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Seventy-four beef heifers were used to evaluate relationships among performance, residual feed intake (RFI), and temperament measured as growing heifers (Phase 1) and subsequently as 3-yr-old lactating beef cows (Phase 2) in the same cohort. In both phases, females were housed in a covered facility and fed similar forage-based diets, and individual feed intakes, BW, BCS, chute scores (CS), exit velocities (EV), and pen scores (PS) were collected throughout the 70-d feeding trials. In Phase 2, cows were milked on trial d 14 (lactation d 28 ± 3.5) and trial d 70 (lactation d 84 ± 3.5) to determine ener- gy-corrected milk (ECM) production. Ultrasonic backfat thickness (BF), and ribeye area (REA) were evaluated on d 0 and 70 of the trial in Phase 2. Heifers were ranked by RFI and placed into Low ( 0.5 SD mean RFI; n = 24) RFI groups. Body weight, BCS, and ADG were similar among all RFI groups; however, daily DMI differed for all groups (P 0.1) between RFI and temperament. Phase 1 CS was negatively associated with ADG in Phase 1 (r = -0.28; P = 0.02) and 2 (r = -0.32; P = 0.01), and positively associated with d 14 (r = 0.24; P = 0.04) and 70 (r = 0.25; P = 0.03) ECM. Phase 2 CS was negatively associated with Phase 2 ADG (r = -0.29; P = 0.01) and positively associated with d 14 (r = 0.46; P = 0.001) and 70 (r = 0.33; P = 0.004) ECM. Phase 2 PS also tended to be negatively associated with DMI in Phase 1 (r = -0.20; P = 0.096) and 2 (r = -0.20; P = 0.08). In this study, heifers that were most feed effi cient subsequently consumed less feed as lactating cows and maintained similar performance. Feed effi ciency was not associated with differences in temperament; however, more excitable females had poorer BW gains and tended to have reduced feed intakes but produced more ECM.

Two experiments were conducted to determine the effect of calf removal (CR) on pregnancy rate (PR) and calf performance in suckled beef cows. Cows in both experiments were synchronized with the 7-d CO-Synch + CIDR protocol [i.e., 100-µg injection of GnRH at controlled internal drug release (CIDR) device insertion (d -7) with 25-mg injection of PGF2α at CIDR removal (d 0), followed by injection of GnRH and timed AI (TAI) on d 3]. Cows were blocked by location (6 locations), stratified by days postpartum (DPP) and parity, and assigned to 1 of 2 treatments in Exp. 1: 1) control (Control; n = 156); 2) calves were separated from their dams between d 0 and 3 (CR72; n = 168); and 1 of 4 treatments in Exp. 2: 1) Control (n = 103); 2) CR72 (n = 104); 3) calves were separated from their dams between d 0 and 2 (CR48A; n = 95); and 4) similar to CR48A but CR between d 1 and 3 (CR48B; n = 53). Transrectal ultrasonography of ovarian structures was performed on d 0, 1, 2, 3, 4, and 10 (in a subset of cows) to determine pregnancy status on d 33. Blood samples were collected on d -14, -7, 0, 3, and 10 (in a subset of cows) to determine concentrations of progesterone (P4) and estradiol (E2). Calves were blocked by age as young (25 to 59 d), medium (60 to 79 d), and old (≥80 d), and were weighed on d 0, 3, 33, and 63. Overall PR did not differ among treatments and averaged 50%. Follicle growth rate from d 0 to 3 tended (P = 0.06) to be greater for CR72 (0.42 ± 0.15 mm/d) compared with Control (0.02 ± 0.15 mm/d). Young (-3.9 ± 0.3%) and old (-3.1 ± 0.4%) calves lost a greater (P < 0.001) percent of BW (PBW) during CR than medium-age (-1.6 ± 0.3%) calves exposed to CR72. In Exp. 2, PR were similar among all 3 locations (49%; P = 0.15). Young (-4.8 ± 0.6%) and medium (-3.0 ± 0.5%) calves lost greater (P < 0.01) percent body weight (PBW) during CR than old (-1.4 ± 0.6%) calves within the CR72 treatment. Calves exposed to CR48 (-2.2 ± 0.6%, -1.1 ± 0.6%, and -2.4 ± 0.6% PBW change for young, medium, and old, respectively) lost more BW than calves in the Control group (-3.7 ± 0.4%, -1.7 ± 0.5%, and -2.1 ± 0.5% PBW change for young, medium, and old, respectively). Subsequent calf weights on d 33 and 63 were greater (P < 0.05) in Controls than cows exposed to CR48 or CR72 treatments. We conclude that CR stimulated follicle growth but failed to enhance PR to TAI. However, CR had a negative impact on subsequent calf performance, which differed, depending on the duration and age of the calf when exposed to CR.

