Distribution, Morphometric Evaluation and Steroidogenic Profile of Ovarian Follicles in Cyclic and Acyclic Buffalo (Bubalus bubalis)

Abstract

The water buffalo (Bubalus bubalis) is an economically important livestock species in tropical and subtropical regions, contributing substantially to milk, meat, and hide production. However, poor reproductive efficiency remains a major constraint, with acyclicity representing one of the most prevalent disorders affecting fertility and productivity. Acyclicity commonly occurs during the postpartum period or under conditions of nutritional, environmental, or metabolic stress, ultimately increasing the number of days open, veterinary interventions, and culling rates. Understanding the distribution pattern of follicles and their functional status is therefore essential for developing targeted reproductive interventions. In this study, paired ovaries were collected from healthy adult buffaloes (n=75) at slaughter. Ovaries were classified as cyclic or acyclic based on the presence of a CL. Surface follicles were enumerated and categorized into small (<5 mm), medium (5–10 mm), and large (>10 mm). Follicular fluid from large follicles was aspirated for estimation of estradiol (E₂), progesterone (P₄), androstenedione (A₄), and testosterone (T), and follicles were retrospectively classified as active (P₄:E₂ <1), intermediate (P₄:E₂ 1–10), or atretic (P₄:E₂ >10). Acyclic buffaloes exhibited a greater proportion of ovaries with only small follicles (36.36%), compared with cyclic animals (9.43%), whereas only large follicles (>10 mm) occurred predominantly in cyclic buffaloes (26.42% vs. 4.55%). Cyclic buffalo ovaries also showed stage-dependent shifts in follicle distribution, with only large follicles observed in 26.1% at Stage 3 and 57.1% at Stage 4. Despite these morphological differences, large follicles from cyclic and acyclic buffaloes displayed comparable steroidogenic patterns, with progressive increases in P₄ and decreases in E₂ from active to atretic categories. Further, the E₂:A₄ ratio was also significantly greater in the active follicle than in the atretic follicle. Thus, evaluation of the follicles based on their steroidogenic profile provided biologically meaningful insights into follicular atresia, which is more informative than classification based solely on size and stages of cyclicity. This approach would be useful for developing hormonal interventions to induce cyclicity and augment reproductive efficiency in buffaloes.