Environmental sources and transmission of Escherichia coli O157 in feedlot cattle.

A study was conducted in 2 feedlots in southern Alberta to identify environmental sources and management factors associated with the prevalence and transmission of Escherichia coli O157:H7. Escherichia coli O157:H7 was isolated in preslaughter pens of cattle from feces (0.8%), feedbunks (1.7%), water troughs (12%), and incoming water supplies (4.5%), but not from fresh total mixed rations. Fresh total mixed rations did not support the growth of E. coli O157:H7 and E. coli from bovine feces following experimental inoculation. Within a feedlot, the feces, water troughs, and feedbunks shared a few indistinguishable subtypes of E. coli O157:H7. A few subtypes were repeatedly isolated in the same feedlot, and the 2 feedlots shared a few indistinguishable subtypes. The prevalence of E. coli O157:H7 in water troughs of preslaughter cattle in 1 feedlot was associated with season, maximum climatic temperatures the week before sampling; total precipitation the week before sampling, and coliform and E. coli counts in the water trough.

Identification of a mutant bovine herpesvirus-1 (BHV-1) in post-arrival outbreaks of IBR in feedlot calves and protection with conventional vaccination.

Outbreaks of infectious bovine rhinotracheitis (IBR) have recently been observed in vaccinated feedlot calves in Alberta a few months post-arrival. To investigate the cause of these outbreaks, lung and tracheal tissues were collected from calves that died of IBR during a post-arrival outbreak of disease. Bovine herpesvirus-1 (BHV-1), the causative agent of IBR, was isolated from 6 out of 15 tissues. Of these 6 isolates, 5 failed to react with a monoclonal antibody specific for one of the epitopes on glycoprotein D, one of the most important antigens of BHV-1. The ability of one of these mutant BHV-1 isolates to cause disease in calves vaccinated with a modified-live IBR vaccine was assessed in an experimental challenge study. After one vaccination, the majority of the calves developed humoral and cellular immune responses. Secondary vaccination resulted in a substantially enhanced level of immunity in all animals. Three months after the second vaccination, calves were either challenged with one of the mutant isolates or with a conventional challenge strain of BHV-1. Regardless of the type of virus used for challenge, vaccinated calves experienced significantly (P < 0.05) less weight loss and temperature rises, had lower nasal scores, and shed less virus than non-vaccinated animals. The only statistically significant (P < 0.05) difference between the 2 challenge viruses was the amount of virus shed, which was higher in non-vaccinated calves challenged with the mutant virus than in those challenged with the conventional virus. These data show that calves vaccinated with a modified-live IBR vaccine are protected from challenge with either the mutant or the conventional virus.

Canadian beef quality audit 1998-99.