Mature dairy cattle were sampled over a 2-year period (2001-2002) on six farms in New Mexico and Texas. Fecal samples (n = 1560) were collected via rectal palpation and cultured for Salmonella, and one isolate from each positive sample was serotyped. Three isolates of each serotype, with the exception of Salmonella Newport (n = 12), were examined for susceptibility to 17 antimicrobial agents. Twenty-two different serotypes were identified from a total of 393 Salmonella isolates. Montevideo was the predominant serotype (27%) followed by Mbandaka (15%), Senftenberg (11.4%), Newport (6.4%), Anatum (4.8%), and Give (4.8%). Salmonella Typhimurium and Dublin, two frequently reported serotypes, accounted for only 1% of the observed serotypes in this study. Sixty-four percent of the serotypes were susceptible to all 17 antimicrobials, 14% were resistant to a single agent, and 22% were multiresistant (2-11 types of resistance). All isolates tested were susceptible to amikacin, apramycin, imipenem, ceftriaxone, nalidixic acid, and ciprofloxacin. The most frequent types of resistance were to sulfamethoxazole, tetracycline, streptomycin, kanamycin, chloramphenicol, and ampicillin (ranging from 8.9 to 22.4%). Serotypes demonstrating multiple resistance included Dublin and Give (resistant to three or more antibiotics), Typhimurium (resistant to five antibiotics), and Newport (four and two isolates resistant to six and nine antibiotics, respectively). Class 1 integrons were present in only two Salmonella Dublin isolates and one Salmonella Newport isolate. The most prevalent resistance patterns observed in this study were toward antimicrobial agents commonly used in cattle, while all Salmonella isolates were susceptible to ceftriaxone and ciprofloxacin, antibiotics used in human medicine.

Dried distiller's grains (DG) produced from ethanol fermentations dosed with 0 (control), 2, or 20 mg/kg virginiamycin-based product or spiked with virginiamycin (VM) postfermentation were fed to cattle and effects on antimicrobial susceptibility, and prevalence of antimicrobial resistance genes in commensal bacteria was examined. Biological activity assays of DG (from each fermentation) indicated a concentration of 0, 0.7, and 8.9 mg/kg VM, respectively. Twenty-four crossbred beef steers were fed 1 of 4 diets (containing 8% of each of the different batches of DG) and a fourth using 8% of the control DG (0 mg/kg VM) + 0.025 g/kg V-Max50 (positive control) for 7 wk. Fecal samples were collected weekly throughout the experimental period and cultured for Escherichia coli and Enterococcus, and isolates were examined for antimicrobial susceptibility, antimicrobial resistance genes (vatE, ermB, and msrC in Enterococcus), and integrons (E. coli). No treatment differences (P0.05) were observed in antimicrobial susceptibility of the E. coli isolates. Enterococcus isolates were resistant to more antimicrobials; however, this was influenced by the species of Enterococcus and not treatment (P0.10). The prevalence of ermB was greater (P0.05) in the control isolates after 4 and 6 wk while at wk 7, prevalence was greater (P0.01) in the 0.7 and 8.9 mg/kg VM treatments. Taken together, the minor treatment differences observed for the presence of ermB coupled with the lack of effect on antimicrobial susceptibility patterns suggest that feeding DG containing VM residues should have minimal if any impact on prevalence of antimicrobial resistance.

