CLINICAL MANIFESTATIONS AND REPRODUCTIVE IMPACTS

Delayed ovulation in cattle is a reproductive disorder characterized by delayed release of oocytes from preovulatory follicles, resulting in a variety of clinical manifestations at the individual and herd level [116]. A hallmark clinical sign is follicular persistence, in which the dominant follicle remains in the ovary without ovulation despite reaching physiological size [117]. Ultrasonography typically shows a large, unruptured follicle, sometimes with partial luteinization of the follicle wall [118]. This follicular persistence leads to asynchronous follicular waves and disrupts normal hormonal patterns [27]. Clinically, a practical diagnostic approach combines sequential estrus monitoring, ovarian ultrasonography to identify persistent follicles, and evaluation of metabolic or inflammatory risk factors to guide targeted hormonal or management interventions.

Figure 3: Multifactorial risk factors contributing to delayed ovulation in cattle. The figure was prepared by the authors based on information synthesized from previous studies [2, 91, 101, 102, 103, 104, 105, 106, 107, 108, 109, 110, 111, 112, 113, 114, 115]. The graphical illustration was generated with the assistance of ChatGPT (OpenAI, San Francisco, CA, USA) and designed using Canva (Canva Pty Ltd., Sydney, Australia). The final figure was critically reviewed, refined, and validated by the authors to ensure scientific accuracy and consistency with the cited literature.

Delayed ovulation also affects estrus behavior [119]. Cows may show prolonged, irregular, or weak estrus (silent heat) [120], caused by an imbalance of estradiol and progesterone due to impaired follicle dynamics and CL formation [11]. Weak estrus expression reduces the accuracy of estrus detection in the field, contributing to mistimed insemination [45].

At the reproductive level, delayed ovulation decreases conception rates [3]. The condition causes a mismatch between available healthy oocytes and optimally capacitated sperm [121], reducing fertilization success and increasing early embryonic loss [122]. It often results in repeat breeder status, defined as failure to conceive after three or more consecutive inseminations in the absence of anatomical or infectious reproductive disorders. This increases reproductive costs, including additional inseminations, labor, and reduced milk or meat production [123].

Long-term consequences include prolonged calving intervals—the time between successive births [10]. At the herd level, these effects differ by production system: in dairy herds, prolonged calving intervals reduce annual milk yield, increase days open, and raise replacement rates; in beef herds, consequences include lower calf crop percentages, delayed weaning weights, and slower herd turnover [124]. Chronic ovarian dysfunction may also lead to luteal insufficiency, disrupting subsequent estrus cycles and reducing overall herd reproductive efficiency [19].