Antiprogesterone, RU 486, facilitates parturition in cattle

Area of Science:

• Veterinary Medicine
• Reproductive Biology
• Endocrinology

Background:

• Parturition induction in cattle is crucial for managing calving intervals and improving calf survival.
• RU 486, a potent progesterone antagonist, has shown potential in disrupting pregnancy and inducing labor.
• Relaxin's role in parturition suggests a potential synergistic effect with progesterone antagonists.

Purpose of the Study:

• To evaluate the efficacy of RU 486, alone or combined with relaxin, in inducing parturition in late-pregnant cattle.
• To assess the impact of this treatment on calving time, calf characteristics, and delivery complications.
• To monitor hormonal changes, specifically progesterone levels, following treatment.

Main Methods:

• Cross-bred beef cattle in late pregnancy were randomly assigned to three groups: RU 486 alone, RU 486 plus relaxin, or control (vehicle).
• RU 486 was administered intramuscularly, with relaxin administered subcutaneously on a specified day prior to expected term.
• Indwelling jugular vein cannulas were used for serial blood sample collection to monitor progesterone and RU 486 levels.

Main Results:

• Parturition was significantly induced, occurring 53-55 hours post-treatment in RU 486-treated groups compared to 210 hours in controls.
• Calves from treated groups were vigorous, with reduced birth weights (32-33 kg) versus controls (38 kg).
• No incidence of dystocia was observed in treated groups; placenta delivery times were comparable across all groups.

Conclusions:

• RU 486, alone or with relaxin, provides precise control over parturition timing in late-pregnant cattle.
• This treatment facilitates calving, potentially increasing neonatal calf survival by mitigating dystocia and other complications.
• Hormonal monitoring confirmed RU 486's rapid suppression of progesterone, initiating the calving process.