Synchronization of estrus in sheep using progestagen and inseminating with chilled semen during the breeding season

Abstract

The efficiency of synchronization following the use of halved or whole (60 mg) MAP sponges and 300 IU PMSG during the breeding season was evaluated using 111 Merino ewes. Artificial insemination was performed with chilled semen (stored as 15 °C for 3 h) at 55 h following sponge 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, respectively) 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, respectively) was not significantly different in the groups. A high percentage of MAP was still present in the whole (76.6%) and halved (49.3%) sponges following withdrawal after 14 days. The mean serum progesterone concentration during the estrous period was higher ( P < 0.01) in the control group. No significant difference was found in the peak serum LH concentrations and the position of the LH peak relative to estrus. 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 MAP sponges (54.8%). Similarly the lambing rate was also higher ( P < 0.01) for the halved sponges and control group, compared with the whole sponges (106.8 vs 104.9 vs 85.9%, respectively). Halving of 60-mg MAP sponges is warranted in the breeding season and fertility results obtained with chilled semen are satisfactory.