Effect of Progesterone Treatment on Synchronising Oestrus during Non-Breeding Season in South African Merino Ewes

Abstract

The aim of the study was to compare the effect of short and long-term progesterone treatment and their combination with or without equine chorionic gonadotropin (eCG) on oestrous response and hormonal profiles during non-breeding season. Seventy-six (76) Merino ewes aged between 2–5 years were allocated into two groups, 36 for short-term and 40 for long-term progesterone treatments. In the short and long-term progesterone treatment groups, controlled internal drug release devices (CIDR) were inserted for 11 and 14 days, respectively. At withdrawal of CIDR, half of each group were injected intramuscularly with 300 IU of eCG. Blood samples were collected to measure the level of progesterone and oestradiol. Ewes treated with both short or long-term progesterone combined with or without eCG resulted in the same oestrus response, onset of oestrus and duration of oestrus. The levels of progesterone hormone were the same at CIDR insertion, and removal and 48 hours post CIDR removal. However, oestradiol hormone was significantly higher at CIDR removal and 48 hours post CIDR removal than at insertion in all treated groups. Therefore, it can be concluded that oestrous synchronisation protocols of both short and long-term progesterone combined with or without eCG during non-breeding season can be used to synchronise oestrus during non-breeding season.