The influence of prostaglandin analogue and PMS treatment on the lambing performance of Libyan fat-tailed ewes

Of 243 Libyan fat-tailed ewes 93 were non-treated controls (C group), the remaining ewes received two intramuscular injections of prostaglandin F2α analogue (PG) 10 days apart. Thirteen days after the second PG injection these ewes were divided into three equal groups and received: no treatment (group S0), 500 i.u. pregnant mare's serum (PMS) (group S500) and 1000 i.u. PMS (group S1000).Treatment with PG concentrated lambing into a 14-day period with maximum incidence of lambing (44·6% of lambings in treated ewes) on the 7th, 8th and 9th days. During the synchronized period 79·1% of the treated ewes lambed compared to 56·5% of the controls. However, within the treated groups PMS treatment reduced the incidence of lambing during the whole observation period (95·7% in S0, 93·8% in S500 and 85·4% in S1000) due mainly to reduction of lambing during the sychronized lambing period (91·3% in S0, 83·3% in S500 and 64·6% in S1000).The number of lambs born/ewe put to the ram (C 0·94, S0 1·09, S500 1·27 and S1000 1·19 lambs) and the number of lambs born/ewe lambing (C 1·07, S0 1·14, S500 1·36 and S1000 1·39 lambs) increased with PMS treatment. The prolonged or continuous breeding activity of fat-tailed sheep would appear to provide a greater opportunity for the use of PG as an aid to management.