The present studies were conducted to check the effects of acute ram introduction into a flock of anestrus ewes in Virginia. Ewes were bled via jugular venipuncture twice weekly and serum samples were radioimmunoassayed for progesterone (P4) content as an indicator of estrous activity. All rams were fitted with crayon equipped marking harnesses for use as an indicator of mating behavior in ewes. The first study tested the effects of introduction of vasectomized rams into a flock: of' 50 Dorset (D) and 50 Hampshire (H) purebred ewes in either May or June. More D ewes ovulated (96% vs 72% for H ewes) and mated (80% vs 20% for H ewes) in May. Of ewes which mated in May 65% D but no H ewes continued to cycle in June after removal of rams. Of ewes exposed to rams in June no difference among breeds was observed in percentage of ewes ovulating but more D ewes (72%) mated than H ewes (44%). Twenty-four percent of D but no H ewes cycled continuously throughout the 68 d or the study. Lambing date significantly affected mating behavior in H but not D ewes.

The second study tested the effects of ram breed on incidence of mating and subsequent lambing in Rambouillet x Q Suffolk ewes In June and July of 1984 and 1985. Ewes were Q pre-exposed to either confined Suffolk (S) or Dorset (D) Q yearling rams or no (N) ram for 2 wk prior to breeding by Q either S or D rams. Lambing date was significantly affected by breeding treatment in 1984 and by pre-exposure treatment in 1985. Sixty-three percent of the ewes lambed in 1984 while 65% lambed in 1985.