AVALIAÇÃO DA PERFORMANCE DE RECEPTORAS MEIO SANGUE ANGUS-NELORE PELAS CARACTERÍSTICAS LUTEAIS

Abstract

The performance of a recipient is determined mainly by conception and pregnancy rates. Pregnancy is maintained mainly by the action of the hormone progesterone, which is released by the corpus luteum. The corpus luteum (CL) is a structure formed after ovulation from luteinized follicular cells. The early formation of the corpus luteum and high progesterone production of Angus females arouse interest in their role as recipients of embryos for beef cattle, as is the case on a large scale with Nellore females in Brazil. Combining the rusticity of the Nellore breed with the luteal function of the Angus breed would be interesting to generate more efficient embryo recipients. In this context, the present study aimed to evaluate the performance of Angus-Nellore females as embryo recipients through their luteal characteristics and conception rates. Data from 59 recipient bovines of reproductive age, of Angus-Nellore crossbred, submitted to a hormonal protocol for estrous cycle synchronization were analyzed. The recipients were evaluated for the presence, laterality and degree of the corpus luteum, and the conception rates were confirmed by transrectal ultrasonography at 30 and 55 days of gestation. Statistical analysis was performed by logistic regression, using the SAS program, at 5% significance. The rate of recipients with the presence of corpus luteum after hormonal protocol for estrous synchronization in this study was 94.11% in 2022 and 86.30% in 2023. These rates demonstrate an excellent response of Angus-Nellore recipients to hormonal treatment. The results demonstrated conception rates of 50.00% at 30 and 55 days of gestation for recipients with corpus luteum on the right side and 44.44% on the left side. Regarding the CL grade, the conception rates were 47.82% for grades 1 and 2 and 47.05% for grade 3. There was no significant difference for laterality and grade of the corpus luteum (P > 0.05). The present study revealed a good potential for using Angus-Nellore female cattle as embryo recipients. The conception rate is an important indicator of luteal functionality. Even though the grades (1, 2 or 3) and laterality of the corpus luteum (right or left) did not demonstrate a significant impact in this study, it still suggests the aptitude of these recipients for high progesterone production and high potential for maintaining pregnancy, reflected by the good conception rates. Furthermore, the pregnancy rates observed at 30 and 55 days of gestation reinforce that multiple factors are involved in successful conception, such as nutritional status, adequate management and careful selection of recipients. It is concluded that the half-blood Angus-Nellore female cattle evaluated in this study showed excellent performance as embryo recipients. The conception rates observed were promising and were not affected by variations in the luteal characteristics of laterality (right or left) and degree of the corpus luteum (1, 2 or 3).