SYNCHRONIZATION OF ESTRUS IN SHEEP USING PROGESTAGEN AND INSEMINATINGWITH CHILLED SEMEN DURING THE BREEDING-SEASON

The efficiency of synchronization following the use of halved or whole (60 mg) MAP sponges and 300 IU PMSG during the breeding season was ev aluated using 111 Merino ewes, Artificial insemination was performed w ith chilled semen (stored as 15 degrees C for 3 h) at 55 h following s ponge withdrawal in the progestagen treated ewes and at 12 h following the onset of natural estrus in the control group. Estrous occurrence from time of sponge withdrawal, the interval from sponge withdrawal to estrus (mean of 30.5 vs 27.5 h for the whole and halved sponges, resp ectively) and the duration of the induced estrous period (mean of 25.1 vs 28.3 vs 35.0 h for the whole, halved sponges and control groups, r espectively) was not significantly different in the groups. A high per centage of MAP was still present in the whole (76.6%) and halved (49.3 %) sponges following withdrawal after 14 days. The mean serum progeste rone concentration during the estrous period was higher (P < 0.01) in the control group. No significant difference was found in the peak ser um LK concentrations and the position of the LH peak relative to estru s. The conception rate was higher(P < 0.01) in the halved sponges and the control (70.5 and 64.0%, respectively), compared with the whole MA P sponges (54.8%). Similarly the lambing rate was also higher (P < 0.0 1) for the halved sponges and control group, compared with the whole s ponges (106.8 vs 104.9 vs 85.9%, respectively). Halving of 60-mg MAP s ponges is warranted in the breeding season and fertility results obtai ned with chilled semen are satisfactory. (C) 1997 Elsevier Science B.V .