Effects of wet corn distillers grains with solubles on visceral organ mass, trace mineral status, and polioencephalomalacia biomarkers of individually-fed cattle.

Twenty-four steers (initial BW = 385 ± 1.1 kg) were blocked by BW and randomly assigned to 3 dietary treatments (0, 30, or 60% wet distillers grains with solubles [WDGS]; DM basis) and were fed individually to determine the effect of WDGS on live growth and carcass performance, visceral organ mass, trace mineral status, and polioencephalomalacia biomarkers. Steers were slaughtered at 125, 150, 164, and 192 d (2 blocks/slaughter date) when external fat depth was approximately 1.3 cm based on visual appraisal. Steers fed 30% WDGS had greater DMI than those fed 0 or 60% WDGS (P < 0.05), and steers fed 60% WDGS had the lowest carcass-adjusted ADG (P < 0.09) of the 3 treatments. Nonetheless, WDGS concentration did not alter feed efficiency (P > 0.41) on either live or carcass-adjusted basis. Steers fed 30% WDGS had greater liver S and Mn concentrations (DM basis) and lower liver Fe concentrations than control steers (P < 0.10; initial values used as a covariate), and feeding 60% WDGS decreased liver Cu and increased liver Fe (P < 0.10) compared with feeding 30% WDGS. Cytochrome c oxidase (COX) activity in brain tissue tended to be decreased with 60 vs. 30% WDGS (P = 0.12), and COX activity decreased linearly (P = 0.06) in lung tissue as dietary WDGS concentration increased. Likewise, gut fill linearly increased (P = 0.01) with increasing WDGS concentration. Feeding 30% WDGS increased fractional mass (g/kg of empty BW) of the small intestine (P < 0.10) compared with controls, whereas 60% WDGS increased fractional kidney mass (P < 0.10) compared with 30% WDGS. Overall, results suggest that gut fill, Cu status, and COX activity seem to be compromised by WDGS when fed at 60% of diet DM in diets based on steam-flaked corn, which suggests a greater susceptibility to polioencephalomalacia.

Prevalence, severity, and relationships of lung lesions, liver abnormalities, and rumen health scores measured at slaughter in beef cattle.

An array of management tools exists within the beef industry to improve animal welfare and productivity; however, the ability to assess the outcomes of these tools is needed. Deficiencies in management commonly manifest as bovine respiratory disease complex or nutritional disorders such as acidosis; therefore, lung, liver, and rumen gross pathology lesions present at slaughter were measured as part of the Harvest Audit Program (HAP) and associations with performance determined. Individual gross pathology data from 19,229 cattle at commercial packing plants in Kansas and Texas were collected. Corresponding individual preharvest and carcass data were obtained on a subset of 13,226 cattle. Associations between lesions and performance were modeled using multivariable mixed effect models. Regression coefficients were used for estimation of lesion associative effects on continuous outcomes and odds ratios for dichotomous outcomes. Across the entire population, 67.3% of the cattle had no pulmonary lesions; 22.5 and 9.8% of cattle displayed mild and severe lesions, respectively. Severe pulmonary lesions were associated with a decreased ADG of 0.07 kg and a HCW 7.1 kg less than cohorts with no pulmonary lesions (P < 0.01). Overall, 68.6% of cattle observed had normal livers. Of cattle severely affected by liver abscesses (A+; 4.6%), 14.9% also displayed severe pulmonary lesions and 28.3% displayed mild pulmonary lesions. Rumenitis lesions were observed in 24.1% of the overall study population. Of cattle with mildly abscessed livers (A-), moderately abscessed livers (A), and severely abscessed livers, 20.6, 21.6, and 9.24% displayed mild or severe rumenitis lesions at slaughter. Severe rumenitis lesions were associated with a significant decrease in ADG and HCW (0.025 and 2.20 kg, respectively; P < 0.001). Although the majority of the cattle in this population would be considered low risk, after adjustments for cattle with multiple lesions, 22.9% of cattle in the overall population were observed with a severe lesion (lung, liver, or rumen). In conclusion, a gross pathology monitoring system is feasible and the 22.9% prevalence of severe lesions (lung, liver, or rumen) indicates that significant opportunity exists to improve beef cattle health, well-being, and productivity. Data generated using HAP may be used to support decisions concerning the implementation or removal of managerial practices and health interventions in beef cattle production systems.

