Sensitivity and specificity of bacterial culture, qPCR, and somatic cell count for detection of goats with Staphylococcus aureus intramammary infection using Bayesian latent class models.

Staphylococcus aureus (S. aureus) is an important udder pathogen affecting goat milk production. The ability to detect goats with subclinical mastitis caused by S. aureus is essential in udder health control programs. In Norway, the industry recommends using somatic cell count (SCC) as a screening tool, and conventional bacterial culture (BC) as a confirmatory test for goat milk samples, but a commercial qPCR, Mastitis 4 qPCR (DNA Diagnostics, Risskov, Denmark) is also available. However, few studies have validated the use of these methods for the detection of goats with S. aureus intramammary infection (IMI). Therefore, the objective of this retrospective study was to estimate the diagnostic sensitivity and specificity of BC, qPCR, and SCC for the detection of goats with IMI caused by S. aureus using Bayesian latent class analysis. We analyzed the BC and qPCR results of aseptically collected milk samples and SCC results from milk recording samples from 319 goats from three herds using different SCC cut-offs. At a SCC cut-off of 2000,000 cells/mL, the estimated median prevalence in each herd was 12.7% (95% highest posterior density credible interval [CI] 6.5-19.8), 15.7% (95% CI 9.3-23.0), and 1.5% (95% CI 0.0-4.3). The median sensitivity was 93.0% (95% CI 80.2-100), 93.6% (95% CI 82.3-100) and 78.2% (95% CI 62.3-91.2) for BC, qPCR, and SCC, respectively. The estimated median specificity of BC was 99.5% (99% CI 98.4-100), for qPCR, 98.9% (95% CI 97.5-100), and for SCC 61.5% (95% CI 56.0-67.1). The results show that BC, which is today's standard method for diagnosing IMI, has a high accuracy for detection of goats with S. aureus IMI, but qPCR had a sensitivity and specificity similar to BC, and may act as an alternative.

Salivary IgG levels in neonatal calves and its association to serum IgG: an observational pilot study.

The diagnosis of inadequate transfer of colostrum immunoglobulin G (IgG) to calf serum, often known as failure of passive transfer (<10 g/L IgG1 at 24 to 48 h), necessitates blood sampling from the calf and in some instances the presence of a veterinarian. Sampling saliva is both less invasive and easy for the producer. Previous research has shown that quantification of saliva IgG is possible in juvenile and adult cattle. The objectives of this observational pilot study were to investigate whether IgG can be quantified in neonatal calf saliva, if it is correlated to serum IgG concentrations, and if the indirect quantification of saliva IgG is achievable by use of a digital refractometer. Paired blood and saliva samples were collected from 20 healthy dairy calves aged 1 to 3 d. In these samples, IgG was quantified directly with single radial immunodiffusion and indirectly by use of a digital refractometer indicating Brix % (a subsample of n = 12 saliva samples). A strong positive correlation (r = 0.7, P < 0.001) between saliva IgG (mean ± SD; 0.2 ± 0.11 g/L) and serum IgG (32.1 ± 11.94 g/L) was found. Saliva IgG ranged from the lowest detectable value, 0.1 g/L (n = 6 samples) to 0.6 g/L. Saliva Brix (1.2 ± 0.69%) was not significantly correlated to serum IgG (n = 12, r = 0.43, P = 0.155); however, it was significantly correlated to saliva IgG (n = 12, r = 0.7, P = 0.018) and Brix in serum (n = 12, r = 0.7, P = 0.013). We conclude that IgG was quantifiable in most of the saliva samples. For saliva IgG to be of any value with regards to detecting failure of passive transfer, future studies should investigate methods that can detect IgG <0.1 g/L. The results indicate that saliva IgG can be used to predict serum IgG at levels above 10 g/L, which may warrant further exploration of the use of saliva in the surveillance of failure of passive transfer. The results of the current pilot study did not support the potential usage of a Brix % refractometer to quantify saliva IgG.