PARENT SESSION

(W711) REPEATABILITY OF 2- AND 3-WAVE PATTERNS DURING THE BOVINE ESTROUS CYCLE.

Jaiswal, Rajesh¹, Singh, Jaswant¹, Marshall, Laura¹, Adams, Gregg¹, ¹ University of Saskatchewan, Saskatoon, SK, Canada

ABSTRACT- Cattle exhibit 2 or 3 waves (W) of follicular development during an interovulatory interval (IOI). Our objectives were to determine if a given IOI pattern is repeatable within individuals and to characterize factors associated with an IOI pattern. A retrospective analysis was performed of ultrasonographically derived follicular data from 91 complete IOI of 31 heifers. Data were centralized to the day of emergence of wave 1. A subset comprising 75 IOI from 15 heifers, where data for more than one IOI per heifer was available, was used for evaluating repeatability. Frequencies of non-alternating and alternating IOI patterns were determined. Data were analyzed by chi-square and t-tests. Average lengths (mean and 95% confidence interval) of 2W- and 3W-IOI were 19.9±0.4 and 22.6±0.5 days, respectively, (P<0.01). The majority of IOI ≤21 days were of the 2W pattern (52/61, 85%), whereas, only 26% (8/31) were of the 3W pattern. Conversely, the majority of IOI ≥22 days were of the 3W pattern (23/31, 74%), whereas, only 15% (9/61) were of the 2W pattern. Five of 15 heifers (33%) exhibited exclusively 2W pattern for 5 to 6 consecutive IOI. The proportion of non-alternating patterns was greater than the proportion of alternating patterns (42/60 vs. 18/60; P<0.01). The first significant decrease in diameter of the wave 1 dominant follicle occurred later in 2W- versus 3W-IOI (14.0±0.31 vs. 10.68±0.46; P<0.01). Consequently, the day when the largest follicle of wave 2 became dominant was delayed in 2W- versus 3W-IOI (14.9±0.2 vs. 12.8±0.4; P<0.01). There was an earlier onset of regression of the corpus luteum in 2W- versus 3W-IOI (14.0±0.2 vs. 16.6±0.4; P<0.01). A larger number of 4 to 5 mm follicles emerged per IOI during 3W-versus 2W-IOI (48.4±3.2 vs. 34.9±2.0; P<0.01). The duration of an IOI is predictive of the wave pattern within IOI. A pattern (2- or 3-wave) is repeatable within individuals. The first dominant follicle of 2W-IOI has a longer period of dominance than its 3W counterpart; hence, factors that influence the first dominant follicle may be responsible for regulating the IOI pattern. There is a higher attrition of follicles in 3W-IOI; hence, depletion of the follicular reserve and onset of the reproductive senescence may occur earlier in individuals exhibiting predominantly 3W- compared to 2W-IOI patterns.

KEY WORDS: cattle, repeatability, interovulatory interval, wave pattern