Effect of progestagen and PMSG on oestrous synchronization and fertility in Dorper ewes during the transition period

An oestrous synchronization study was conducted on 202 Dorper ewes kept under extensive veld conditions of South Africa, during the transition period from the natural breeding to the anoestrus season. Two types of intravaginal progestagen sponges, namely MAP (60 mg) (n = 102) and FGA (40 mg) (n = 100), three times of PMSG administration relative to sponge withdrawal (24 h before (n = 59), at (n = 56) or 24 h after (n = 57)) and two routes of PMSG administration (intramuscular (n = 87) or subcutaneous (n = 85)) were compared regarding synchronization efficiency (oestrous response, time to onset of oestrus and duration of oestrus) and fertility (pregnancy, lambing, and fecundity rates) following AI with 0.1 ml fresh diluted semen. There were no significant differences in terms of oestrous response, time to onset of oestrus and the duration of induced oestrus due to differences in the type of progestagen sponges or time and route ofPMSGadministration. The overall pregnancy, lambing, and fecundity rates were 72.3, 91.1, and 126.0%, respectively. There were no significant differences in pregnancy, lambing, and fecundity rates between ewes treated with MAP and FGA sponges (70.6, 85.3, and 120.8% versus 74.0, 97.0, and 131.1%, respectively). However, within treatment, pregnancy, lambing, and fecundity rates were significantly (P < 0.01) higher in ewes administered 300 IU PMSG 24 h prior to (78.0, 115.3, and 147.8%, respectively) or at sponge withdrawal (75.0, 94.6, and 126.2%, respectively), compared to those administered 24 h after sponge withdrawal (70.2, 73.7, and 105.0%, respectively) or those not injected with PMSG (60.0, 70.0, and 116.7%, respectively). Both MAP and FGA sponges could be used to synchronize oestrus in Dorper ewes during the transition period from breeding to anoestrus. Administration of 300 IU PMSG preferably 24 h prior to or at progestagen sponge withdrawal is essential to obtain better fertility rates at the induced oestrus and following AI. The subcutaneous administration of PMSG is preferable to intramuscular administration as it resulted in higher fertility rates and litter sizes. © 2004 Elsevier B.V. All rights reserved.