The second beef quality audit was conducted in Canada in 1998-99 to determine the prevalence of quality defects in slaughtered cattle and to monitor changes since the first audit in 1995. Approximately 0.6% of the number of cattle processed annually in Canada were evaluated. Brands were observed on 49% and tag was observed on 43% of the hides. Both brands and tag had increased from 1995. Seventy percent of the cattle were polled and 5% had full horns; thus, the number of horned cattle had decreased from 1995. Bruises were found on 54% of the carcasses, which was a decrease from 78% in 1995. Sixty-eight percent of the bruises were minor, 28% major, and 4% critical in severity. The distribution of bruises on the carcass was 17% on the chuck, 36% on the rib, 30% on the loin, and 16% on the round. Grubs were observed on 0.008% of the carcasses, and surface injection site lesions were observed on 0.2% of the whole carcasses, a decrease from the 1.3% seen in 1995. Seventy-two percent of the livers were passed for human food and 14% for pet food; 14% were condemned. Approximately 64% of the liver losses were due to abscesses. Five percent of the heads and tongues and 0.3% of the whole carcasses were condemned. The hot carcass weight was highly variable in all cattle, averaging 353 kg (s = 43). The average ribeye area was 90 cm2 (s = 13). Both hot carcass weight and ribeye area had increased from 1995. The average grade fat was 9 mm (s = 5), ranging from 0 mm to 48 mm. Lean meat yield averaged 58.8% (s = 4.6). One percent of the carcasses were devoid of marbling, 17% were Canada A, 49% were Canada AA, 32% were Canada AAA, and 1% were Canada Prime, which was an increase in marbling from 1995. Dark cutters were found in 1% of all carcasses; 1% of steers, 0.5% of heifers, 3% of cows, and 14% of bulls. Three percent of the carcasses were underfinished and 13% were overfinished. The number of overfinished carcasses had increased from 1995. Stages, steers with bullish traits, were infrequently observed in 0.5% of the steers, and 0.2% of the steers and 0.3% of the heifers had poor conformation. Yellow fat was not observed in any steers or heifers, but it was found on 65% of the cow carcasses. Only 0.6% of the heifers had an aged carcass, based on skeletal maturity. Based on August 1998 to July 1999 prices, it was estimated that the Canadian beef industry lost $82.62 per head processed, or $274 million annually, from quality nonconformities, which was an increase from 1995. Additional improvements in management, feeding, handling, genetics, marketing, and grading are needed in the beef industry to reduce quality defects.

The effect of animal health products on the formation of injection site lesions in subprimals of experimentally injected beef calves.

Two hundred and twenty beef calves were used in an experimental study to determine the occurrence of injection site lesions at slaughter (15 to 18 months of age) following subcutaneous and intramuscular injection of various products into the top hip (top butt), thigh (round), and neck or rib of calves at birth, branding, or weaning. Products tested were: 2 different preparations of selenium; a 2-way, a 7-way, and an 8-way clostridial bacterin; 2 combination 7-way clostridial and Haemophilus somnus bacterins; 2 H. somnus bacterins; 2 different 4-way modified-live viral respiratory vaccines; a 4-way killed viral and H. somnus vaccine; and penicillin, florfenicol, ceftiofur, trimethoprim-sulfa, and tilmicosin. The occurrence of lesions, number of steaks affected with lesions, the trim weight of lesions, the histological class of lesions, and the estimated economic losses are described. Generally, products administered subcutaneously in the neck produced minimal tissue damage and economic losses.

Experimental inoculation of heifers with bovine adenovirus type 3.

Nine 2-year-old heifers having BAd3-neutralizing antibody titers between 1:120 and 1:1080 were individually exposed intranasally to an aerosol of 10(8) pfu of wild type (wt) bovine adenovirus type 3 (BAd3). Four animals were kept as non-inoculated controls. The heifers were examined daily for rectal temperature, weight gain/loss, nasal and ocular discharges, and other clinical signs for 10 d post-inoculation. None of the animals showed any sign of clinical disease. Virus excretion was observed in one animal only on Day 3 post-inoculation. All BAd3-inoculated heifers demonstrated a significant (P < 0.005, paired t-test) rise in BAd3-specific serum IgG, IgG1, or IgG2 ELISA titers and virus-neutralizing antibody titers compared to the titers before inoculation. All virus-inoculated animals demonstrated increased levels of BAd3-specific IgA ELISA titers in nasal secretions. These results suggest that in the presence of circulating BAd3-neutralizing antibodies, intranasal inoculation of cattle with wt BAd3 would result in inapparent infection.

The prevalence of verotoxins, Escherichia coli O157:H7, and Salmonella in the feces and rumen of cattle at processing.

