Previous work has shown that although the ovaries of multiparous sows are quiescent throughout lactation (McDonald, 1980; Edwards, 1982) there are episodes of oestrogen activity in the peripheral circulation which are both highly variable and at very high concentrations (Varley and Foxcroft, 1989). The suspicion is that the source of this oestrogen is the adrenal gland although it is also possible that body fat stores are capable of being involved in this. Any treatment causing adrenal regression should therefore reduce the incidence of oestrogen episodes in the peripheral circulation.

An experiment was therefore carried out at Leeds University to investigate the use of an orally active progestogen, allyl-trenbolone, which is routinely used in gilts and sows for the control of oestrous cycles, on the steroid hormone status and reproduction in multiparous sows.