Energy Expenditure in Growing Heifers with Divergent Residual Feed Intake Phenotypes. Effects and Interaction of Metaphylactic Treatment and Temperament on Receiving Steers

Cattle classified as having low residual feed intake (RFI) phenotypes are those that consume less feed than expected based on body weight and growth performance. Mechanisms contributing to the variation in RFI are not fully understood. Previous studies have shown that cattle of divergent RFI phenotypes have different levels of energy expenditures, which are associated with heat increment, basal metabolism, thermoregulation responses, and physical activity. The objectives of this experiment were to characterize residual feed intake (RFI) in growing heifers and to determine if variation in whole-animal energy expenditure contributes to differences in RFI. Brangus heifers (n =120) were individually fed a roughage-based diet (1.93 Mcal ME/kg DM) diet twice daily and feed refusals measured weekly. Heifers were weighed once weekly for 70 d and RFI calculated as the difference between actual and expected DMI from linear regression of DMI on ADG and mid-test BW0.75. Immediately following the 70 d study, oxygen pulse rate (mL O2/heart beat) and 48-h heart rates were measured on 8 high and 8 low RFI heifers to estimate energy expenditure. Daily heart rates and oxygen pulse rates were higher (P < 0.05) in heifers with high RFI compared to those with low RFI. As a result, energy expenditure (kcal/BW0.75) was estimated to be 17.4 percent greater (P < 0.05) in high-RFI heifers then low-RFI heifers. Mortality and morbidity losses caused by bovine respiratory disease (BRD) continue to negatively impact the net revenues of the beef cattle industry. Stress can predispose calves arriving at feedlots to BRD by impairing their immune system with calves having more excitable temperaments possibly having a greater risk. The objectives of the second study was to examine the effects of metaphylactic treatment and temperament on performance, feed intake, feed efficiency, and feeding behavior traits in steers. Santa Gertrudis steers (n =119) were weighed and randomly to control (CON; no antimicrobial treatment) or metaphylactic (MET; 1.5 mL/45 kg BW of ceftiofur crystalline free acid) treatments. Steers were weighed at 14-d intervals and individual intakes and feeding behavior traits measured using a GrowSafe sytems while fed a roughage-based diet (2.21 Mcal ME/kg DM). Objective (relative exit velocity; REV) and subjective (chute score; CS) measurements of temperament were measured on arrival and on day 28 of the study. Steers with higher REV weighed less, grew slower, consumed less feed, spent less time consuming feeding, had more feeding bouts per meal, had less backfat, smaller longissimus muscle area, and higher cortisol levels. Steers treated with MET had higher ADG than those receiving CON. Cattle with higher REV that received MET had less of a decrease in ADG, DMI, time spend consuming feed, and less of an increase in feeding bouts compared to high REV steers receiving CON. Results from this study suggest that process-control strategies, which quantify and manage inter-animal variation in calf temperament may facilitate more judicious use of antimicrobial products and provide more consistent and predictable responses to metaphylactic strategies

Escherichia coli O26 in feedlot cattle: Fecal prevalence, isolation, characterization, and effects of an E. coli O157 vaccine and a direct-fed microbial

