Studies on the efficiency of mating in the sheep I. The effect of paddock size and number of rams

Abstract

A factorial experiment is described in which seventy-two spayed crossbred ewes were used in four successive tests at intervals of 15 days in a study of factors affecting the detection of oestrus. Variates introduced in each test were: (a) number of rams to eighteen ewes (one or three); (b) size of mating paddock (17 acres or ⅕ acre); (c) dose of oestrogen (oestradiol benzoate, ODB: 10·0, 15·6, 24·4 μg.).All ewes were primed with progesterone for 12 days prior to ODB injection and joining. The number of ewes detected in oestrus and the mean number of ewes served per ram were recorded.In the four successive tests, thirty-two, fortyseven, forty-six and forty-one ewes were served (P < 0·05). Three rams working together detected ninety-eight ewes in oestrus while rams working individually detected sixty-eight (P < 0·001). Size of mating paddock had no significant effect (17 acres, 89; Jacre, 77).The mean number of ewes marked per ram when used singly was indistinguishable from the mean number when rams were in groups of three (8·5 and 9·3). This resulted in multiple coverage of oestrous ewes when group joined (average 2·3 rams per ewe).