Effect of classifying disease states in genetic association studies for paratuberculosis.

Genetic association studies are a means to elucidate underlying genetic regulation of host-pathogen interaction, immune response, and the fate of infection. Diseases such as paratuberculosis in cattle lack definitive diagnostic criteria, thereby complicating the definition of infection status as an outcome for genetic association studies. A study was performed to evaluate the potential bias in estimates of effect and differences in statistical power associated with parallel test interpretation, latent probability of infection adjusted for imperfect test sensitivity and specificity, and multinomial outcomes in cohorts of cattle simulated using Monte Carlo sampling methods. Test results were simulated for microbial culture of feces for Mycobacterium avium subsp. paratuberculosis (MAP) and serum ELISA for anti-MAP antibody using estimates of test sensitivity and specificity. A range of disease allele frequencies and levels of association were considered. Case-control study populations were drawn from the simulated cohorts and the association between the disease allele and infection status was evaluated using logistic regression for binary outcomes and polytomous regression for multinomial outcomes. For the majority of the classification and analytical methods evaluated, estimates of effect were biased toward the null. Frequentist approaches to analysis of the latent probability of infection and multinomial classifications based upon results of culture of feces for MAP demonstrated the smallest degree of bias. Power to detect associations was generally low for all models, but improved with larger effects and higher allele frequencies. Imperfect specificity of serum ELISA was a major factor in the degree of bias observed and statistical power. The results of this study indicate that the method of classifying infection status must be considered carefully in genetic association studies for paratuberculosis and other diseases with similar challenges in defining infection status, and study designs should be modified to accommodate relative advantages and disadvantages of available methods.

Technical note: Analysis of ordinal outcomes from carcass data in beef cattle research.

Beef cattle research commonly uses Yield grade (YG) and Quality grade (QG) as outcomes in nutrition and health experiments. These outcomes, as commonly reported and analyzed, are ordinal variables with an assumed rank derived from an underlying latent variable that may or may not be available for analysis. The objective of this study was to employ mixed-effects ordinal regression and approaches previously reported in animal science and veterinary literature such as contingency table analysis, mixed-effects linear regression, and mixed-effects logistic regression for the analysis of YG and QG data and to compare results with respect to statistical significance and estimated statistical power. Five randomized complete block design experiments were used for initial evaluation. Simulated data sets were used for evaluation of relative differences in statistical power. Scenarios were observed where all of the methods differed in estimate of effect and statistical significance. Power to detect an association was similar between studies under the scenario evaluated. Ordinal regression approaches provide an estimate of effect that can be used in subsequent prediction of performance, which is an advantage over contingency table approaches that only report statistical significance. Further, ordinal models do not require modification of the outcome variable as in logistic regression or assumptions regarding YG or QG distribution in linear regression, which are often not met. Researchers faced with analysis of YG and QG data should consider the use of ordinal regression, particularly with recent advances in statistical software packages capable of implementing this method for data within hierarchical models.

Familial and herd-level associations with paratuberculosis enzyme-linked immunosorbent assay status in beef cattle.

A cross-sectional study was performed to determine the odds of having a positive paratuberculosis ELISA result if the dam was ELISA positive in Texas beef cattle, adjusted for individual and herd-level risk factors for seropositivity. Texas beef cattle (n = 2,621) were tested for paratuberculosis by using a commercial ELISA and microbiologic culture of feces for Mycobacterium avium subsp. paratuberculosis (MAP). Pedigree data were collected to identify dam-and sire-offspring pairs. Bayesian mixed-effects logistic regression was used to estimate the odds of seropositivity associated with age, dam ELISA status, sire ELISA status, herd size, herd history of clinical paratuberculosis, within-herd seroprevalence, within-herd fecal MAP prevalence, and within-herd fecal non-MAP Mycobacterium spp. prevalence. Herd of residence was included as a random effect to account for the correlation of observations within the same herd. Statistically probable associations were observed between ELISA status and herd fecal MAP prevalence [OR (odds ratio) 1.28 per 1% increase; P < 0.001] and herd seroprevalence (OR 1.21 per 1% increase; P < 0.001). The association with dam ELISA status was small (OR 1.35) and not highly probable (P = 0.69). Results indicate that use of dam ELISA status to make culling decisions in beef cattle may not improve the success of paratuberculosis control programs. Alternative strategies may be more effective for reducing the odds of seropositivity.