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.