Two experiments were conducted to determine the effect of calf removal (CR) on pregnancy rate (PR) and calf performance in suckled beef cows. Cows in both experiments were synchronized with the 7-d CO-Synch + CIDR protocol [i.e., 100-µg injection of GnRH at controlled internal drug release (CIDR) device insertion (d -7) with 25-mg injection of PGF2α at CIDR removal (d 0), followed by injection of GnRH and timed AI (TAI) on d 3]. Cows were blocked by location (6 locations), stratified by days postpartum (DPP) and parity, and assigned to 1 of 2 treatments in Exp. 1: 1) control (Control; n = 156); 2) calves were separated from their dams between d 0 and 3 (CR72; n = 168); and 1 of 4 treatments in Exp. 2: 1) Control (n = 103); 2) CR72 (n = 104); 3) calves were separated from their dams between d 0 and 2 (CR48A; n = 95); and 4) similar to CR48A but CR between d 1 and 3 (CR48B; n = 53). Transrectal ultrasonography of ovarian structures was performed on d 0, 1, 2, 3, 4, and 10 (in a subset of cows) to determine pregnancy status on d 33. Blood samples were collected on d -14, -7, 0, 3, and 10 (in a subset of cows) to determine concentrations of progesterone (P4) and estradiol (E2). Calves were blocked by age as young (25 to 59 d), medium (60 to 79 d), and old (≥80 d), and were weighed on d 0, 3, 33, and 63. Overall PR did not differ among treatments and averaged 50%. Follicle growth rate from d 0 to 3 tended (P = 0.06) to be greater for CR72 (0.42 ± 0.15 mm/d) compared with Control (0.02 ± 0.15 mm/d). Young (-3.9 ± 0.3%) and old (-3.1 ± 0.4%) calves lost a greater (P0.001) percent of BW (PBW) during CR than medium-age (-1.6 ± 0.3%) calves exposed to CR72. In Exp. 2, PR were similar among all 3 locations (49%; P = 0.15). Young (-4.8 ± 0.6%) and medium (-3.0 ± 0.5%) calves lost greater (P0.01) percent body weight (PBW) during CR than old (-1.4 ± 0.6%) calves within the CR72 treatment. Calves exposed to CR48 (-2.2 ± 0.6%, -1.1 ± 0.6%, and -2.4 ± 0.6% PBW change for young, medium, and old, respectively) lost more BW than calves in the Control group (-3.7 ± 0.4%, -1.7 ± 0.5%, and -2.1 ± 0.5% PBW change for young, medium, and old, respectively). Subsequent calf weights on d 33 and 63 were greater (P0.05) in Controls than cows exposed to CR48 or CR72 treatments. We conclude that CR stimulated follicle growth but failed to enhance PR to TAI. However, CR had a negative impact on subsequent calf performance, which differed, depending on the duration and age of the calf when exposed to CR.

Seventy-four beef heifers were used to evaluate relationships among performance, residual feed intake (RFI), and temperament measured as growing heifers (Phase 1) and subsequently as 3-yr-old lactating beef cows (Phase 2) in the same cohort. In both phases, females were housed in a covered facility and fed similar forage-based diets, and individual feed intakes, BW, BCS, chute scores (CS), exit velocities (EV), and pen scores (PS) were collected throughout the 70-d feeding trials. In Phase 2, cows were milked on trial d 14 (lactation d 28 ± 3.5) and trial d 70 (lactation d 84 ± 3.5) to determine energy-corrected milk (ECM) production. Ultrasonic backfat thickness (BF), and ribeye area (REA) were evaluated on d 0 and 70 of the trial in Phase 2. Heifers were ranked by RFI and placed into Low (0.5 SD mean RFI; n = 27), Medium (within ± 0.5 SD; n = 23), and High (0.5 SD mean RFI; n = 24) RFI groups. Body weight, BCS, and ADG were similar among all RFI groups; however, daily DMI differed for all groups (P0.01) and was greater (10.76 ± 0.24 kg/d) for High, intermediate (9.88 ± 0.25 kg/d) for Medium, and less (8.52 ± 0.23 kg/d) for Low RFI heifers. When cow performance was analyzed based on RFI rank as heifers, BW, BCS, ADG, RFI, d 14 and d 70 ECM, BF, and REA were similar among RFI groups; however, cows that were most efficient as heifers (Low) had decreased (P0.05) daily DMI values (10.30 ± 0.41 kg/d) compared with cows that ranked Medium (11.60 ± 0.44 kg/d) or High (11.50 ± 0.43 kg/d) as heifers. The Pearson rank correlation between Phase 1 and 2 RFI was r = 0.13 (P = 0.30), and Pearson rank correlations showed no relationship (P0.1) between RFI and temperament. Phase 1 CS was negatively associated with ADG in Phase 1 (r = -0.28; P = 0.02) and 2 (r = -0.32; P = 0.01), and positively associated with d 14 (r = 0.24; P = 0.04) and 70 (r = 0.25; P = 0.03) ECM. Phase 2 CS was negatively associated with Phase 2 ADG (r = -0.29; P = 0.01) and positively associated with d 14 (r = 0.46; P = 0.001) and 70 (r = 0.33; P = 0.004) ECM. Phase 2 PS also tended to be negatively associated with DMI in Phase 1 (r = -0.20; P = 0.096) and 2 (r = -0.20; P = 0.08). In this study, heifers that were most feed efficient subsequently consumed less feed as lactating cows and maintained similar performance. Feed efficiency was not associated with differences in temperament; however, more excitable females had poorer BW gains and tended to have reduced feed intakes but produced more ECM.

