A cross-sectional serological survey was carried on from September 2017 to December 2020. Using a probabilistic two-stage sampling, 25 farms and fifteen animals per farm were selected. SENASA (Servicio Nacional de Sanidad y Calidad Agroalimentaria) and Fundación Aftosa provided the region's database. In the first stage, the number of farms to be selected was calculated using the ProMesa 1.3 programme (12 ) using the following formula:
Where p is the expected seroprevalence of cows reactive to Leptospira, z is the confidence level, ROH is the homogeneity rate, b is the number of animals selected per farm and e is the acceptable (allowable) absolute error. Our assumptions were as follows: a prevalence of 20.33% (13 ), a relative error of 33%, a low homogeneity rate (0.06–0.12) (14 (link)) and 15 animals sampled per farm. The minimum sample size estimated was 25 farms (375 animals). More farms were included from Ayacucho (14) because this department has the largest number of cattle farms. The second stage was conducted on each farm through systematic randomization of the animals. The animals included in the study were bulls and breeding females ≥15 months of age, that were not vaccinated against Leptospira spp. or had been vaccinated more than 6 months before sampling. In addition, a questionnaire was administered to collect epidemiological information about the potential risk factors associated with seropositivity to Leptospira spp. The survey was based on general production and environmental characteristics, feeding practices, health and reproduction status. All farms were georeferenced using Global Positioning Systems (GPS) to perform spatial analysis and subsequent search for meteorological and satellite information such as the presence of water bodies, potential evapotranspiration, temperature and solar radiation. Water bodies were detected using information from the Landsat 8 satellite (spatial resolution of 30 meters) and calculated with MNDWI (Modified Normalized Difference Water Index) (15 (link)) with the QGIS software. The potential evapotranspiration was obtained through the EOS-Terra satellite and estimated using the ENVI software. The temperature was calculated monthly through data from the National Meteorological Service and solar radiation, using information from the sensor CERES (Clouds and the Earth's Radiant Energy System) (16 (link)). On the farms, blood samples were collected from the animals by venipuncture. The blood was allowed to clot at room temperature and centrifuged at 1,500 rpm for 15 min. The sera were separated and stored at −20°C.
Where p is the expected seroprevalence of cows reactive to Leptospira, z is the confidence level, ROH is the homogeneity rate, b is the number of animals selected per farm and e is the acceptable (allowable) absolute error. Our assumptions were as follows: a prevalence of 20.33% (13 ), a relative error of 33%, a low homogeneity rate (0.06–0.12) (14 (link)) and 15 animals sampled per farm. The minimum sample size estimated was 25 farms (375 animals). More farms were included from Ayacucho (14) because this department has the largest number of cattle farms. The second stage was conducted on each farm through systematic randomization of the animals. The animals included in the study were bulls and breeding females ≥15 months of age, that were not vaccinated against Leptospira spp. or had been vaccinated more than 6 months before sampling. In addition, a questionnaire was administered to collect epidemiological information about the potential risk factors associated with seropositivity to Leptospira spp. The survey was based on general production and environmental characteristics, feeding practices, health and reproduction status. All farms were georeferenced using Global Positioning Systems (GPS) to perform spatial analysis and subsequent search for meteorological and satellite information such as the presence of water bodies, potential evapotranspiration, temperature and solar radiation. Water bodies were detected using information from the Landsat 8 satellite (spatial resolution of 30 meters) and calculated with MNDWI (Modified Normalized Difference Water Index) (15 (link)) with the QGIS software. The potential evapotranspiration was obtained through the EOS-Terra satellite and estimated using the ENVI software. The temperature was calculated monthly through data from the National Meteorological Service and solar radiation, using information from the sensor CERES (Clouds and the Earth's Radiant Energy System) (16 (link)). On the farms, blood samples were collected from the animals by venipuncture. The blood was allowed to clot at room temperature and centrifuged at 1,500 rpm for 15 min. The sera were separated and stored at −20°C.
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