Fecal samples collected from cattle at processing during a 1-year period were tested for verotoxins (VT1, VT2), Escherichia coli O157:H7, and Salmonella. Verotoxins were detected in 42.6% (95% CI, 39.8% to 45.4%), E. coli O157:H7 in 7.5% (95% CI, 6.1% to 9.1%), and Salmonella in 0.08% (95% CI, 0.004% to 0.5%) of the fecal samples. In yearling cattle, the median within-lot prevalence (percentage of positive samples within a lot) was 40% (range, 0% to 100%) for verotoxins and 0% for E. coli O157:H7 (range, 0% to 100%) and Salmonella (range, 0% to 17%). One or more fecal samples were positive for verotoxins in 80.4% (95% CI, 72.8% to 86.4%) of the lots of yearling cattle, whereas E. coli O157:H7 were detected in 33.6% (95% CI, 26.0% to 42.0%) of the lots. In cull cows, the median within-lot prevalence was 50% (range, 0% to 100%) for verotoxins and 0% (range, 0% to 100%) for E. coli O157:H7 and Salmonella (range, 0% to 0%). Verotoxins were detected in one or more fecal samples from 78.0% (95% CI, 70.4% to 84.2%) of the lots of cull cows, whereas E. coli O157:H7 were detected in only 6.0% (95% CI, 3.0% to 11.4%) of the lots of cull cows. The prevalence of verotoxins in fecal samples was lower in yearling cattle than in cull cows, whereas the prevalence of E. coli O157:H7 in fecal samples was higher in yearling cattle than in cull cows. The prevalence of E. coli O157:H7 in fecal samples was highest in the summer months. Rumen fill, body condition score, sex, type of cattle (dairy, beef), and distance travelled to the plant were not associated with the fecal prevalence of verotoxins or E. coli O157:H7. The prevalence of verotoxins in fecal samples of cull cows was associated with the source of the cattle. It was highest in cows from the auction market (52%) and farm/ranch (47%) and lowest in cows from the feedlot (31%). In rumen samples, the prevalence of verotoxins was 6.4% (95% CI, 4.2% to 9.4%), and it was 0.8% (95% CI, 0.2% to 2.3%) for E. coli O157:H7, and 0.3% (95% CI, 0.007% to 1.5%) for Salmonella.

The effect of vaccines and antimicrobials on the formation of injection site lesions in subprimals of experimentally injected beef calves.

Two hundred and thirty-nine beef calves were used to determine the occurrence of injection site lesions at slaughter (16 to 17 mo of age) following the use of 3 different 8-way clostridial bacterins, a 4-way viral respiratory vaccine, various long-acting oxytetracycline preparations, florfenicol, ceftiofur, and trimethoprim-sulfa when injected in the top hip (top butt), thigh (round), or neck (blade) of calves at 2 to 3 or 5 to 7 mo of age. The occurrence of lesions varied by product, route of administration, and location of injection. The number of steaks affected with lesions, the trim weight of lesions, the histological class of lesions, and the economic losses from trim are described.

Monitoring injection site lesions in Canadian yearling cattle and cull cows and bulls: Spring 1998.

Injection site lesions were found in 15% top butts, 22% blades, 6% eyes of rounds, 0.4% inside rounds, and 8% outside rounds from yearling cattle, estimated to cost $7.15/head processed ($15 million annually). In cull cows and bulls, lesions were found in 33% outside rounds, estimated to cost $3.56/head processed ($2.3 million annually).

The effect of administering long-acting oxytetracycline and tilmicosin either by dart gun or by hand on injection site lesions and drug residues in beef cattle.

Forty yearling cattle were injected intramuscularly with long-acting oxytetracycline and subcutaneously with tilmicosin by dart gun or by hand in a chute 28 days prior to slaughter. The drugs caused injection site lesions and antibiotic residues in the neck and thigh that varied by technique, dose, and site.

Injection site surveys in Canadian yearling cattle and cull cows and bulls: fall 1997.

In subprimals from yearling cattle, lesions were found in 16% top butts, 23% blades, 6% eye of rounds, 3% inside rounds, and 8% outside rounds, costing $ 9.58/head processed ($21 million annually). In cull cows and bulls, lesions were found in 35% outside rounds, costing $6.34/head processed ($4.1 million annually).

Injection site survey in Canadian-fed cattle: spring 1997.

