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

• Published in: Journal of veterinary science (Suwŏn-si, Korea) Vol. 16; no. 3; pp. 367 - 371
• Main Authors: Marques, Márcio de Oliveira, Morotti, Fábio, da Silva, Camila Bizarro, Júnior, Mario Ribeiro, da Silva, Rubens César Pinto, Baruselli, Pietro Sampaio, Seneda, Marcelo Marcondes
• Format: Journal Article
• Language: English
• Published: Korea (South) 대한수의학회 2015; The Korean Society of Veterinary Science
• Subjects: Animals; Brazil; Cattle; Estradiol - pharmacology; Estrus Synchronization; Female; Fertilization - drug effects; Insemination, Artificial - veterinary; Lactation; Original; Parity; Pregnancy; Pregnancy Rate; Progesterone - pharmacology; 수의학; Brazil; hormonal treatment; Bos indicus; fixed-time artificial insemination; resynchronization; conception rate
• ISSN: 1229-845X; 1976-555X
• DOI: 10.4142/jvs.2015.16.3.367

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%.