The ram effect on the reproductive cycle of the springbok ewe (antidorcas marsupialis)

Abstract

Plasma progesterone concentrations were used as a measure to determine the "ram effect" on nine cycling springbok ewes. Blood was collected biweekly, prior to and after ram introduction. Ewes were subjected to the ram for a period of forty two days. Blood was analysed for plasma progesterone by means of radioimmunoassays. No significant changes in the plasma progesterone concentrations were detected. Superficially, a reduction in the variation of the follicular phase of the ewes oestrous cycle was noted for before- to after ram introduction. However, possibly because of a too small sample size, no statistical significance was found. It is suggested that the "ram effect" on aseasonal cycling species may only have a synchronisation effect (reduction in the variation of time between the follicular phase of females) but more individuals should be used in future experiments to make any clear and definite conclusions. Furthermore other hormones such as e.g. luteinizing hormone, which may be less affected by translocation and handling stress, should also be used to determine the "ram effect" on aseasonally breeding wild ungulates.