chorionic gonadotropin treatment on the fifth day after artificial insemination and ovarian ultrasonographic findings and blood nutritional metabolic factors in dairy cows

The objective of the present study was to determine the ovarian ultrasonographic findings and metabolic factors that influence the effect of human chorionic gonadotropin (hCG) treatment on the fifth day after artificial insemination (AI) in dairy cows. Thirty-seven lactating Holstein cows were assigned to two groups: the hCG group (n = 25), which received 3000 IU of hCG intramuscularly on Day 5 after AI (day of AI = Day 0), and the control group (n = 12), which received no treatment. Ovarian ultrasonography measured luteal tissue area (LTA), luteal blood flow area (LBF), relative LBF (= LBF/LTA), and dominant follicle area on Day 5. Blood tests measured plasma insulin-like growth factor-I, insulin, and metabolite concentrations on Day 5 and plasma progesterone concentrations on Days 5 and 7. LBF was greater in pregnant cows than in non-pregnant cows, and plasma Glu concentration was lesser in pregnant cows than in non-pregnant cows, but in both cases there was no interaction between group and pregnancy outcome. For plasma insulin concentration, there was an interaction between group and pregnancy outcome, with pregnant cows in the hCG group having lesser concentrations than the other groups. Logistic regression analysis showed that group and the interaction between group and plasma insulin concentration were associated with pregnancy outcome. These results suggest that the effect of hCG treatment on Day 5 after AI is related to plasma insulin concentration and is more effective in cows with lesser plasma insulin concentrations.