Estratégias hormonais após inseminação artificial em tempo fixo em fêmeas nelore

Abstract

Early embryonic mortality represents a significant economic loss due to repeated estrus and increases the costs of artificial insemination, resulting in a longer interval between calvings and an exponential reduction in the farm's net production. Considering the improvement of embryonic survival rates, some post-ovulatory strategies have been proposed with the aim of increasing the capacity of progesterone production by the corpus luteum during maternal recognition of pregnancy. Thus, this study was conducted to evaluate the effects of the administration of equine chorionic gonadotropin, gonadotropin-releasing hormone, and the intravaginal progesterone device, five days after fixed-time artificial insemination, on the conception rate and luteal development of Nellore cows. Multiparous, primiparous and nulliparous Nellore females with body condition score between 2.5 and 3 (on a scale of 1 to 5) were randomly distributed into 4 experimental groups involving application of 200 IU of eCG, 25 μg of GnRH, insertion of the first use intravaginal device (1g) and control group, on the fifth day after FTAI (D15). Control females were subjected to the same management without the application of drugs. The size of the corpus luteum on D15 and D22, the pregnancy rate of the groups (D40), and analysis of costs of the protocols were evaluated. Statistical analyses were performed at the 5% probability level using SAS software, copyright © 2012-2020, SAS Institute Inc., Cary, NC, USA. Progesterone supplementation after IATF through the use of a first-use intravaginal progesterone device, eCG or GnRH did not promote the formation of accessory corpora lutea or increase the pregnancy rate in Nellore females with ECC between 2.5 and 3 in the conditions of Northern Minas Gerais.