Blood Protozoan Infection Disrupts Ovarian Follicular Development in Dairy Cattle: A Mechanistic Link to Reproductive...

Haemoprotozoan infections are a pervasive threat to livestock health in tropical regions, yet their specific impacts on reproductive function remain unidentified.

This study tested the hypothesis that blood protozoan infection induces anaemia and disrupts ovarian follicular dynamics, thereby contributing to infertility.

Forty cows (n = 40) with reproductive complaints were examined, and blood samples were analysed for protozoan infection and haemoglobin (Hb) concentration. Ten cyclic cows without any reproductive problems were served as controls. Ex vivo assessments were performed on reproductive tracts (n = 30) collected from an abattoir, followed by histopathological examination of ovarian tissues. A complementary rabbit (n = 10) model was conducted to assess haematological and iron metabolic changes across the oestrous cycle.

Among 30 symptomatic cows, 100% tested positive for blood protozoan infection, with distribution rates of 53.3% (8/15) in anoestrus, 40.0% (4/10) in repeat breeding and 20.0% (1/5) in conception failure. Infected cows exhibited significantly lower Hb levels (6.6 g%) compared to non-infected controls (10.6 g%). Cows with Hb ≤6.5 g% exhibited rudimentary ovaries, small to medium follicles and follicular cysts, whereas those with Hb ≥7 g% showed normal ovarian morphology. Histopathology confirmed cystic degeneration, fibrosis and aberrant follicular structures in infected cows. The rabbit model showed a significant decline in Hb and disruptions in serum iron levels during the anoestrus phase, reinforcing the link between iron metabolism and reproductive cyclicity.

Our findings demonstrate that subclinical blood protozoan infection severely impairs ovarian health through anaemia-induced hypoxia and metabolic disturbances, establishing a direct link to infertility.