Pregnancy rates during experimentation in dairy cows

Area of Science:

• Veterinary Science
• Reproductive Biology
• Animal Science

Background:

• Artificial insemination (AI) protocols in dairy cows are crucial for reproductive efficiency.
• Hormonal monitoring is essential for understanding factors affecting pregnancy rates.
• Experimental stress can negatively impact animal physiology and reproductive outcomes.

Purpose of the Study:

• To investigate the impact of different AI and blood sampling protocols on pregnancy rates in dairy cows.
• To determine the role of hormonal status, specifically progesterone and estradiol, in early embryonic mortality.
• To assess the effect of acclimatization and experimental stress on ovulation timing and conception.

Main Methods:

• Dairy cows underwent artificial insemination with blood sampling via jugular venepuncture or cannulae.
• Hormonal status (progesterone, estradiol) was monitored throughout the estrous cycle.
• Pregnancy rates were assessed on day 16 post-insemination.
• Cows were either subjected to immediate experimentation or acclimatized to the facility prior to the protocol.

Main Results:

• Single AI with jugular venepuncture yielded a 27.8% pregnancy rate.
• Double AI with jugular cannulae did not improve pregnancy rates (27.3%).
• Acclimatization significantly increased pregnancy rates to 85.7% (P < 0.005).
• Acclimatized cows showed earlier ovulation (advanced estradiol decline) without altered progesterone levels.
• Non-pregnant cows exhibited delayed estradiol decline and lower progesterone.

Conclusions:

• Acclimatization is a critical factor for improving dairy cow pregnancy rates under experimental conditions.
• Impaired ovulation, suggested by delayed estradiol decline, is a primary cause of pregnancy failure in stressed cows.
• While inadequate progesterone may contribute to early embryo loss, ovulation timing is a more significant determinant of success in this context.