Norgestomet implants maintain pregnancy in ovariectomized heifers

Area of Science:

• Reproductive endocrinology in livestock
• Veterinary obstetrics and gynecology

Background:

• Hormonal synchronization protocols are crucial for efficient artificial insemination (AI) in cattle.
• Norgestomet implants are used for estrus synchronization, but their long-term effects post-ovariectomy require further investigation.

Purpose of the Study:

• To evaluate the impact of long-term norgestomet implant use in ovariectomized heifers on pregnancy maintenance and calving outcomes.
• To compare calving complications between ovariectomized heifers with norgestomet implants and control heifers.

Main Methods:

• Heifers were synchronized using norgestomet and estradiol valerate, followed by AI.
• A subset of heifers underwent ovariectomy and received subcutaneous norgestomet implants, replaced every 55 days.
• Pregnancy rates were assessed at 44 days post-AI, and calving outcomes were monitored until 273 days post-AI.

Main Results:

• Pregnancy rates at 44 days post-AI were similar between control (65%) and ovariectomized heifers with norgestomet implants (53%).
• Ovariectomized heifers with norgestomet implants experienced higher incidences of dystocia (P < 0.05), retained fetal membranes (P < 0.01), and calf mortality (P < 0.01).
• Three pregnancies were lost in ovariectomized heifers, and two heifers that lost implants became open.

Conclusions:

• Long-term norgestomet implant use in ovariectomized heifers did not significantly affect initial pregnancy rates but was associated with increased calving difficulties and calf mortality.
• The findings suggest potential adverse effects of sustained norgestomet treatment in the absence of ovaries on late-term pregnancy and parturition in cattle.