J Vet Sci.  2014 Sep;15(3):433-437. 10.4142/jvs.2014.15.3.433.

Effects of progestagen exposure duration on estrus synchronization and conception rates of crossbreed ewes undergoing fixed time artificial insemination

• Blaschi W
• Lunardelli PA
• Marinho LS
• Max MC
• Santos GM
• Silva-Santos KC
• Melo-Sterza FA
• Baldassarre H
• Rigo TR
• Seneda MM

• KMID: 2155628
• DOI: http://doi.org/10.4142/jvs.2014.15.3.433

Abstract

Synchronization of estrus and ovulation are of paramount importance in modern livestock improvement programs. These methods are critical for assisted reproduction technologies, including artificial insemination and embryo transfer, that can increase productivity. In the current study, subcutaneous implants containing norgestomet were placed for long (14 days), medium (9 days), and short (5 days) periods of time in 70 crossbred ewes undergoing fixed-time artificial insemination. The resulting effects on estrus synchronization and conception rates were subsequently evaluated. Among the synchronized ewes, 85.7% (60/70) underwent estrus over a period of 72 h after progestagen treatment ceased. The shortest mean interval between withdrawal of the device and onset of estrus (34.2 +/- 8.9 h) was observed in the G14 days of P4 group (p < 0.05). The conception rate of the G14 days of P4 group was statistically higher than that of the other groups (83.3% vs. 60.9% vs. 47.8%; p < 0.05). In conclusion, 14 days of norgestomet treatment produced higher conception rates and a greater number of pregnancies at the beginning of the breeding season.

Keyword

estrus synchronization; norgestomet; ovine; pregnancy; progesterone

MeSH Terms

Animals
Drug Implants/therapeutic use
Estrus Synchronization/drug effects/*methods
Female
Fertilization/drug effects
Insemination, Artificial/methods/*veterinary
Pregnenediones/administration & dosage/*pharmacology
Sheep
Drug Implants
Pregnenediones

Figure

• 

  Fig. 1 Schematic representation of the fixed-time artificial insemination (FTAI) protocols used for crossbred sheep in Brazil. For G 14 days of P4 , the progestagen device (1.5 mg norgestomet, 1/2 Crestar) was implanted in the ear on the morning of day 0 (a random day of the estrous cycle) and remained in place until day 14 when 22.5 µg D-cloprostenol (Preloban) and 400 IU equine chorionic gonadotropin (eCG; Folligon) were administered. For Group 9 (G9 days of P4), the progestagen device remained in place until day 9 when sodic cloprostenol and eCG were administered at the same doses as in G14 days of P4. For G5 days of P4, the progestagen device remained in place until day 5 when sodic cloprostenol and equine chorionic gonadotropin were administered at the same doses as in G14 days of P4.

• 

  Fig. 2 Number of ewes coming in estrus during the 72-h observation period after synchronization with the norgestomet implant for 14, 9, or 5 days.

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  Fig. 3 Conception rates for ewes synchronized by hormonal protocols using norgestomet implants for 14, 9, or 5 days. Different letters over the columns indicate significant differences (p < 0.05).

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