Repetibilidade do diâmetro do folículo dominante e corpo lúteo dentro de ciclos estrais em bovinos de corte

Abstract

Transrectal ultrasonography has been used to study the repeatability of several ovarian characteristics, such as the number of follicles and follicular wave patterns per estrous cycle. However, there is a lack of information on the repeatability of the diameter of the preovulatory follicle as well as the diameter of the subsequent corpus luteum among consecutive estrous cycles in cattle. The aims of the present study were to investigate the repeatability of the diameter of the dominant ovulatory follicle (DOF) and corpus luteum (CL) among consecutive estrous cycles within animals. In addition, the repeatability of the maximum diameter of the dominant follicle (DF) from anovulatory and ovulatory waves and its correlation with the subsequent CL maximum diameter was evaluated. Non-lactating beef cows (n = 11; 4 years old) of Aberdeen Angus breed were used from May to December in the Northern Hemisphere. Diameters of the largest follicle and corpus luteum were measured daily by B-mode transrectal ultrasonography using a 6.5 MHz linear-array transducer (Mindray M5Vet; Nanshan, China). The same operator performed all scans. Variance components obtained from a PROC MIXED model or one-way ANOVA were used to calculate repeatability. Correlations (r) between consecutive estrous cycles and specific end points were carried out by the Spearman test and used as an indication of repeatability and association between two variables. A total of 72 estrous cycles were studied with an average of 6.5 ± 0.4 estrous cycles (range, 5–9) per animal. The number of estrous cycles with 2-, 3-, and 4-wave patterns were 54 (75%), 17 (24%) and 1 (1%), respectively. The overall repeatability (R = 0.8) and correlation (r = 0.9, p < 0.05) from Day -6 to -1 (Day 0 = ovulation) for DOF diameter among consecutive estrous cycles within animals ranged from R = 0.6 to 0.9 and r = 0.7 to 1.0, respectively. In this regard, high repeatability (R ‡ 0.7) and correlation (r ‡ 0.7, p < 0.05) were observed in 82% (9/11) and 100% (11/11) of the animals, respectively. The mean maximum diameter of the DF was greater (p < 0.0001) in ovulatory (14.4 ± 0.2 mm) compared to anovulatory (13.4 ± 0.2 mm) waves; and the repeatability among cycles for each wave was high (R = 0.6). The overall repeatability (R = 0.7) and correlation (r = 0.7, p < 0.05) for CL diameter among consecutive estrous cycles within animals ranged from R = 0.6 to 0.9 and r = 0.5 to 0.9, respectively. Moreover, 82% (9/11) and 64% (7/11) of all animals had high repeatability (R ‡ 0.7) and correlation (r = 0.7, p < 0.02) for CL diameter. The diameters of the DOF and CL from Day -6 to 5 were highly correlated (r = 0.7; p < 0.0001). The results of the present study demonstrated, for the first time, that DOF and CL diameters were highly repeatable among estrous cycles within cows, and that CL diameter was directly influenced by DOF diameter.