Effect of haylage and monensin supplementation on ruminal bacterial communities of feedlot cattle.

The objective of this study was to investigate the ruminal bacterial communities as affected by monensin, haylage, and their interaction of feedlot cattle fed 60 % dried distillers grains with solubles in a replicated 4 × 4 Latin square design. Pyrosequencing analysis of the V1-V3 region (about 500 bp) of 16S rRNA gene from the four dietary treatments (3 treatment plus one control diets) collectively revealed 51 genera of bacteria within 11 phyla. Firmicutes and Bacteroidetes were the first and the second most predominant phyla, respectively, irrespective of the dietary treatments. Monensin supplementation decreased the proportion of Gram-positive Firmicutes while increasing that of Gram-negative Bacteroidetes. However, the monensin supplementation did not reduce the proportion of all genera of Gram-positive bacteria placed within Firmicutes and lowered that of some genera of Gram-negative bacteria placed within Bacteroidetes. Haylage supplementation appeared to attenuate inhibition of monensin on some genera of bacteria. Factors other than monensin and haylage could affect ruminal bacterial communities.

Effects of dietary vitamin A content on antibody responses of feedlot calves inoculated intramuscularly with an inactivated bovine coronavirus vaccine.

OBJECTIVE: To investigate effects of low dietary vitamin A content on antibody responses in feedlot calves inoculated with an inactivated bovine coronavirus (BCoV) vaccine. ANIMALS: 40 feedlot calves. PROCEDURES: Calves were fed diets containing high (3,300 U/kg) or low (1,100 U/kg) amounts of vitamin A beginning on the day of arrival at a feedlot (day 0) and continuing daily until the end of the study (day 140). Serum retinol concentrations were evaluated in blood samples obtained throughout the study. Calves were inoculated IM with an inactivated BCoV vaccine on days 112 and 126. Blood samples obtained on days 112 and 140 were used for assessment of BCoV-specific serum IgG1, IgG2, IgM, and IgA titers via an ELISA. RESULTS: The low vitamin A diet reduced serum retinol concentrations between days 112 and 140. After the BCoV inoculation and booster injections, predominantly serum IgG1 antibodies were induced in calves fed the high vitamin A diet; however, IgG1 titers were compromised at day 140 in calves fed the low vitamin A diet. Other isotype antibodies specific for BCoV were not affected by the low vitamin A diet. CONCLUSIONS AND CLINICAL RELEVANCE: Dietary vitamin A restriction increases marbling in feedlot cattle; however, its effect on antibody responses to vaccines is unknown. A low vitamin A diet compromised the serum IgG1 responses against inactivated BCoV vaccine, which suggested suppressed T-helper 2-associated antibody (IgG1) responses. Thus, low vitamin A diets may compromise the effectiveness of viral vaccines and render calves more susceptible to infectious disease.

A randomized controlled trial to assess the impact of dietary energy sources, feed supplements, and the presence of super-shedders on the detection of Escherichia coli O157:H7 in feedlot cattle using different diagnostic procedures.

Alteration of the gastro-intestinal tract through manipulation of cattle diets has been proposed as a preharvest control measure to reduce fecal shedding of Escherichia coli O157:H7. The objective of this study was to examine the effects of the energy source's moisture content (high moisture corn and dry whole-shelled corn), two natural feed supplements (Saccaromyces cerevisiae boulardii CNCM 1079-Levucell and Aspergillus oryzae-Amaferm), and two levels of vitamin A (2200 IU/kg and no supplementation) on the fecal excretion of E. coli O157:H7 in naturally infected cattle. One hundred sixty-eight Angus-cross beef steers were randomly allocated to 24 pens, and each pen was assigned 1 of 12 dietary treatments in a randomized complete block design. E. coli O157:H7 was detected by rectoanal mucosal swab (RAMS) and fecal grab samples using immunomagnetic separation (IMS) and standard microbiological techniques. On the basis of multivariable multilevel logistic regression models, we found a statistically significant (p < 0.05) increase in the prevalence of E. coli O157:H7 in animals fed dry whole-shelled corn in models based on fecal-IMS, and this effect was increased if a super-shedding animal (shedding > 10(4) colony forming units of E. coli O157:H7 per gram of feces) was present in the pen at the time of testing relative to animals fed high moisture corn and nonexposed to super-shedders. However, in similar models based on RAMS-IMS testing, the effect of corn type on the prevalence of E. coli O157:H7 varied with the type of feed additive used. Being exposed to a super-shedding pen-mate also increased the odds of being positive to E. coli O157:H7 in the RAMS-IMS models. These models demonstrate that the impact of different supplements may vary with the diagnostic test used, and that further research into the biological significance of differences between RAMS- and fecal-IMS test results is warranted.