Control and induction of ovulation in cattle
Roche, J.F.; Ireland, J.; Mawhinney, S.
Journal of Reproduction and Fertility. Supplement 30: 211-222
1981
ISSN/ISBN: 0449-3087 PMID: 6962842 Document Number: 176747
A review, with some fresh experimental studies. Treatment with progesterone-impregnated coils for 14 days was required to obtain precise onset of oestrus in heifers and beef cows. With 7, 9 or 12 days of progesterone treatment, a luteolytic agent in the form of PG or oestradiol benzoate had to be used. Fertility was normal after treatments lasting 7, 9 or 12 days, but fertility after a 14-day treatment required further testing. The progesterone coil was not effective in maintaining luteal-phase levels of progesterone throughout a 12-day treatment, and increasing the concentration of progesterone in the coil from 4 to 20% was not effective in elevating the progesterone concentrations in blood. When progesterone concentrations dropped below approx. 1.5 ng/ml, the basal level of LH began to rise before removal of the coil. A two-fold rise in the basal level of LH was observed following the removal of the progesterone coil. This early rise in LH was absent in cows which did not ovulate after they were given a 12-day progesterone treatment, plus GnRH 24-36 h after removal of coils to induce the main LH peak. Absence of this early rise suggests that the frequency and amplitude of episodic LH release were inadequate in the postpartum anovulatory period. Ovariectomy in the early postpartum period was not followed by an abrupt LH release.