6th International Symposium on Stallion Reproduction Systematic and regular vaccination against rhinopneumonitis of all horses in a breeding stud can decrease the risk of excretion of EHV1 in semen of healthy stallions O. Alkhleif , J.-L. Pellerin , M. Larrat , C. Roux , E. Maindron , L. Richard , F. Fieni , and J.-F. Bruyas 1 1 LUNAM University, Oniris, (Nantes-Atlantic National College of Veterinary Medicine, Food Science and Engineering), Department of Research into the Sanitary Security of Reproduction Biotechnologies UPSP 5301 DGER, France, 2 IFCE (French National Studs), Le Lion d'Angers, France, 3 IFCE (French National Studs), La Roche sur Yon, France In a previous study [1], EHV1 DNA was identified in semen from 51 of 390 healthy breeding stallions (13%) in different studs in 2004 and 2005. In two of these studs, EHV1 DNA was detected in 50% (10/20) and 55% (16/29) samples, respectively. The aims of the present study (conducted in 2011) were to identify in those two studs stallions shedding virus in semen. In the previous investigation of the two studs, only very few stallions (2/20 and 13/29) had been vaccinated against rhinopneumonitis and 7 of them gave semen samples positive for EHV1DNA. Since the time of this previous study, all stallions in both studs had been vaccinated against EHV1 on a regular basis. Semenwas collected once at the start of the breeding season from 20 and 15 stallions in the two stud farms and immediately frozen at -20 C until analysis by PCR. In April and May, semen of five stallions from each stud was iteratively collected 5 times 7-14days apart and immediately frozenuntil testing byPCR. The EHV1 DNA was detected neither in the individual samples of 35 stallions nor in the 5 samples collected repeatedly from 10 stallions. Between the previous and the present study, neither housing normanagement of stallions in the two studs nor breeding activities had changed. Only one stallion in each stud recognized in 2004 to excrete the virus in semen was still at stud and tested again in the present study. All other stallions arrived in the studs between 2006 and 2010. For the previous study, semenwas collected late in the breeding season, whereas in this study, semen collections were performed at the end of the period of sexual rest, and during the first two months of the breeding season. Vaccination against herpes virus does not 0737-0806/$ see front matter 2012 Elsevier Inc. All rights reserved. prevent contamination or latent carriage, or even the emergence of clinical signs, but when an entire herd is vaccinated, virus circulation between animals is significantly reduced. Thus, regular vaccination of an entire herd for several years appears to reduce the risk of EHV1 shedding in semen. While in the two studs over 50% of stallions were shedding EHV1 virus in semen in 2004, no virus was detected in any stallion in 2011, i.e. after introduction of routine vaccination.