Repeatability of 2-wave and 3-wave patterns of ovarian follicular development during the bovine estrous cycle

Abstract

Characteristics predictive of a 2-wave versus 3-wave pattern of ovarian follicular development during the interovulatory interval (IOI) were examined by ultrasonographic monitoring of 91 IOIs from 31 beef heifers. Repeatability of the wave pattern within individuals and the effects of season and age were determined using a subset of 75 IOIs from 15 heifers examined for multiple IOIs. The 2-wave pattern was detected in 62 of 91 (68%) IOIs, and the 3-wave pattern was detected in 29 of 91 (32%) IOIs. The preponderance of the 2-wave versus 3-wave pattern (P < 0.05) was not influenced by season (P = 0.61) but was even greater in the more mature age group (P = 0.02). The majority of IOIs ≤21 d was of the 2-wave pattern (88%; P < 0.05), whereas the majority of IOIs ≥22 d was of the 3-wave pattern (78%; P < 0.05). The proportion of nonalternating patterns (repeatability) was more than twofold greater than the proportion of alternating patterns (70% vs. 30%; P < 0.01). This relationship was consistent among seasons (P < 0.01) and even more marked in the more mature age group (P = 0.01). Emergence and follicular dominance of Wave 2 were delayed (P < 0.01), and the onset of corpus luteum regression was earlier (P < 0.01) in 2-wave versus 3-wave IOI. In conclusion, the duration of the IOI was predictive of the wave pattern, and the pattern was repeatable within individuals. Factors influencing the period of follicular dominance of Wave 1 in 2-wave versus 3-wave IOI may be responsible for regulating the wave pattern and may be associated with heifer maturity or relative nutritional demand during the postpubertal period. The impact of greater follicular attrition recorded in 3-wave versus 2-wave IOI on ovarian depletion and reproductive senescence is worthy of critical evaluation.