Leptospirosis is a common infection in domestic animals. The microscopic agglutination test (MAT) is used for serological diagnosis. From 1988 to 2007, the Leptospira Medical and Molecular Bacteriology Laboratory at the Nantes National College of Veterinary Medicine, Food Science and Engineering used the MAT to test serum samples from more than 40,000 cattle, 40,000 pigs, 20,000 horses and 9,500 dogs. Five Leptospira serogroups were prominent, with specific variations within the four animal species: Icterohaemorrhagiae, Australis, Sejroë, Grippotyphosa and Autumnalis. The prevalence and incidence of each serogroup varied for each species over the 20-year period: some serogroups were emergent during some years but disappeared later. This study reports the complex epidemiological features of leptospirosis.