Reproductive responses of beef heifers and cows to exogenous progesterone administered in silastic coils,oestradiol benzoate and pregnant mare serum gonadotropin

The aim of this study was to investigate a Progesterone Releasing Intravaginal Device, Oestradiol benzoate and PMSG combined treatment in 81 suckling charolais cows and 56 heifers of various breeds. The former were young primiparous cows aged 2 years and treated at a means of 43 days postpartum. Most of the heifers ($\text{44}\text{56}$) were not cycling and were believed to be prepuberal.In non-cycling females, the treatment induced ovulation in 98.5% of the cows and 78 to 100% of the heifers according to breed. In those females in which ovulation was induced, pregnancy rates determined by rectal palpation were 46.9% for the cows and 66.7% for the heifers. When taking into account all treated females including those with lost Progesterone Releasing Intravaginal Devices (5.8%) and those not ovulating, the pregnancy rates determined by rectal palpation 3 to 5 months after artificial insemination were 40.7% for the cows and 52% for the heifers.