Efficacy of parenteral antibiotics for disease prophylaxis in feedlot calves

Trimethoprim-sulfadoxine (TMPSDX) and two formulations of oxytetracycline (OTC) were examined for their prophylactic efficacy in feedlot calves when given by intramuscular injection on arrival at a large commercial feedlot. The study included 2,112 high-risk feeder calves that developed disease early in the feeding period. Both formulations of OTC reduced bovine respiratory disease morbidity during the first two weeks on feed and for the entire feeding period by 15-19% (p<0.05), and they also reduced all fatal fibrinous pneumonia by 67% and 84% (p<0.05). All three drugs significantly reduced all fatal disease in animals first treated during the second week on feed, but not for the overall feeding period. Oxytetracycline with 2-pyrrolidone reduced the incidence of all fatal disease by 44% (p<0.05) during the entire feeding period. The case fatality risk for calves first treated during the second week on feed was lower (p<0.05) in the TMPSDX group and in the OTC with polyvinyl-pyrrolidone group.     

Comparison of two formulations of oxytetracycline given prophylactically to reduce the incidence of bovine respiratory disease in feedlot calves

A trial involving 1,803 feedlot calves was conducted under commercial feedlot conditions in western Canada to compare the relative effectiveness of a new oxytetracycline formulation, administered either intramuscularly (BMI) or subcutaneously (BMS), to a currently available oxytetracycline formulation, administered intramuscularly (LAB), for the prevention of bovine respiratory disease (BRD) in feedlot calves. All experimental treatments were administered upon arrival at the feedlot and again on the third day after arrival.

Over the entire feeding period, there were no significant differences (p≥0.05) in the BRD treatment rates or the BRD relapse rates between either the BMI or BMS groups compared to the LAB group. Similarly, there were no significant differences (p≥0.05) in the BRD treatment rates in the BMI or BMS groups from days 8-14, days 15-90, or days 1-90 of the feeding period compared to the LAB group. However, during the first seven days of the feeding period the BRD treatment rate in the BMI group was 1.55 times (p<0.05) higher than in the LAB group. From days 1-90 and day 1 to the end of the feeding period, the overall mortality rates, BRD mortality rates, and BRD case fatality rates were two to six times lower in the BMS and BMI groups as compared to the LAB group; however, these differences were not statistically significant (p≥0.05).

These data indicate that both the intramuscular and subcutaneous administration of a new oxytetracycline formulation are comparable to the intramuscular administration of a currently available oxytetracycline formulation when given to calves upon arrival at the feedlot.

     

The relationship between the occurrence of undifferentiated bovine respiratory disease and titer changes to bovine coronavirus and bovine viral diarrhea virus in 3 Ontario feedlots.

Serological evidence of previous viral exposure (titer at arrival) and current viral exposure (titer increase) during a 28-day study period, was used to determine if bovine coronavirus (BCV) or bovine viral diarrhea virus (BVDV) was associated with the occurrence of undifferentiated bovine respiratory disease (UBRD) in feedlot calves. Neutralizing antibody titers to BCV and BVDV were determined for 852 animals from 3 Ontario feedlots. Calves at 2 of the 3 feedlots (n = 753) received a modified live 4-way viral vaccine containing BVDV. On arrival at the feedlots, 90% of animals were seropositive for BCV, while 39% of animals were seropositive for BVDV. This evidence of previous exposure to both viruses was associated with reduced subsequent UBRD risk. Evidence of exposure to BCV during the study period was common, as 50% of animals showed a 16-fold or greater titer increase; however, treatment for UBRD was not associated with titer change. Although the majority of animals were vaccinated for BVDV at arrival, within a feedlot, animals treated for UBRD had larger titer increases to BVDV than non-treated animals. Based on our findings we infer that BCV was not causally related to UBRD occurrence, however consistent with other literature, BVDV may be causally related to UBRD occurrence.     

The occurrence of Haemophilus somnus in feedlot calves and its control by postarrival prophylactic mass medication.

