Reproductive adaptation of local Algerian ewes to seasonal constraints: follicular dynamics and oocyte morphology during anestrus

Seasonal anestrus in ewes is typically associated with reduced ovarian activity due to photoperiod-driven reduction of gonadotropin secretion. However, locally adapted sheep breeds raised under subtropical conditions may exhibit adaptive reproductive mechanisms that mitigate this seasonal constraint. This study is the first in Algeria to evaluate follicular dynamics, oocyte yield, and oocyte morphology in local ewes during the anestrous period. A total of 124 ovaries were collected from abattoir-derived ewes between March and June. Visible follicles were classified as small (≤ 2 mm) or large (≥ 3 mm), and recovered oocytes were morphologically graded (Q1–Q4). Overall, 1,284 follicles and 430 oocytes were obtained. Ovarian examination revealed a predominance of small antral follicles (median 32 [16–89] vs. 11 [5–25]; p  < 0.01), with no significant difference in total follicle numbers between right and left ovaries (median 23 [11–53] vs. 20 [13–47]; p  ≥ 0.05). In contrast, a significant right-sided asymmetry was observed in oocyte recovery (median 12 [10–18] vs. 10 [6.5–13]; p  = 0.04), particularly for high-grade oocytes (Q1 + Q2) (median 7 [4–8] vs. 3 [1.5–6.5]; p  = 0.02). Moreover, higher high-grade oocyte-to-follicle ratios were observed at the ovarian level in ovaries characterized by a greater proportion of large follicles, particularly in the right ovary (1.52 ± 0.29 vs. 0.42 ± 0.07; p  < 0.001). These findings demonstrate that local Algerian ewes maintain active follicular development and produce high morphological grade oocytes during seasonal anestrus, reflecting adaptive reproductive flexibility under subtropical environmental conditions. This resilience supports the potential year-round application of assisted reproductive technologies in locally adapted sheep production systems.