Abstract. Boar studs are continuously monitored for the presence of porcine reproductive and respiratory syndrome virus (PRRSV) by testing different biological samples by reverse-transcription polymerase chain reaction (RT-PCR). In most cases, samples are run in pools, even though the impact of pooling on the sensitivity of RT-PCR is unknown. The objective of this study was to evaluate the feasibility of using PCR on pooled samples through the estimation of the sensitivity of RT-PCR on different biological samples run individually, in pools of 3 and in pools of 5. Twenty-nine boars were inoculated with a low virulent PRRSV isolate. Serum, blood swab, and semen samples were obtained from each boar every 2 to 3 days for 2 weeks. Each sample was tested by RT-PCR undiluted or diluted 1:3 and 1:5 with negative samples. Eleven of the 29 boars did not appear to get infected from the inoculum, as evidenced by no seroconversion 15 days after inoculation. Data from the other 18 boars showed that serum was the best sample to detect PRRSV during acute infection, with the blood swab sample performing almost as well. Semen samples failed to detect PRRSV infection in most of the cases. Pooling samples at pool sizes of 3 and 5 resulted in a decrease in the sensitivity of RT-PCR. Sensitivity was reduced by 6% and 8%, respectively, when serum or blood swab samples were run in pools of 5. The impact of pooling on the sensitivity of PCR was higher in samples taken during the beginning of the viremic period.
The objective of this experiment was to determine the reproductive performance and factors that affect on-farm application of low-dose intrauterine insemination (IUI) in sows. Four hundred twenty-two sows were used in a simple arrangement of four treatments to determine the effect of spermatozoa per dose (0.5 x 10(9), 1 x 10(9), or 4 x 10(9) IUI, and 4 x 10(9) with a conventional catheter) on the main effects of conception, litter size, and farrowing rate. Following weaning at approximately 18 d after parturition, estrus detection was performed daily in the presence of a mature boar. At the time of estrus detection, sows were blocked for parity (1, 2, or 3+), weaning-to-estrus interval (WEI; 3, 4, or 5 d), and assigned randomly to be serviced twice with semen from the same boar(s). Treatment services were equally divided among three technicians. Delivery of acceptable numbers of spermatozoa per dose with either device (IUI or conventional) produced similar reproductive performances; however, farrowing rate, total pigs born, and total born alive decreased (P < 0.05) when suboptimal numbers (< or = 1 x 10(9)) of spermatozoa were used with IUI. Treatment interactions with parity were not detected and were removed from the final model. Treatment interactions with WEI on farrowing rate were detected (P < 0.05), and sows with WEI of 3 d had a markedly lower (P < 0.05) farrowing rate than all other treatment groups. The results from this experiment suggest that placement of semen at the beginning of the uterine horn with conventional volumes and spermatozoa numbers produces results similar to placement of semen in the cervical cavity with a conventional AI catheter. Although there is little published evidence of reproductive performances in a commercial setting with suboptimal numbers of spermatozoa, these results suggest that insemination beyond the cervix does not offset effects of suboptimal numbers of spermatozoa.
Because porcine reproductive and respiratory syndrome virus (PRRSV) can be transmitted through semen, PRRSV-free boar studs need to be routinely monitored to rapidly detect any potential PRRSV introduction. However, current protocols for monitoring PRRSV in boar studs are diverse, sometimes very costly, and their effectiveness has not been quantified. The objective of this study was to evaluate the ability of different monitoring protocols to detect PRRSV introduction into a negative boar stud by using a simulation modeling approach. A stochastic transmission model was constructed to simulate the spread of PRRSV in a typical negative boar stud in the USA (herd size of 200 boars, 60% annual replacement) and the performance of monitoring protocols by using different sample sizes (10, 30, and 60 samples), sampling frequency (3 times a week, weekly, and biweekly), and diagnostic procedures (PCR on semen, PCR on serum, ELISA on serum, and both PCR and ELISA on serum). The monitoring protocols were evaluated in terms of the time from PRRSV introduction into the boar stud to PRRSV detection. Protocols that used PCR on serum detected the PRRSV introduction earlier than protocols that used PCR on semen, and these were earlier than those that used ELISA on serum. The most intensive protocol evaluated (testing 60 boars 3 times a week by PCR on serum) would need 13 days to detect 95% of the PRRSV introductions. These results support field observations, suggesting that an intensive monitoring protocol needs to be in place in a boar stud to quickly detect a PRRSV introduction.
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