Three field trials were conducted in a large commercial feedlot in Saskatchewan to determine the prevalence of Haemophilus somnus in calves and to evaluate the efficacy of prophylactic mass medication with long-acting oxytetracycline on day 17 (1990, n = 1336), day 11 (1991, n = 4372), or day 8 (1992, n = 5632) postarrival. Hemophilosis accounted for > 40% of the mortality in feedlot calves each year. Haemophilus somnus was cultured from the blood of one febrile calf on day 1 (0.1%, n = 895), but it was not cultured from nasal swabs on day 1 or day 11 (n = 881) or from blood samples on day 11 (n = 883). Similarly, it was not cultured from nasal swabs or blood samples from sick calves first treated for bovine respiratory disease (BRD) (n = 219). Serological titers to H. somnus increased (p < 0.05) in unvaccinated calves from day 1 (Geometric mean titer = 11,846) to day 96 (Geometric mean titer = 63,712), indicating natural infection following feedlot entry. Calves that relapsed twice with BRD or died from BRD +/- hemophilosis had significantly (p < 0.06) lower titers to H. somnus on days 1 and 96 than those that did not relapse twice or die. Postarrival mass medication with long-acting oxytetracycline did not reduce (p > 0.05) the risk of hemophilosis mortality. However, it reduced (p < 0.05) the risk of BRD treatment by 14% and the risk of BRD mortality by 71%. Additional epidemiological studies of H. somnus are needed so that we can develop strategic medication and vaccination programs to reduce losses from hemophilosis.     

A comparison of trimethoprim-sulfadoxine and ceftiofur sodium for the treatment of respiratory disease in feedlot calves

A field trial was performed to compare trimethoprim-sulfadoxine to ceftiofur sodium in the treatment of bovine respiratory disease (BRD) in feedlot calves. Five-hundred-and-fifty-five recently weaned, crossbred beef calves, with naturally occurring cases of BRD, were randomly assigned to either trimethoprim-sulfadoxine or ceftiofur sodium treatment groups. The effectiveness of the antibiotics was assessed by comparing relapse rates, three day treatment response rates, mortality rates, chronicity rates, and wastage rates. There was no statistical difference in the first or second relapse rates between the two groups. For the initial therapy, first relapses, and overall treatment episodes, a significantly greater proportion of the calves treated with ceftiofur sodium responded to three days of therapy than those treated with trimethoprim-sulfadoxine (p < 0.05). This resulted in a 10% reduction in treatment costs for calves in the ceftiofur group. There were significantly lower mortality and wastage rates attributable to BRD in the ceftiofur sodium group than in the trimethoprim-sulfadoxine group (p < 0.05). However, there were no significant differences in overall mortality, overall chronicity, or overall wastage rates between the treatment groups.     

Prophylactic tilmicosin medication of feedlot calves at arrival

The parenteral administration of the antibiotic tilmicosin given on arrival at a feedlot was evaluated in a group of 304 steer calves. These calves were allotted to 24 pens so that there were 12 replicates of both the control and medicated groups. The treatment rate was reduced significantly during the first five days (p < 0.05) and during the first month (p < 0.01) of the feeding period in the medicated group. The average days from arrival until first treatment for respiratory disease was increased to 21 days in the medicated group compared to 9 days (p < 0.01) for the controls. The medicated group had improved average daily gain (p < 0.01) and feed efficiency (p < 0.01) over the trial period when compared to the nonmedicated animals.     

The effect of age at weaning on the health status of bull calves in a feedlot

Incidence of morbidity and mortality in a feedlot were compared among 381 bull calves weaned one month apart (October 3 and November 1). The calves were 156 and 192 days old at weaning in the earlier and later weaned groups, respectively. Following an adjustment period, the calves were fed a mixed finishing diet containing 90% concentrate ad lib for 140 days in a feedlot. The rate of morbidity did not differ significantly between the two weaning groups. Sick calves in the earlier weaned group had a longer treatment period than those in the later weaned group (3.2 vs 1.4 days, p<0.05). Infections of the respiratory tract were the major cause of sickness and most of the respiratory infections occurred in the early stages of the feedlot period. The frequency of respiratory infections was higher among the earlier weaned calves compared with that in the later weaned group (p<0.01) indicating a higher susceptibility to these infections when calves were weaned at younger ages. Bloat was the second most common health problem among the bulls; however, its incidence did not differ between the two groups (p>0.05). The rate of mortality did not differ significantly between the two groups.     