Escherichia coli O26 is second only to O157 in causing foodborne, Shiga toxin–producing E. coli (STEC) infections. Our objectives were to determine fecal prevalence and characteristics of E. coli O26 in commercial feedlot cattle (17,148) that were enrolled in a study to evaluate an E. coli O157:H7 siderophore receptor and porin (SRP®) vaccine (VAC) and a direct-fed microbial (DFM; 106 colony-forming units [CFU]/animal/day of Lactobacillus acidophilus and 109 CFU/animal/day of Propionibacterium freudenreichii). Cattle were randomly allocated to 40 pens within 10 complete blocks; pens were randomly assigned to control, VAC, DFM, or VAC+DFM treatments. Vaccine was administered on days 0 and 21, and DFM was fed throughout the study. Pen-floor fecal samples (30/pen) were collected weekly for the last 4 study weeks. Samples were enriched in E. coli broth and subjected to a multiplex polymerase chain reaction (PCR) designed to detect O26-specific wzx gene and four major virulence genes (stx1, stx2, eae, and ehxA) and to a culture-based procedure that involved immunomagnetic separation and plating on MacConkey agar. Ten presumptive E. coli colonies were randomly picked, pooled, and tested by the multiplex PCR. Pooled colonies positive for O26 serogroup were streaked on sorbose MacConkey agar, and 10 randomly picked colonies per sample were tested individually by the multiplex PCR. The overall prevalence of E. coli O26 was higher (p<0.001) by the culture-based method compared to the PCR assay (22.7 versus 10.5%). The interventions (VAC and or DFM) had no impact on fecal shedding of O26. Serogroup O26 was recovered in pure culture from 23.9% (260 of 1089) of O26 PCR-positive pooled colonies. Only 7 of the 260 isolates were positive for the stx gene and 90.1% of the isolates possessed an eaeβ gene that codes for intimin subtype β, but not the bfpA gene, which codes for bundle-forming pilus. Therefore, the majority of the O26 recovered from feedlot cattle feces was atypical enteropathogenic E. coli, and not STEC

Shiga toxin producing Escherichia coli (STEC) in cattle: factors affecting fecal shedding of E. coli O157:H7 and detection methods of non-O157 STEC

Doctor of PhilosophyDepartment of Diagnostic Medicine/PathobiologyT. G. NagarajaEscherichia coli O157:H7 and over 380 non-O157 serotypes of Shiga toxin producing E. coli (STEC) are human food-borne pathogens that inhabit the hindgut of ruminants and are shed in the feces, which subsequently contaminate food products. Recent epidemiological data have shown that six non-O157 STEC (O26, O103, O111, O121, O45 and O145) account for majority of human STEC infections. Fecal shedding of STEC is influenced by a number of factors, including diets, supplements, and feed additives, because of their potential to alter hindgut ecosystem. Not much is known about the fecal shedding of non-O157 STEC in cattle because of lack of standardized detection methods. Fecal shedding of E. coli O157:H7 was studied to determine the effects of supplemental urea, monensin, an ionophore, and ractopamine, a beta-agonist. Cattle fed monensin at 44 mg/kg of feed had lower (P = 0.05) fecal O157:H7 prevalence than cattle fed 33 mg/kg. Supplemental urea (0.35 or 0.70% of the diet) and inclusion of ractopamine at 200 mg/animal/day had no effect on fecal shedding of E. coli O157:H7. In an experimental inoculation study, inclusion of corn starch to a distiller’s grains (DG)-supplemented diet had no effect on fecal shedding of E. coli O157 suggesting that either the decreased starch content in the DG-supplemented diet is not a factor in the increased shedding of E. coli O157:H7 or inclusion of pure starch in the diet may not have achieved our intended goal to have starch flow into the hindgut similar to that of corn grain. A multiplex PCR to detect O26, O45, O103, O111, O121, O145, and O157 was designed and applicability to detect the seven serogroups in cattle feces was evaluated. A multiplex PCR, designed to detect E. coli O104, feces showed presence of O104 in cattle feces (20.6%), but the isolated strains did not carry genes characteristic of the virulent strain responsible for the 2011 food-borne outbreak in Germany. Two preharvest interventions, a siderophore receptor and porin proteins-based vaccine and a Lactobacillus acidophilus-based direct-fed microbial, intended to control E. coli O157, had no effect on fecal shedding of O26 assessed by culture-based or PCR-based method

Shiga toxin producing Escherichia coli (STEC) in cattle: factors affecting fecal shedding of E. coli O157:H7 and detection methods of non-O157 STEC