A 2nd injection site survey was conducted during the spring of 1997 in Canadian-fed beef. The prevalence of lesions was 13.3% in top butts, 23.1% in blades, 9.1% in eye of rounds, 7.5% in outside rounds, and 1.4% in inside rounds. Losses were $8.05/head processed or $17 million annually.

Canadian beef quality audit.

A study was conducted in 4 Canadian processing plants in 1995-96 to determine the prevalence of quality defects in Canadian cattle. One percent of the annual number of cattle processed in Canada were evaluated on the processing floor and 0.1% were graded in the cooler. Brands were observed on 37% and multiple brands on 6% of the cattle. Forty percent of the cattle had horns, 20% of which were scurs, 33% were stubs, 10% were tipped, and 37% were full length. Tag (mud and manure on the hide) was observed on 34% of the cattle. Bruises were found on 78% of the carcasses, 81% of which were minor in severity. Fifteen percent of the bruises were located on the round, 29% on the loin, 40% on the rib, 16% on the chuck, and 0.02% on the brisket. Grubs were observed in 0.02% of the steers, and injection sites were observed in 1.3% of whole hanging carcasses. Seventy percent of the livers were passed for human food and 14% for pet food; 16% were condemned. Approximately 71% of the liver condemnations were due to liver abscesses. Four percent of the heads, 6% of the tongues, and 0.2% of whole carcasses were condemned. The pregnancy rate in female cattle was approximately 6.7%. The average hot carcass weight was 357 kg (s = 40) in steers, 325 kg (s = 41) in heifers, 305 kg (s = 53) in cows, 388 kg (s = 62) in virgin bulls and 340 kg (s = 39) in mature bulls. The average ribeye area in all cattle was 84 cm2 (s = 12); range 29 cm2 to 128 cm2. Grade fat was highly variable and averaged 9 mm (s = 4) for steers and heifers, 6 mm (s = 6) for cows, 5 mm (s = 1) for virgin bulls, and 4 mm (s = 0.5) for mature bulls. The average lean meat yield was 59.7% in cattle (s = 3.4); range 39% to 67%. One percent of the carcasses were devoid of marbling, 1% were dark cutters, and 0.05% of the steer carcasses were staggy. Six percent of the carcasses had poor conformation, 3.7% were underfinished, and 0.7% were overfinished. Yellow fat was observed in 4% of the carcasses; 10% of carcasses were aged. Based on January 1996 prices, the economic analysis showed that the Canadian beef industry lost $70.52 per head or $189.6 million annually from quality nonconformities. Methods identified to reduce these nonconformities included improvements in management, animal identification, handling, genetic selection, marketing, grading, and information transfer.

Protective immunity in cattle following vaccination with conventional and marker bovine herpesvirus-1 (BHV1) vaccines.

The efficacy of two experimental subunit gD vaccines and two commercial whole virus vaccines was determined in a bovine herpesvirus-1 (BHV1) challenge trial. Full-length gD and a truncated, secreted form of gD (tgD) were produced using a vaccinia virus expression system and purified by affinity chromatography. Comparison of these forms of gD did not reveal significant structural or antigenic differences. Calves immunized with gD or tgD in avridine developed significantly (P < 0.05) higher neutralizing antibody titers in the serum and nasal mucosa than animals vaccinated with killed virus (KV) or modified live virus (MLV). Following challenge with BHV1, all vaccinated calves had significantly (P < 0.05) lower rectal temperatures and clinical scores than those in the placebo group. In contrast to the KV-, MLV- and placebo-vaccinated calves, the gD and tgD-immunized animals experienced minimal weight loss and virus shedding post-challenge. Glycoprotein B-specific antibodies were detected in KV- and MLV-vaccinated calves, but not in gD- or tgD-immunized animals. These data suggest that full-length or truncated gD, when formulated in an appropriate adjuvant, is more effective than two KV and MLV vaccines and may be used as a marker vaccine for concurrent vaccination and eradication programs of BHV1.

