RESUMEN
Bovine viral diarrhea virus (BVDV) is a significant pathogen that can be shed in the semen of infected bulls. Thus, screening for BVDV in semen of bulls is recommended prior to their entry into an artificial insemination center. No previous research has compared the analytical sensitivity of reverse transcription-nested polymerase chain reaction (RT-nPCR) and virus isolation assays for detection of BVDV in semen from an infected bull. Therefore, the goals of this research were to compare the analytical sensitivity of RT-nPCR and virus isolation assays for BVDV in semen and to apply these assays to determine the prevalence in the Southeastern United States of bulls that lack viremia yet shed BVDV in semen. Semen collected from a bull that was persistently infected with BVDV was serially diluted (1/10) in semen from uninfected bulls and frozen in liquid nitrogen as raw, partially extended or fully extended semen. Subsequently, samples of semen were assayed by virus isolation and RT-nPCR. Viral detection was more sensitive in extended semen samples than in raw semen samples and more sensitive by RT-nPCR than virus isolation. After this evaluation of analytical sensitivity, serum and semen were collected from 558 post-pubertal bulls in our region. These samples were tested for BVDV by virus isolation. Partially extended semen was also assayed for BVDV by RT-nPCR. All samples were negative by all assays for BVDV. The application of analytically sensitive assays reveals a very low prevalence (
Asunto(s)
Diarrea Mucosa Bovina Viral/diagnóstico , Virus de la Diarrea Viral Bovina/aislamiento & purificación , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa/veterinaria , Semen/virología , Animales , Diarrea Mucosa Bovina Viral/epidemiología , Bovinos , Virus de la Diarrea Viral Bovina/genética , Masculino , Prevalencia , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa/métodos , Sensibilidad y Especificidad , Sudeste de Estados Unidos/epidemiologíaRESUMEN
An artificial insemination dose for mares consisting of 500 million progressively motile spermatozoa is considered "standard" by most clinicians. However, little information is available directly comparing pregnancy outcome among methods of evaluating and selecting spermatozoa for insemination. The objective of this study was to determine if the method of spermatozoal evaluation and selection influences fertility as measured by pregnancy outcome. Mares were inseminated with 100 or 500 million spermatozoa that were selected for progressive motility, normal morphology, hypoosmotic swelling or absolute number regardless for evaluation method or quality. Thirty-two breeding cycles were tested for each treatment group and at each spermatozoal dose. Pregnancy outcomes were 44 and 41%, 55 and 41%, 39 and 31%, and 45 and 41%, for the 100 and 500 million progressively motile, morphologically normal, hypoosmotic swelling positive and absolute number treatment groups, respectively. Pregnancy outcome did not differ among methods of spermatozoal evaluation and selection for artificial insemination in the 100 (P=0.52) or 500 (P=0.78) million spermatozoa groups. Also the total number of spermatozoa and the absolute number of progressively motile, morphologically normal or hypoosmotic swelling positive spermatozoa inseminated, were not closely associated with pregnancy outcome in the 100 (P=0.24, 0.29, 0.33 and 0.38, respectively) or 500 (P=0.20, 0.84, 0.50 and 0.74, respectively) million spermatozoa groups. In this study, we found that the method of spermatozoal evaluation did not offer an advantage for pregnancy when used to select spermatozoa for insemination at the doses tested. These results were surprising, as we expected there would be differences among the evaluation methods. Instead, we found that evaluating spermatozoa offered no advantage for pregnancy over simply inseminating with a specified number of spermatozoa not selected for any particular characteristic under the conditions of our experiment.