Histological study of the canine ovarian suspensory ligament and its implications for neutering procedures

BACKGROUND: The ovarian suspensory ligament (OSL) is routinely manipulated during ovariectomy/ovariohysterectomy in dogs. Despite its surgical relevance, it is traditionally described only macroscopically as a fibrous band, and its microscopic composition has not been characterized. OBJECTIVE: To provide the first detailed histological and ultrastructural characterization of the canine ovarian suspensory ligament. METHODS: OSL samples were collected from twenty female dogs and processed for histology. Sections were stained with Masson's trichrome, Sirius Red, Weigert's resorcin-fuchsin, and anti-α-smooth muscle actin immunohistochemistry. Tissue components were quantified by surface density using a point-counting method. Scanning electron microscopy was performed to assess ultrastructural organization. Comparisons were made between sides and across age, body weight, and reproductive variables (p < 0.05). RESULTS: The OSL did not resemble a dense collagenous ligament. Instead, it showed a heterogeneous architecture dominated by smooth muscle (46.3 ± 11.7%), followed by collagenous connective tissue (32.9 ± 8.9%), elastic system fibers (5.3 ± 2.1%), adipose tissue (2.7 ± 2.9%), and blood vessels (2.1 ± 2.7%). Immunohistochemistry confirmed the smooth muscle phenotype, and scanning electron microscopy demonstrated a loosely organized collagen network. No significant differences in composition were observed according to side, age, body weight, estrous history, or parity. CONCLUSIONS: The canine OSL is not a classical dense fibrous ligament but a muscular ligament. These findings refine its anatomical characterization and have implications for surgical technique and future studies on pharmacologic relaxation.