Associations between antimicrobial use and the prevalence of antimicrobial resistance in fecal Escherichia coli from feedlot cattle in western Canada

A randomized, controlled, blinded clinical trial was performed at a research feedlot in western Canada. Auction-market-derived steers (n = 288) were randomly assigned to 1 of 3 treatments: 1) no antimicrobials on arrival; 2) oxytetracycline in the starter ration for 14 d; and 3) long-acting oxytetracycline subcutaneously on day 0. Minimal inhibitory concentrations of 7 antimicrobials were determined for 3 generic fecal E. coli isolates per animal on arrival and throughout the feeding period. There was a low prevalence of antimicrobial resistance in generic E. coli isolates from calves on arrival. There were increased proportions of cattle with resistant E. coli isolates early in the feeding period among calves in groups 2 and 3. Individual animal treatments were not associated with increased proportions of cattle with resistant E. coli isolates preslaughter. There was no difference in the proportion of animals with E. coli isolates resistant to tetracycline between the treatment groups preslaughter. However, there were significantly more animals with tetracycline resistant isolates of E. coli preslaughter than at arrival.     

Factors associated with mortality and treatment costs in feedlot calves: the Bruce County Beef Project, years 1978, 1979, 1980.

Three years of data on factors associated with death losses and health costs in Ontario feedlot calves were analyzed. The results support the previously reported findings; however, significant differences in the third year (1980-81) of the study were noted. Calf groups that were "mixed" after arrival in the feedlot or had a larger than average number of calves (means = 142) had increased death losses and health costs. Calf groups whose ration was changed from dry hay to hay silage or corn silage as the major component of the ration during the first month after arrival had higher death losses and health costs. Feeding grain (barley/oats/corn) prior to, or concurrent with, the change to silage appeared to decrease the harmful effects. Cattle groups vaccinated against respiratory disease within two weeks of arrival experienced increased death losses and health costs. These effects were ameliorated by delaying vaccination in groups switched to silage; however, no benefits from delaying vaccination were noted in dry hay fed groups. Prophylactic antimicrobials in the water supply during the first week after arrival appeared particularly deleterious to the health of calf groups. The effects of prophylactic antimicrobials in the starter ration were unclear. During 1980-81, there was a marked decrease in the relative importance of fibrinous pneumonia as a cause of death and the feeding of silage was not significantly associated with mortality. Both these events may have arisen from the drastic decrease in the percentage of groups fed silage by two weeks postarrival (from 32% in previous years to 7% in 1980-81).     

The effect of route and dosage of immunization on the serological response to a Pasteurella haemolytica and Haemophilus somnus vaccine in feedlot calves

The effect of route and dosage of administration on the serological response to a vaccine containing genetically attenuated leukotoxin of Pasteurella haemolytica combined with bacterial extracts of P. haemolytica and Haemophilus somnus (Somnu-Star Ph, Biostar Inc., Saskatoon, Saskatchewan) was evaluated in a controlled field trial in 301 feedlot calves. Vaccination of calves on arrival at the feedlot with Somnu-Star Ph significantly (p < 0.05) increased P. haemolytica and H. somnus serum antibody titers and reduced bovine respiratory disease (BRD) morbidity. A single subcutaneous vaccination with Somnu-Star Ph was as effective in stimulating a humoral antibody response and in reducing BRD morbidity as double vaccination by the intramuscular or the subcutaneous route. Furthermore, there were no swellings or adverse reactions observed with either subcutaneous or intramuscular administration of Somnu-Star Ph.

