J Vet Sci.  2015 Sep;16(3):367-371. 10.4142/jvs.2015.16.3.367.

Influence of category-heifers, primiparous and multiparous lactating cows-in a large-scale resynchronization fixed-time artificial insemination program

• Marques MD
• Morotti F
• da Silva C
• Junior MR
• da Silva R
• Baruselli
• Seneda MM

• KMID: 2344310
• DOI: http://doi.org/10.4142/jvs.2015.16.3.367

Abstract

This study was conducted to evaluate the influence of category (heifers, primiparous or multiparous cows) on pregnancy rates in a large scale resynchronization ovulation program. Nelore heifers (n = 903), primiparous lactating cows (n = 338) and multiparous lactating cows (n = 1,223) were synchronized using a conventional protocol of estradiol/P4-based fixed-time artificial insemination (FTAI). Thirty days after ultrasonography, females who failed the first FTAI were resynchronized with the same hormonal protocol prior to a second FTAI. The pregnancy status of each cohort was evaluated by ultrasonography 30 days after each FTAI. The average conception rate after the first FTAI and resynchronization was 80.5%. Heifers had a higher conception rate (85%) than primiparous (76%) or multiparous cows (78%; p = 0.0001). The conception rate after the first FTAI was similar among heifers (57%), primiparous cows (51%) and multiparous cows (56%; p = 0.193). After the second FTAI, heifers exhibited a higher conception rate (66%) than primiparous or multiparous cows (51%; p = 0.0001). These results demonstrate the feasibility of resynchronization in large beef herds for providing consistent pregnancy rates in a short period of time. We also demonstrated that ovulation resynchronization 30 days after FTAI is particularly effective for heifers, providing a conception rate of up to 66%.

Keyword

Bos indicus; conception rate; fixed-time artificial insemination; hormonal treatment; resynchronization

MeSH Terms

Animals
Brazil
Cattle
Estradiol/*pharmacology
Estrus Synchronization
Female
Fertilization/*drug effects
Insemination, Artificial/*veterinary
Lactation
*Parity
Pregnancy
Pregnancy Rate
Progesterone/*pharmacology
Estradiol
Progesterone

Figure

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  Fig. 1 Design of hormonal treatments used for fixed-time artificial insemination (FTAI) and estrus resynchronization in Nelore heifers, primiparous and multiparous lactating cows. On Day 0, all animals received a P4 source (intravaginal device for the cows; ear implants for the heifers) in combination with 2 mg of estradiol benzoate (EB). Eight days later, the devices/implants were removed, and all females received 250 µg of cloprostenol, 300 IU of eCG, and 1 mg (cows) or 0.5 mg (heifers) of EC. FTAI was performed 48 h after the device/implant was removed. Thirty days after the first FTAI (28 to 32 days), all females were assessed by ultrasonography, and the non-pregnant bovines were resynchronized with the same hormonal treatment. The pregnancy rate was assessed by ultrasound 30 days after FTAI.

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