Chlorate kills E. coli O157:H7 and has been proposed as a feed additive to be included in cattle rations immediately prior to slaughter to reduce E. coli O157: H7 populations in the gut. Antibiotic usage is not recommended in cases of E. coil O157:H7-induced hemorrhagic colitis because some antibiotics stimulate increased toxin production. This study was undertaken to determine if chlorate treatment affected toxin production. Pure cultures of E. coil O157:H7 were treated with 1/4 MIC of antibiotics (ampicillin, tetracycline, ceftiofur, gentamicin, monensin, tylosin, penicillin, ciprofloxacin, and novobiocin); toxin production was significantly increased by some antibiotics, but not by chlorate. Studies with mixed fecal bacteria demonstrated that chlorate killed E. coli O157:H7, but again did not stimulate toxin production. Chlorate appears to be an effective method to reduce shiga toxin-producing E. coil (STEC) populations in food animals, but additional studies are warranted before it is used to control infections.

Ionophores (such as monensin, lasalocid, laidlomycin, salinomycin and narasin) are antimicrobial compounds that are commonly fed to ruminant animals to improve feed efficiency. These antimicrobials specifically target the ruminal bacterial population and alter the microbial ecology of the intestinal microbial consortium, resulting in increased carbon and nitrogen retention by the animal, increasing production efficiency. Ionophores transport ions across cell membranes of susceptible bacteria, dissipating ion gradients and uncoupling energy expenditures from growth, killing these bacteria. Not all bacteria are susceptible to ionophores, and several species have been shown to develop several mechanisms of ionophore resistance. The prophylactic use of antimicrobials as growth promotants in food animals has fallen under greater scrutiny due to fears of the spread of antibiotic resistance. Because of the complexity and high degree of specificity of ionophore resistance, it appears that ionophores do not contribute to the development of antibiotic resistance to important human drugs. Therefore it appears that ionophores will continue to play a significant role in improving the efficiency of animal production in the future.

Escherichia coli O157:H7 and Salmonella are widely recognized as important agents of foodborne disease with worldwide distribution. The use of ionophores in feeding growing ruminants is widespread in the United States and has attracted recent interest due to the apparent temporal relationship between initial ionophore use and the increase in human E. coli O157:H7 cases. Two experiments were conducted to evaluate the effects of short-term feeding of ionophores on fecal shedding, intestinal concentrations, and antimicrobial susceptibility of E. coli O157:H7 and S. typhimurium in growing lambs. Sixteen lambs were used in each experiment, four lambs per treatment group: monensin, laidlomycin propionate, bambermycin, and a control treatment. Lambs were fed a grain and hay (50:50) diet with their respective ionophore for 12 d before experimental inoculation with E. coli O157:H7 or S. typhimurium. Animals were maintained on their respective diets an additional 12 d, and fecal shedding of inoculated pathogens was monitored daily. Lambs were killed and tissues and contents were sampled from the rumen, cecum, and rectum. No differences (P0.05) in fecal shedding of Salmonella or E. coli O157:H7 were observed due to treatment. Occurrence of Salmonella or E. coli in luminal contents and tissue samples from the rumen, cecum, and rectum did not differ (P0.05) among treatments. Feeding monensin decreased (P0.05) the incidence of scours in sheep infected with Salmonella compared with the other treatments. No differences in antimicrobial susceptibility were found in any of Salmonella or E. coli O157:H7 isolates. Results from these studies indicate that short-term ionophore feeding had very limited effects on E. coli and Salmonella shedding or on antimicrobial susceptibility in experimentally infected lambs.

