Comparison of 6-day progestagen treatment with Chronogest® CR and Eazi-breed™ CIDR® G intravaginal inserts for estrus synchronization in cyclic ewes

Abstract

The aim of this study was to compare the efficacy of two different short-term progestagen treatments for estrus synchronization in cyclic ewes. A total of 292 ewes of 3 flocks (A–C) on different farms were treated for 6 days with Eazi-breed™ CIDR® G (n=145) or Chronogest® CR (n=147) vaginal inserts in combination with 0.125mg Cloprostenol and 300IU eCG at device removal. Blood samples were taken for progesterone (P4) determination at insert application and removal as well as 14 days later. One day after insert removal rams fitted with marking harnesses were joined to ewes for 35 days and marked ewes recorded daily. Lambing data were recorded and fertility to first service period and overall assessed. Results show that 24–96h after insert removal 98.8% and 89.4% of the synchronized ewes in the flocks B and C were in estrus. Estrus response was not affected by the type of progestagen treatment and was lower (P<0.05) in nulli- (82.1%) than in pluriparous (97.5%) ewes. Type of progestagen treatment did not affect fertility, but flock and parity influenced the percentage of ewes that lambed as well as the lambing rate. Overall more ewes (P<0.001) lambed in flock A compared to flocks B and C (93.0 vs. 72.5 and 59.1%). In nulliparous animals the percentage of ewes that lambed was higher to the first service (P<0.05) period but lower (P<0.001) to the overall service period compared to pluriparous animals (51.5% vs. 49.3% and 64.7% vs. 84.2%). Lambing rates were higher in flock A than in flocks B and C to first service period and overall (1.3±1.4, 0.9±1.0, and 0.7±1.0, P<0.01 and 1.9±1.1, 1.3±0.9, and 1.0±1.0, P<0.001) and in nulliparous overall lower than in pluriparous ewes (1.1±1.1 and 1.6±1.1, P<0.01). Serum P4 concentrations measured 14days after insert removal were higher in the Chronogest® CR than in the Eazi-breed™ CIDR® G group (6.8±4.1ng/mL vs. 5.7±3.3ng/mL). Ewes of flock A had higher P4 values compared to ewes of flocks B and C (8.3±4.1ng/mL vs. 4.5±1.5ng/mL and 3.8±1.7ng/mL) and nulliparous lower P4 concentrations than pluriparous ewes (4.5±2.2ng/mL vs. 6.7±4.0ng/mL). In conclusion, a 6-day treatment with Chronogest® CR and Eazi-breed™ CIDR® G with prostaglandin and eCG at insert removal resulted in high estrus response and similar fertility in cyclic ewes.