Chickens in a low-stress environment (heterophil/lymphocyte ratio 0.31) were given feed containing 30, 40, or 60 mg of corticosterone/kg of feed for 0.5 hour. Between 0.5 to 12 hours later, chickens were exposed to Escherichia coli via the air sac route. For each dose of corticosterone, there was an untreated control group that was exposed to E coli via the air sac route. The prevalence of pericarditis was reduced from 78 to 7% between 2 and 4 hours after exposure. Resistance was associated with heterophil/lymphocyte (H/L) ratios greater than 1.04. Peak H/L ratios correlated positively with amount of corticosterone in the feed. In one experiment, chickens were inoculated IV with sheep erythrocytes at various times after consumption of feed containing corticosterone. Suppression of antibody responsiveness was most pronounced 4 hours later. Antibody responsiveness correlated positively with lymphocyte numbers. Histologic examination of air sacs was made following euthanasia at various times after E coli exposure. Lesions observed in control chickens included: edema at 0.5 hour, beginning of heterophil infiltration at 1 hour, increased edema and heterophil infiltration at 2 hours, and severe edema and heterophil infiltration at 4 hours. Lesions were not observed in chickens that had been given feed containing 40 mg of corticosterone/kg of feed.

An experimental model for subclinical edema disease was developed in weanling pigs. In multiple experiments, 3-week-old pigs were weaned, then inoculated intragastrically with 10(10) colony-forming units of an SLT-IIv-positive strain of Escherichia coli originally isolated from a pig with edema disease (principals). Control pigs were inoculated with a nonpathogenic E coli strain. Of 39 principals, 8 developed clinical edema disease within 14 days after inoculation. However, 20 of 21 principals that did not develop clinical signs of edema disease, but were submitted for necropsy examination at 14 days after inoculation, had characteristic vascular lesions of edema disease. Vascular lesions, found principally in ileum and brain, consisted of segmental necrosis of myocytes in the tunica media of small arteries and arterioles. None of the pigs inoculated with a nonpathogenic strain of E coli developed edema disease or vascular lesions. None of the principals necropsied at 2 days after inoculation had vascular lesions. Development of vascular lesions by 14 days after inoculation was used as the end point for detecting subclinical edema disease in the model.

Development of age-dependent resistance to enterotoxigenic Escherichia coli was studied, using isolated enterocytes and brush border membranes (BBM) from 7-day-old and 7-week-old pigs. Binding of 125I-labeled heat-stable (125I-STa) enterotoxin to enterocytes and BBM was specific, temperature- and time-dependent, saturable, and partially reversible. Scatchard analysis revealed a single class of receptors. Mean +/- SD avidity of binding (apparent affinity constant, Ka) of 125I-STa to enterocytes from 7-day-old and 7-week-old pigs was 2.14 +/- 0.29 X 10(8) and 2.72 +/- 0.25 X 10(8) L/mol, respectively. Numbers of STa receptors were calcuated to be 64,903 +/- 2,900/enterocyte for 7-day-old pigs and 53,029 +/- 3,117/enterocyte for 7-week-old pigs. Numbers of STa receptors expressed per milligram of BBM protein from 7-day-old pigs were 2.66 X 10(11), compared with 2.29 X 10(11) for BBM from 7-week-old pigs. By 5 minutes after addition of STa to reaction mixtures, intracellular cyclic guanosine monophosphate concentration increased 13.9-fold in enterocytes from 7-day-old pigs and 8.7-fold in enterocytes from 7-week-old pigs. The particulate guanylate cyclase activity associated with BBM from 7-week-old pigs was slightly more sensitive to low amounts of STa, compared with BBM from 7-day-old pigs; however, differences were not observed at intermediate and high amounts. These data indicate that lack of a secretory response to STa by older pigs is not attributable either to decreased numbers of STa receptors or to decreased signal response between the STa receptor and membrane-bound guanylate cyclase. Development of age-dependent resistance by porcine small intestine to STa appears to be attributable to steps in the secretory pathway that respond to increased concentration of cyclic guanosine monophosphate.

