Background: Bovine brucellosis is a high-impact zoonosis that threatens both dairy productivity and public health. Despite long-standing control programs in Mexico, evidence quantifying its combined productive, reproductive, and economic effects under intensive dairy systems remains limited. Methods: Farm records from two intensively managed Holstein friesian dairies operating under fully confined housing systems in Coahuila (Mexico) were analyzed to compare brucellosis-positive (BR) and brucellosis-negative (SIN) cows across five parities (n = 32,178 lactations; 15,507 BR; and 16,671 SIN). Milk yield, days open (DOs), services per conception (SPCs), days in milk (DIMs), abortion, metritis, retained placenta (RP), and culling to abattoir were evaluated using standard linear and generalized linear models. A financial assessment estimated losses associated with unproduced milk, extra DOs, extra inseminations, abortions, hormonal protocols, feeding during extra DOs, labor, and replacement costs. Results: BR cows consistently produced less milk (−3.5 to −5.0 L·cow⁻¹·day⁻¹) and exhibited longer DOs (+10 to +34 days) and higher SPCs (+0.4 to +1.0 in four of five parities; p < 0.05). Abortion incidence was higher in BR cows (1.74–2.79%) than in SIN cows (0.69–1.59%). Estimated total economic losses reached USD 21.84 M, including unproduced milk (USD 10.20 M), extended DOs (USD 1.36 M), feed cost during extra DOs (USD 0.68 M), additional services (USD 0.21 M), hormonal protocols (USD 0.10 M), labor (USD 0.06 M), abortions (USD 0.05 M), and excess replacements (USD 0.19 M). Conclusions: Under endemic conditions, brucellosis markedly reduces dairy herd productivity and reproductive performance. Strengthened sanitary control, enhanced biosecurity, strategic culling of positive animals, and structured reproductive programs represent the most cost-effective pathway to recover milk, shorten DOs, and minimize abortions.