These results suggest that feedlot calves can be immunized subcutaneously once on arrival with Somnu-Star Ph. Double vaccination was of no added value in this trial, because the majority of BRD morbidity occurred prior to revaccination fourteen days postarrival. Additional larger-sized field trials are needed to monitor the duration of immunity following vaccination and to test the effect of route and dosage of vaccination on mortality.

     

A path model of factors influencing morbidity and mortality in Ontario feedlot calves.

The principles of path analysis and causal modelling are discussed. Path analysis was applied to three data sets to assess the relationship between group characteristics (number per group and "mixing" subgroups of cattle, feeding-management of the group and processing factors (vaccination and prophylactic antimicrobials) and subsequent morbidity and mortality in feedlot cattle. The major findings agree with previously reported results but the timing and pathways of the effects are elaborated. In general, morbidity in week 1 was correlated with morbidity in week 2, which was correlated with morbidity in weeks 3-5. The same was generally true for mortality. In general, morbidity was not strongly correlated with mortality. Lots (unmixed groups) did not arrive in better condition, but experienced fewer subsequent health problems than mixed groups. (Silage-fed lots appeared to do poorly, however this was apparently due to the positive association between lots and vaccination, the latter being detrimental to mortality rates.) The more cattle per group, the greater the health problems in weeks 3-5 postarrival. Prophylactic antimicrobials in the water supply on arrival lead to increased health problems in the three to five week postarrival period. Antibiotic containing starter rations had a beneficial effect on health status in this period. This effect appeared to be partly due to delaying making silage the major ration component in silage-fed cattle receiving antimicrobial containing starter rations. Vaccination against respiratory disease in either of the first two weeks postarrival had detrimental direct and indirect effects on subsequent health status. Vaccination during weeks 3-5 postarrival was not significantly related to health status in that period.     

Laminitis-like changes in the claws of feedlot cattle

The purpose of this study was to observe and quantitate changes in the claws of two groups of feedlot cattle (calves and backgrounded yearlings) fed diets that varied in energy (73.5 or 78.5% TDN) and crude protein (11, 13, 15, 16, 17, or 19%) content. At slaughter, the thickness of sole horn and the prevalence of toe and heel hemorrhages were greater in calves than in yearlings (p<0.02). Feeding the high-energy ration increased the prevalence of toe and heel hemorrhages in calves (p<0.02) and heel hemorrhages in yearlings (p<0.02). In yearlings, rotation of the distal phalanx and ridging of the dorsal wall of the claw were the most prominent pathological features. Osteopathy of the apex of the distal phalanx occurred more frequently in calves than in yearlings (p<0.01). This study suggests that intensive feeding of beef cattle before they reach 14 months of age has a deleterious effect on digital health.     

Feeding untreated and pasteurized waste milk and bulk milk to calves: effects on calf performance,health status and antibiotic resistance of faecal bacteria

Non‐saleable milk (waste milk, WM) is contaminated with an undefined spectrum of potentially harmful pathogens and antimicrobial residues. The objective of this study was to determine the impact of feeding bulk milk (BM) or WM – both pasteurized or not – on calf performance, health and the antibiotic resistance of specific faecal bacteria. A total of 114 calves from a large‐scale dairy were housed outdoors in individual hutches and were randomly assigned to one of four feeding groups. The calves were fed either WM, pasteurized WM (pWM), BM or pasteurized BM (pBM) from day 3 to 56 of life. Milk samples taken from the pasteurizer and calves’ nipple buckets were investigated at regular intervals for total plate count and counts of thermoduric bacteria, coliforms and mastitis pathogens. Faecal samples were taken on days 2, 14, 28 and 56 of life from randomly selected calves of the WM, pWM and BM groups (each N = 8–9) and processed to obtain from each sample preferably two isolates of Escherichia (E.) coli and Enterococcus spp. respectively. Isolates were tested for their antimicrobial susceptibility to 25 antimicrobial agents by broth microdilution. Daily weight gain, milk and calf starter intake and health parameters did not differ significantly between the calves of the four feeding groups. The proportion of resistant E. coli isolates was significantly higher in calves fed WM and in calves fed pWM (most pronounced for cephalosporins) than in calves receiving BM. No differences in resistance were found for Enterococus spp. Thus, the concerns for selecting resistant faecal bacteria by feeding WM seem to be justified. Nonetheless, pasteurized WM of cows not treated with antimicrobials represents an acceptable feed for young calves.     