A study was performed to determine whether equine peritoneal macrophages produce interleukin 6 (IL-6) in vitro in response to endotoxin. Peritoneal fluid was collected from 14 clinically normal adult horses and was used as the source of peritoneal macrophages. Macrophages from each horse were isolated and cultured separately in vitro in the absence or presence of various concentrations (0.5, 5, or 500 ng/ml) of endotoxin (lipopolysaccharide from Escherichia coli 055:B5). Culture medium supernatants were collected after 3, 6, 12, and 24 hours' incubation and were frozen at - 70 C until assayed for IL-6 activity. Supernatant IL-6 activity was determined by use of a modified colorimetric assay and the murine hybridoma cell line B13.29 clone B.9, which is dependent on IL-6 for survival. Results indicated that equine peritoneal macrophages produce IL-6 in vitro and that supernatant medium IL-6 activity was significantly (P < 0.05) increased by exposure to endotoxin. Significant (P < 0.05) time and treatment effects on macrophage IL-6 production were apparent. The IL-6 activity peaked at 6 or 12 hours' incubation, then remained high through 24 hours' incubation, regardless of endotoxin exposure. Medium IL-6 activity during 3 and 6 hours' incubation was significantly (P < 0.05) greater in macrophages exposed to 5 or 500 ng of endotoxin/ml than in those exposed to 0.5 ng of endotoxin/ml; however peak IL-6 activity was similar among all endotoxin concentrations. Endotoxin concentration did not have an effect on medium IL-6 activity from macrophages exposed to endotoxin for 12 or 24 hours.

Three-week-old weaned and colostrum-deprived neonatal (< 1 day old) pigs were inoculated to determine the pathogenicity of 2 enterotoxigenic Escherichia coli isolates that do not express K88, K99, F41, or 987P adhesins (strains 2134 and 2171). Strains 2134 and 2171 were isolated from pigs that had diarrhea after weaning attributable to enterotoxigenic E coli infection. We found that both strains of E coli adhered in the ileum and caused diarrhea in pigs of both age groups. In control experiments, adherent bacteria were not seen in the ileum of pigs < 1 day old or 3 weeks old that were noninoculated or inoculated with a nonpathogenic strain of E coli. These control pigs did not develop diarrhea. Antisera raised against strains 2134 and 2171 and absorbed with the autologous strain, grown at 18 C, were used for bacterial-agglutination and colony-immunoblot assays. Both absorbed antisera reacted with strains 2134 and 2171, but not with strains that express K99, F41, or 987P adhesins. A cross-reaction was observed with 2 wild-type K88 strains, but not with a K12 strain that expresses K88 pili. Indirect immunofluorescence with these absorbed antisera revealed adherent bacteria in frozen sections of ileum from pigs infected with either strain. We concluded that these strains are pathogenic and express a common surface antigen that may be a novel adhesin in E coli strains that cause diarrhea in weaned pigs.

The protective effects of egg yolk powder prepared from hens vaccinated with heat-extracted antigens from K99-piliated enterotoxigenic Escherichia Coli (ETEC) strain 431 were evaluated in a colostrum-fed calf model of ETEC-induced diarrhea caused by a heterologous strain (B44). The antibody powder was obtained by spray-drying the water-soluble protein fraction of egg yolks after removing the lipid and fatty components by precipitation with hydroxypropylmethylcellulose phthalate. A total of 16 colostrum-fed calves were studied to determine whether the orally administered antibody powder would prevent fatal bovine colibacillosis caused by a virulent ETEC strain. Clinical response of individual calves was monitored and evaluated in the context of these variables: fecal consistency score, intestinal colonization, weight loss, and mortality. Control calves that were treated with vehicle (milk with egg yolk powder from nonimmunized hens) had severe diarrhea and dehydration and died within 72 hours after infection was manifested. In contrast, calves fed milk containing egg yolk powder with antipili agglutinin titers of 1:800 and 1:1,600 had transient diarrhea, 100% survival, and good body weight gain during the course of the study. Results indicate that the orally administered egg yolk powder protected against ETEC-induced diarrhea in neonatal calves and that the protective components may have been the antibodies raised by vaccination of chickens against ETEC.

