Seroconversion to bovine viral diarrhoea virus and infectious bovine rhinotracheitis virus in dairy herds of Michoacan, Mexico José C. Segura-Correa & José L. Solorio-Rivera & Laura G. Sánchez-Gil Accepted: 31 July 2009 / Published online: 15 August 2009 # Springer Science + Business Media B.V. 2009 Abstract Bovine viral diarrhoea virus (BVDV) and infectious bovine rhinotracheitis virus (IBRV) are important viral diseases around the world. The objective of this study was to estimate the incidence of seroconversion to BVDV and IBRV and to identify associated risk factors in dairy herds of Michoacan, Mexico. The longitudinal study included 62 herds and ran from December 2001 to November 2002. The total number of animals enrolled and completing the study were 392 and 342 animals for BVDV and 925 and 899 animals for IBRV. Animals were tested monthly for 12 months, for the presence of anti- bodies. Risk factors were: herd size (2–9, 10–25 and 26–55 animals), herd serostatus (seropositive or seronegative, only for IBRV), age group of the animal (6 to 12, 13 to 24, 25 to 48 and > 48 months) and animal origin (born in farm, purchased). The cumu- lative incidences for BVDV and IBRV were 16.4% and 3.4%, respectively; whereas, the incidence densi- ty rates for BVDV and IBRV were 15.9 and 2.9 per 1000 animal-months at risk, respectively. Seroconver- sion curves were statistically different for age group for BVDV and IBRV and for herd status for IBR. The relatively high incidence of seroconversion for BVDV suggests that a successful control programme should be oriented towards the identification and elimination of the PI animals and towards avoiding the introduc- tion of PI cattle to the farm. The scenario of IBRV is favourable to implement a programme directed to reduce the number of new seropositive herds. Keywords Bovine viral diarrhoea virus . Infectious bovine rhinotracheitis virus . Incidence . Risk factors . Tropics . Mexico Introduction In Mexico, the diseases that cause abortions in cattle produce economical losses of about $937 to $1100 per aborted cow (Córdova et al. 2003). Abortions have been associated with bacterial, viral or fungal infections. Bovine viral diarrhoea and infectious bovine rhinotracheitis are among the viral diseases present in Mexico. These diseases may cause embry- onic death, mummification, abortion, infertility and dead or weak calves that die within the first days of life (Fray et al. 2000). These viruses are also implicated in the bovine respiratory disease complex, which is considered one of the major causes of economic losses in the cattle industry (Houe 2003, Muylkens et al. 2007). A previous seroprevalence Trop Anim Health Prod (2010) 42:233–238 DOI 10.1007/s11250-009-9411-y J. C. Segura-Correa (*) Facultad de Medicina Veterinaria y Zootecnia, UADY, Km. 15.5 carretera Mérida-Xmatkuil, A.P.4-116, Itzimná, Mérida, Yucatán, México e-mail: segura52@hotmail.com J. L. Solorio-Rivera : L. G. Sánchez-Gil Facultad de Medicina Veterinaria y Zootecnia, Universidad Michoacana de San Nicolás de Hidalgo, Morelia, Michoacán, México