When soluble extracts from the extreme acidophilic archaeon Sulfolobus solfataricus were incubated with [gamma-32P]ATP, several radiolabeled polypeptides were observed following SDS-PAGE. The most prominent of these migrated with apparent molecular masses of 14, 18, 35, 42, 46, 50, and 79 kDa. Phosphoamino acid analysis revealed that all of the proteins contained phosphoserine, with the exception of the 35-kDa one, whose protein-phosphate linkage proved labile to strong acid. The observed pattern of phosphorylation was influenced by the identity of the divalent metal ion cofactor used, Mg2+ versus Mn2+, and the choice of incubation temperature. The 35- and 50-kDa phosphoproteins were purified and their amino-terminal sequences determined. The former polypeptide's amino-terminal sequence closely matched a conserved portion of the alpha-subunit of succinyl-CoA synthetase, which forms an acid-labile phosphohistidyl enzyme intermediate during its catalytic cycle. This identification was confirmed by the ability of succinate or ADP to specifically remove the radiolabel. The 50-kDa polypeptide's sequence contained a heptapeptide motif, Phe/Pro-Gly-Thr-Asp/Ser-Gly-Val/Leu-Arg, found in a similar position in several hexosephosphate mutases. The catalytic mechanism of these mutases involves formation of a phosphoseryl enzyme intermediate. The identity of p50 as a hexosephosphate mutase was confirmed by (1) the ability of sugars and sugar phosphates to induce removal of the labeled phosphoryl group from the protein, and (2) the ability of [32P]glucose 6-phosphate to donate its phosphoryl group to the protein.

Mutant 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductases of the halophilic archaeon Haloferax volcanii were constructed to test the proposed mechanism that phosphorylation downregulates the activity of higher eukarya HMG-CoA reductases via charge-charge interaction with the active site histidine. To first verify the sequence-based inference that His 398 is the catalytic histidine of the H. volcanii enzyme, enzyme H398Q was constructed, purified, and assayed for catalysis of three reactions: [1] reductive deacylation of HMG-CoA, [2] reduction of mevaldehyde, and [3] oxidative acylation of mevaldehyde. Enzyme H398Q had low activity for catalysis of reaction [1] or [3], but readily catalyzed mevaldehyde reduction. By analogy to hamster HMG-CoA reductase, we conclude that His 398 is the active site histidine. Mutant forms of the 403-residue H. volcanii enzyme were constructed to model phosphorylation and infer whether attenuated activity involved interaction with His 398. Chimeric H. volcanii-hamster enzymes constructed in an effort to create an active, phosphorylatable chimeric enzyme were inactive or not phosphorylated. We therefore added Asp at position 404 to mimic the introduction of negative charge that would accompany phosphorylation. Enzyme 404D/H398Q was inactive for reaction [1] or [3], but catalyzed reaction [2] at 35% the wild-type rate. These observations are consistent with the model that attenuation of catalytic activity results from an ionic interaction between the imidazolium cation of His 398 and the carboxylate anion of Asp 404.

Prior work from this laboratory characterized eukaryotic (hamster) and eubacterial (Pseudomonas mevalonii) 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductases. We report here the characterization of an HMG-CoA reductase from the third domain, the archaea. HMG-CoA reductase of the halobacterium Haloferax volcanii was initially partially purified from extracts of H. volcanii. Subsequently, a portion of the H. volcanii lovastatin (formerly called mevinolin) resistance marker mev was subcloned into the Escherichia coli expression vector pT7-7. While no HMG-CoA reductase activity was detectable following expression in E. coli, activity could be recovered after extracts were exposed to 3 M KCl. Following purification to electrophoretic homogeneity, the specific activity of the expressed enzyme, 24 microU/mg, equaled that of homogeneous hamster or P. mevalonii HMG-CoA reductase. Activity was optimal at pH 7.3. Kms were 66 microM (NADPH) and 60 microM [(S)-HMG-CoA]. (R)-HMG-CoA and lovastatin inhibited competitively with (S)-HMG-CoA. H. volcanii HMG-CoA reductase also catalyzed the reduction of mevaldehyde [optimal activity at pH 6.0; Vmax 11 microU/mg; Kms 32 microM (NADPH), 550 microM [(R,S)-mevaldehyde]] and the oxidative acylation of mevaldehyde [optimal activity at pH 8.0; Vmax 2.1 microU/mg; Kms 350 microM (NADP+), 300 microM (CoA), 470 microM [(R,S)-mevaldehyde]]. These properties are comparable to those of hamster and P. mevalonii HMG-CoA reductases, suggesting a similar catalytic mechanism.