In 8 Holstein cows, 50 colony-forming units (CFU) Of Escherichia coli was administered into 1 mammary gland. Infections were established in all inoculated glands. In 4 of the 8 cows, 500 mg of gentamicin sulfate was administered by intramammary infusion 14 hours after inoculation; the other 4 cows were untreated controls. Infusions of gentamicin also were given after each of the 3 successive milkings after the initial infusion, so that a total dose of 2 g of gentamicin was given to each of the treated cows. During the 33-hour treatment period and for the first milking after the last infusion of gentamicin, the treated cows had a mean gentamicin concentration of greater than or equal to 31.0 microgram/ml in milk samples that were collected from inoculated quarters immediately before each milking. Concentrations of 0.34 and 0.69 microgram of gentamicin were detected in milk from 2 cows at 8 days after inoculation with E coli. Mean serum concentrations of gentamicin were > 0.37 microgram/ml throughout the treatment period and the first 12 hours after the last infusion, with a mean peak concentration of 0.96 microgram/ml at 24.4 hours. The range of peak concentration of gentamicin detected in urine from all treated cows was 42 to 74.4 microgram/ml. Peak concentration of E coli in milk in the treated cows (6.08 +/- 1.02 log10 CFU/ml) did not significantly (P > 0.05) differ from that of the control cows (5.26 +/- 1.00 log10 CFU/ml). Similarly, mean duration of infection in the treated cows (54 hours) did not differ significantly from that of the control cows (48 hours). The treatment groups also did not differ significantly in peak concentrations of albumin or IgG1 in milk, although mean concentrations of albumin and IgG1 at 16 hours after inoculation, and of albumin at 20 hours, was significantly (P < 0.05) higher in the milk from control cows than from the treated cows. Mean values of peak rectal temperature and of mean rectal temperature throughout the trial did not differ between the groups. At the end of the 4-week trial, 1 of 4 inoculated glands in treated cows and 3 of 4 in control cows had somatic cell counts less than or equal to preinoculation concentrations (5.18 log10 cells/ml). Intramammary administration of gentamicin did not affect the duration or severity of experimentally induced E coli mastitis. In addition, substantial concentrations of gentamicin were detected in the serum of treated cows, suggesting that intramammary treatment may result in prolonged drug residues in tissue.

Electrodes were surgically implanted at 15-cm intervals in the jejunum and ileum of 4 healthy neonatal calves so that myoelectric activity could be recorded on 2 consecutive days. On the first day, each calf received a control treatment, and myoelectric activity was recorded for 340 minutes. Phase I was recorded for a mean of 175.8 +/- 22.8 minutes (51.5%), phase II for 124 +/- 27.4 minutes (36.5%), and phase III for 40.3 +/- 6 minutes (11.9%). On the second day, each calf was treated with approximately 200 micrograms of heat-stable enterotoxin (STa) of Escherichia coli orally. All calves developed diarrhea after the administration of STa. Phase I was recorded for a mean of 92.5 +/- 42.3 minutes (27.2%), phase II for 227.3 +/- 52.5 minutes 66.9%), and phase III for 20.3 +/- 11.4 minutes (6.0%). Increase in phase II and decrease in phases I and III after STa administration were significant (P < 0.05). Duration of the migrating myoelectric complex was longer after STa administration (median, 64 minutes), compared with the control treatment (median, 54 minutes). Minute rhythms, recorded on the day of toxin administration, ranged from 49 to 153 minutes. There was no difference between the number of migrating action potential complexes on the control days (range, 1 to 10), compared with those on treatment days (range, 1 to 14). These findings are suggestive that enterotoxin-induced diarrhea of calves is accompanied by increased total spiking activity and minute rhythms in the distal portion of the jejunum and ileum.

Because hepatocyte-stimulating factor/interleukin 6 (IL-6) the principal inducer of acute-phase protein synthesis in the liver, quantification of its activity in blood provides an early and sensitive assessment of the acute-phase response. Circulating IL-6 activity was monitored in 4 adult horses for 72 hours after IV administration of endotoxin. In 4 experiments performed at weekly intervals and in randomized order, each horse was given endotoxin-1,000, 30, 1, and 0 ng/kg of body weight. Plasma IL-6 activity was quantified as the ability to promote growth of the IL-6-dependent B-cell hybridoma, B13.29 clone B9. Interleukin-6 activity (171 +/- 10.2 U/ml) was found in all pretreatment plasma samples and was significantly (P < 0.05) increased above baseline from 2 to 12 hours after 1,000 ng of endotoxin/kg was given and at 3 hours after 30 ng of endotoxin/kg was given. After 1,000- or 30-ng/kg dosage of endotoxin, peak plasma IL-6 activity (10,128 +/- 4,096 and 1,555 +/- 1,326 U/ml, respectively) was observed for 3 hours. The IL-6 response of endotoxin-treated horses began about 1 hour after tumor necrosis factor appeared in the circulation, and its course closely approximated the endotoxin-induced febrile reaction. Significant increase in plasma IL-6 activity was not detected in horses given 1 ng of endotoxin/kg or control buffer.