Losses over a 2-year period associated with fetal infection with the bovine viral diarrhea virus in a beef cow-calf herd in Saskatchewan.

In 1992, significant calf losses occurred between birth and weaning in a 650-cow Saskatchewan beef herd. These losses occurred subsequent to ill-thrift and disease, and every calf necropsied was found to be persistently infected with bovine viral diarrhea virus (BVDV). The objectives of this study were to describe the losses associated with fetal infection with BVDV in this herd and to determine why they occurred. For investigative purposes, blood samples were collected from the entire cow herd and the surviving calves at pregnancy testing in 1992, and tested by virus isolation for BVDV. Between 51 and 71 persistently infected calves were born in 1992. Bovine viral diarrhea virus was only isolated from calves. The only confirmed fetal infections with BVDV were recorded as the birth of persistently infected calves. However, abortions, reduced pregnancy rates, and delayed calvings were also recorded in the cow herd and may have been the result of fetal infections. The herd was monitored again in 1993. Fetal infections with BVDV were recorded as the birth of stunted, deformed, and persistently infected calves. The greatest losses due to fetal infection with BVDV in the 2 years of this study occurred in cows that were 3-years-old at calving (second calves). Bovine viral diarrhea virus appears to have remained endemic in this herd by transmission from persistently infected calves on young 3- and 4-year-old cows to naive calved 2-year-old cows that were mingled with them annually for rebreeding. Significant numbers of the 2-year-old cows remained naive to BVDV, because they were segregated from persistently infected calves at weaning, preventing cross-infection with BVDV.

A survey of injection site lesions in fed cattle in Canada.

During November 1996 to January 1997, a survey was conducted at 5 Canadian purveyors to measure the prevalence of injection site lesions in the top butt, boneless blade, outside round, inside round, and eye of the round. As trimmers were cutting these subprimals into steaks, technicians monitored each steak for grossly obvious scars. These scars were trimmed, weighed, and scored as either a "clear scar," "woody callus," or "cyst." All scars were subsequently examined histologically and classified as a "clear scar," "woody callus," "scar with nodules," "mineralized scar," or "cyst." Pieces were observed for broken needles while being processed and none were found. The estimated prevalence of injection site lesions was 18.8% (95% CI, 16.4% to 21.2%) in top butts, 22.2% (95% CI, 18.8% to 25.7%) in boneless blades, 4.9% (95% CI, 3.6% to 6.3%) in the eye of round, 1.8% (95% CI, 1.1% to 2.9%) in the inside round, and 7.6% (95% CI, 5.6% to 9.8%) in the outside round. Some top butts originated from American fed cattle; the estimated prevalence of lesions was 9.0% (95% CI, 5.9% to 12.9%) in American top butts and 22.3% (95% CI, 19.4% to 25.3%) in Canadian top butts. The median weight of the lesions varied among subprimals and ranged from 64 g to 117 g. Histologically, 13% of the scars were clear scars, 47% were woody calluses, 5% were mineralized scars, 34% were scars with nodules, 0.2% were cysts, and 0.9% were normal fat infiltrations. An economic analysis estimated an average loss of $8.95 per fed animal processed or $19 million dollars annually to the Canadian beef industry from injection scars.

Efficacy of an experimental BHV-1 subunit gIV vaccine in beef calves challenged with BHV-1 in aerosol.

