The Effect of PMSG Treatment on Pregnancy Rates in Synchronized Heifers using Norgestomet Ear Implants

This study was carried out in heifers, which were administered with norgestomet implants for estrus synchronization, with an aim to determine the effect of PMSG, administered to the animals on the day of the removal of the implants, on pregnancy rates. A hundred Holstein heifers, aged 15-16 months, constituted the material of the study. In this study all of the heifers were administered ear implants containing 3 mg norgestomet subcutaneously on the external surface of the ear. Following the insertion of the implants, on the same day, all of the heifers were intramuscularly administered 10 mu g buserelin acetate. After a period of 10 days, the implants were removed. Two days prior to the removal of the implants, the heifers were injected with 500 mu g of cloprostenol by intramuscular route. On the day of the removal of the implants, the animals were randomly assigned to two groups which comprised an equal number of heifers. The heifers included in Group I (n=50) were injected with 400 IU pregnant mare's serum gonadotropin (PMSG) by intramuscular route, whilst the heifers included in Group II (n=50) were not subjected to any treatment. At the 56th hour following the removal of the implants, all heifers were inseminated regardless of the presence of oestrus signs. The pregnancy diagnosis was carried out on 35th days after insemination. The pregnancy rates achieved in Groups I and II were determined as 86% (43/50) and 54% (27/50), respectively (P<0.001). It was concluded that, in heifers, which were synchronized with subcutaneous norgestomet implants, the addition of PMSG on the day of the removal of the implants increased the pregnancy rates.