title: Influence of category--heifers, primiparous and multiparous lactating cows--in a large-scale resynchronization fixed-time artificial insemination program.
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%.
authors: Geraembryo, Cornélio Procópio 86300-000, Brazil.
authors: Márcio de Oliveira
authors: Mde O
authors: Marques
authors: Fábio
authors: F
authors: Morotti
authors: Camila Bizarro
authors: CB
authors: da Silva
authors: Mario Ribeiro
authors: MR
authors: Júnior
authors: Rubens César Pinto
authors: RC
authors: da Silva
authors: Pietro Sampaio
authors: PS
authors: Baruselli
authors: Marcelo Marcondes
authors: MM
authors: Seneda
mesh_terms: D000818:Animals; D001938:Brazil; D002417:Cattle; D004958:Estradiol / Q000494:pharmacology*; D004973:Estrus Synchronization; D005260:Female; D005306:Fertilization / Q000187:drug effects*; D007315:Insemination, Artificial / Q000662:veterinary*; D007774:Lactation; D010298:Parity; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000494:pharmacology*
chemical_list: D011374:Progesterone; D004958:Estradiol
keywords: Bos indicus; conception rate; fixed-time artificial insemination; hormonal treatment; resynchronization