An adaptation of the technique described by Johansson (1969), whereby progesterone was measured by a rapid competitive protein binding technique, has been used to determine the progesterone levels in the peripheral plasma of the cow (Edqvist, Ekman, Gustafsson & Åström, 1970). The purpose of this paper is to report the usefulness of the same technique for the measurement of progesterone levels in the peripheral blood plasma of the sow during the oestrus cycle.
Two sows of the Swedish Landrace Breed, fed on a commercial pig diet with unlimited water supply, were used. Sexual receptivity was checked twice a day with a boar. The first day of receptivity was considered to be the first day of the oestrous cycle.
About 1 ml of blood was collected daily from an ear vein into