Short-term progestagen treatment in ewes during the breeding season

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To characterize the efficiency of oestrus synchronization with short-term progestagen treatment (stFGA), 20 Ile de France (IF) and 19 Churra da Terra Quente (CTQ) ewes were used during the mid-breeding season. At day 0 (D0), a 40 mg FGA sponge was inserted in all animals and 120 µg cloprostenol was injected. Five days later (D5), all sponges were removed and ewes were divided into two groups: group A (10 IF and 10 CTQ), treated with eCG (250 UI) at sponge withdrawal and group II (10 IF and 9 CTQ), without eCG. Blood samples were taken biweekly for progesterone (P4) determination and four intact rams with harness markers identified the onset of oestrus (first mount). All ewes were cyclic at D0 but oestrus was detected only in 32 (82%), with no difference (p > 0.05) between group or breed. The remaining seven ewes had lower P4 (< 0.5 ng/ml) betweem D-2 and D0. The interval between sponge withdrawal and onset of oestrus was 40.5 ± 9.6 h, with no difference between treatment or breed. However, for IF ewes, this interval tended to be shorter (P = 0.10) than CTQ ewes (37.8 ± 10.1 h vs 43.3 ± 8.6 h). The pregnancy rate (75%) and prolificacy (1.38) were also similar between treatments and breeds. The stFGA was a good method to synchronize the oestrus in sheep during breeding season: pregnancy rate and prolificacy were not affected by eCG administration.