Doctor of PhilosophyDepartment of Diagnostic Medicine/PathobiologyT. G. NagarajaEscherichia coli O157:H7 and over 380 non-O157 serotypes of Shiga toxin producing E. coli (STEC) are human food-borne pathogens that inhabit the hindgut of ruminants and are shed in the feces, which subsequently contaminate food products. Recent epidemiological data have shown that six non-O157 STEC (O26, O103, O111, O121, O45 and O145) account for majority of human STEC infections. Fecal shedding of STEC is influenced by a number of factors, including diets, supplements, and feed additives, because of their potential to alter hindgut ecosystem. Not much is known about the fecal shedding of non-O157 STEC in cattle because of lack of standardized detection methods. Fecal shedding of E. coli O157:H7 was studied to determine the effects of supplemental urea, monensin, an ionophore, and ractopamine, a beta-agonist. Cattle fed monensin at 44 mg/kg of feed had lower (P = 0.05) fecal O157:H7 prevalence than cattle fed 33 mg/kg. Supplemental urea (0.35 or 0.70% of the diet) and inclusion of ractopamine at 200 mg/animal/day had no effect on fecal shedding of E. coli O157:H7. In an experimental inoculation study, inclusion of corn starch to a distiller’s grains (DG)-supplemented diet had no effect on fecal shedding of E. coli O157 suggesting that either the decreased starch content in the DG-supplemented diet is not a factor in the increased shedding of E. coli O157:H7 or inclusion of pure starch in the diet may not have achieved our intended goal to have starch flow into the hindgut similar to that of corn grain. A multiplex PCR to detect O26, O45, O103, O111, O121, O145, and O157 was designed and applicability to detect the seven serogroups in cattle feces was evaluated. A multiplex PCR, designed to detect E. coli O104, feces showed presence of O104 in cattle feces (20.6%), but the isolated strains did not carry genes characteristic of the virulent strain responsible for the 2011 food-borne outbreak in Germany. Two preharvest interventions, a siderophore receptor and porin proteins-based vaccine and a Lactobacillus acidophilus-based direct-fed microbial, intended to control E. coli O157, had no effect on fecal shedding of O26 assessed by culture-based or PCR-based method

Applicability of a multiplex PCR to detect O26, O45, O103, O111, O121, O145, and O157 serogroups of Escherichia coli in cattle feces

Shiga toxin-producing Escherichia coli (STEC), particularly O157, are major food borne pathogens. Non-O157 STEC, particularly O26, O45, O103, O111, O121, and O145, have also been recognized as a major public health concern. Unlike O157, detection procedures for non-O157 have not been fully developed. Our objective was to develop a multiplex PCR to distinguish O157 and the ‘top six’ non-O157 serogroups (O26, O45, O103, O111, O121, and O145) and evaluate the applicability of the multiplex PCR to detect the seven serogroups of E. coli in cattle feces. Published sequences of O-specific antigen coding genes, rfbE (O157) and wzx and wbqE-F (non-O157), were analyzed to design serogroup-specific primers. The specificity of amplifications was confirmed with 138 known STEC strains and the reaction yielded the expected amplicons for each serogroup. In feces spiked with pooled 7 STEC strains, the sensitivity of the detection was 4.1 X 10[superscript]5 CFU/g before enrichment and 2.3 X 10[superscript]2 after 6 h enrichment in E. coli broth. Additionally, 216 fecal samples from cattle were collected and tested by multiplex PCR and cultural methods. The multiplex PCR revealed a high prevalence of all seven serogroups (178 [O26], 108 [O45], 149 [O103], 30 [O111], 103 [O121], 5 [O145], and 160 [O157]) of 216 samples in fecal samples. Cultural procedures identified 33.1% (53/160) and 35.5% (11/31) of PCR-positive samples for E. coli O157 and non-O157 serogroups, respectively. Samples that were culture-positive were all positive by the multiplex PCR. The multiplex PCR can be used to identify serogroups of putative STEC isolates