Accuracy of direct and indirect methods for assessing bovine colostrum quality using a latent class model fit within a Bayesian framework

Impacts of preweaning colostrum feeding practices and health measures on dairy cow production, while accounting for genetic potential

Calf management and health are essential for setting up the foundation of a productive cow. The objectives of this study were to estimate the impact of preweaning practices on milk production parameters while accounting for an animal's genetic potential in New Brunswick, Canada. A retrospective cohort study was performed on 220 heifer calves from eight herds born in 2014-2015. Preweaning practices and health data were recorded by producers and reviewed by the herd veterinarian for each calf. The herd veterinarian also visited the farms to collect serum samples from calves and frozen colostrum samples. The production outcomes assessed were milk, protein and fat yields, standardized to 305 d for the first lactation (L1) and a combined group of lactations two and three (L2 + 3). The genomic potential was determined as genomic parent averages (GPA) for the associated production parameters. Analysis was performed with multivariable linear (L1) and linear mixed (L2 + 3) regression models. In L1, for every 1.0 kg increase in weaning weight, milk, protein, and fat yield increased by 25.5, 0.82, and 1.01 kg, respectively (P < 0.006). Colostrum feeding time (CFT) positively impacted L1 milk and protein production, with feeding between 1-2 h of life producing the greatest estimates of 626 kg of milk and 18.2 kg of protein yield (P < 0.007), compared to earlier or later CFT. Fat yield production was decreased by 80.5 kg (P < 0.006) in L1 when evaluating animals that developed a preweaning disease and were not treated with antibiotics compared to healthy untreated animals. Impacts on L2 + 3 were similar across all production outcomes, with a positive interaction effect of CFT and weaning weight. Compared to CFT < 1 h, the later CFT groups of 1-2 h and > 2 h produced greater yield outcomes of 68.2 to 72.6 kg for milk (P < 0.006), 2.06 to 2.15 kg for protein (P < 0.005), and 1.8 to 1.9 kg for fat (P < 0.045) for every 1 kg increase of weaning weight, respectively. The fit of all models was significantly improved with the inclusion of GPA. These results indicate that colostrum management and preweaning health measures impacted production parameters as adults. The inclusion of GPA significantly improved the accuracy of the models, indicating that this can be an important parameter to include in future studies.

Bayesian estimation of sensitivity and specificity of fecal culture, fecal PCR and serum ELISA for diagnosis of Mycobacterium avium subsp. paratuberculosis infections in sheep

The objective of the present study was to evaluate the diagnostic accuracy of the individual fecal culture (IFC), fecal PCR (FPCR), and serum ELISA for the detection of Mycobacterium avium subsp. paratuberculosis (MAP) infections in sheep from four governorates in Egypt, using a latent class model (LCM) fitted within a Bayesian framework. Furthermore, the within-governorate prevalence of MAP infection in sheep was estimated as a secondary objective. Fecal and blood samples were collected from 370 sheep in four Egyptian governorates. Fecal samples were analyzed by IFC and RT-PCR based on ISMav2 gene, while ELISA was performed on serum samples. The sensitivity (Se) and specificity (Sp) of the three diagnostic tests were estimated using a three-tests-four-populations Bayesian LCM to obtain posterior estimates [medians and 95% Bayesian credible intervals (95% BCI)] for each parameter. The median Se estimates (95% BCI) for IFC, FPCR, and serum ELISA were 31.8% (22.8-41.4), 49.7% (31.8-79.9), and 61.2% (39.8-81.4), respectively. The median Sp estimates (95% BCI) for IFC, FPCR, and serum ELISA were 97.7% (96.1-98.9), 97.7% (95.6-99.5), and 98.4% (96.9-99.3), respectively. The median within-governorate paratuberculosis prevalence (95% BCI) was 5.2% (1.1-13.6), 8.4% (2.9-17.7), 9.4% (3.0-20.7), and 18.2% (10.5-29.5) for the Gharbia, Menoufia, Qalyubia, and Kafr El-Sheikh governorates, respectively. In conclusion, at a ratio of the optical density (OD) sample/OD positive control threshold of > 45%, ELISA showed the highest Se among the three tests and comparable Sp to IFC and FPCR. The test ELISA evaluated in this study is an interesting alternative for detecting MAP in sheep due to its higher Se, lower cost, and shorter turnaround laboratory time compared to IFC and FPCR.