Thirty-six beef calves were used to test the efficacy of an experimental truncated BHV-1 glycoprotein (tgIV) vaccine. Calves from 1 source and +/- 1 mo of age were randomly divided into 4 groups: 1) control (adjuvant VSA3), 2) vaccinated with tgIV at 3 and 4 mo of age, 3) vaccinated with tgIV at 3 and 7 mo of age, or 4) vaccinated with tgIV at 6 and 7 mo of age. Calves were challenged with BHV-1 in aerosol (strain 108) at 7 1/2 mo of age. Prior to challenge, serum neutralizing (SN) antibody titers to BHV-1 were significantly (P < 0.05) higher in all vaccinated calves than in controls. Calves vaccinated at 3 and 7, or 6 and 7, mo of age had significantly (P < 0.05) higher SN antibody and nasal antibody titers to BHV-1 and ELISA (enzyme linked immunosorbent assay) titers to gIV at prechallenge than those vaccinated at 3 and 4 mo of age or controls. Postchallenge nasal shedding of BHV-1 occurred only in controls and those vaccinated at 3 and 4 mo of age. Control calves lost significantly (P < 0.05) more weight and had higher sick scores after challenge than those vaccinated at 3 and 7, or at 6 and 7, mo of age. There were strong correlations (P < 0.001) between antibody titers, virus shedding, and sickness.

Regulation of bovine acute phase responses by recombinant interleukin-1 beta.

The acute phase response is a collection of physiologic changes initiated early in the inflammatory process. This response is comprised of both localized changes at the site of infection or injury and the initiation of systemic responses, such as the increase in production of acute phase proteins. Cytokines such as interleukin (IL)-1, IL-6, and tumor necrosis factor (TNF) play key roles in the regulation of acute phase response in the species studied to date. To better characterize the acute phase response of cattle, recombinant bovine (rBo). IL-1 beta was administered to cattle. A single administration of rBoIL-1 beta was able to induce a dose dependent increase in body temperature, circulating leukocytes, and serum haptoglobin and fibrinogen concentrations, as well as a decrease in plasma zinc concentration. Five daily administrations of rBoIL-1 beta resulted in heightened and prolonged elevations of haptoglobin and fibrinogen. In addition, alpha 1-acid glycoprotein levels were increased, a response not seen after a single administration of rBoIL-1 beta. These results indicate that IL-1 is an important regulator of the acute phase response in cattle.

Effects of various vaccination protocols on passive and active immunity to Pasteurella haemolytica and Haemophilus somnus in beef calves.

Two field trials were conducted in a beef cow herd in Saskatchewan to determine the effectiveness of a combined Pasteurella haemolytica and Haemophilus somnus vaccine in increasing passively and actively acquired antibodies in beef calves. Vaccination of dams at 4 and/or 7 weeks prepartum was associated with increased antibody titers to P. haemolytica and H. somnus in their serum (P < 0.05), colostrum(P < 0.05), and serum of their calves at 3 days and 1 month of age (P < 0.05). There was no significant(P > 0.05) difference in antibody titers in the colostrum and serum of calves from single or double vaccinated dams. Calves vaccinated at 1 and 2 months of age in the face of maternal antibodies toP. haemolytica and H. somnus had significantly(P < 0.05) higher antibodies to P. haemolytica and H. somnus at 4 and 6 months of age than did unvaccinated calves. Calves vaccinated at 3 and 4 months of age in the face of low levels of preexisting antibodies had significantly (P < 0.05) higher antibodies toP. haemolytica at 5 months of age and to H. somnus at 5 and 6 months of age than did unvaccinated calves. Calves vaccinated once at 4 months of age had significantly(P < 0.05) higher antibody titers toP. haemolytica and H. somnus at 4.5 months of age than did unvaccinated calves, but this difference was not apparent at 6 months of age. These results suggest that vaccination of beef cows with a combined Pasteurella haemolytica and Haemophilus somnus vaccine once at 4 weeks prepartum will significantly (P < 0.05) increase passive antibody titers toP. haemolytica and H. somnus in their calves. Double vaccination of calves with preexisting maternal antibodies at 1 and 2 months of age will increase antibody titers to P. haemolytica and H. somnus until 6 months of age. Vaccination of beef calves with low levels of preexisting antibody at 3 and 4 months of age will increase antibody titers to H. somnus until 6 months of age and to P. haemolytica until 5 months of age.However, the level of antibodies achieved by vaccination may depend on the calves being studied, the level of preexisting antibodies, and the efficiency of passive transfer.