牧场犊牛发病次数与生长发育的关系

通过对全国157 个规模化牧场在2020年1—12 月出生的220 日龄内母犊牛各阶段发病次数、体重和日增重进行分析,旨在研究犊牛不同阶段发病次数对其后期体重、日增重的影响。结果表明:(1)断奶前后,60 日龄内发病次数≥2 次的犊牛,61~129 日龄体重、日增重极显著低于未发病犊牛和发病次数为1 次的犊牛(P<0.01);(2)转育成时,60 日龄内发病次数≥2 次的犊牛,转育成171~219 日龄体重极显著低于未发病犊牛和发病次数为1 次的犊牛(P<0.01);60~179 日龄发病次数≥1 次,转育成171~219 日龄体重和转育成日增重极显著低于未发病组(P<0.01)。因此,犊牛发病次数越多,后期生长发育越缓慢,建议牧场重视并加强犊牛断奶前后和转育成的饲养管理,做好疾病防治,以减少发病次数。     

The relationship between the occurrence of undifferentiated bovine respiratory disease and titer changes to Haemophilus somnus and Mannheimia haemolytica at 3 Ontario feedlots.

The association between exposure to Haemophilus somnus and Mannheimia haemolytica (formerly Pasteurella haemolytica) and the risk of undifferentiated bovine respiratory disease (UBRD) was investigated using serological evidence of exposure coupled with a factorial design vaccine field trial. Measures of previous exposure (titer at arrival) and current exposure (titer increase in the study period) to these agents were used. The vaccine field trial involved systematic allocation of animals into groups that received either a M. haemolytica vaccine, an H. somnus vaccine, a combined M. haemolytica and H. somnus vaccine, and an unvaccinated control group. Serum was collected from the 852 animals enrolled to determine titers to H. somnus, M. haemolytica, bovine coronavirus and bovine viral diarrhea virus. Vaccination with H. somnus in combination with M. haemolytica and with M. haemolytica alone reduced the risk of UBRD. The odds ratio for vaccination with H. somnus alone and UBRD risk suggested some sparing effect, but the 95% confidence limits included unity. There was no association between serological evidence of concurrent exposure to M. haemolytica and UBRD occurrence. There was an association between titer change to H. somnus and UBRD risk. However, the association changed with time of BRD treatment; animals diagnosed and treated for UBRD on or after day 10 showed little evidence of exposure to H. somnus, despite evidence of natural H. somnus exposure in the unvaccinated group. The association between titer change to H. somnus and UBRD occurrence seen in this study may be a consequence of prolonged exposure to antibiotics, rather than a causal association.     

The frequency, distribution and effects of antibodies, to seven putative respiratory pathogens, on respiratory disease and weight gain in feedlot calves in Ontario.

During 1983-85, 279 calves requiring treatment for bovine respiratory disease and 290 comparison (control) animals from 15 different groups of feedlot calves were bled on arrival and again at 28 days postarrival. Their sera were then analyzed for antibodies to seven putative respiratory pathogens. On arrival, the prevalences of indirect agglutination titers to Pasteurella haemolytica, P. haemolytica cytotoxin, Mycoplasma bovis and M. dispar were greater than 50%, the prevalence of titers to bovine virus diarrhea virus (BVDV) was approximately 40%, and the prevalences of titers to infectious bovine rhinotracheitis virus (IBRV), bovine respiratory syncytial virus (RSV) and parainfluenza virus type 3 (PIV3) were all below 25%. Seroconversion during the first month after arrival occurred in more than half the calves to P. haemolytica cytotoxin, PIV3 and RSV. Seroconversion of agglutination titers to P. haemolytica, Mycoplasma and BVDV occurred in about 40% of calves, and seroconversion to IBRV was infrequent (less than 5%). Initial titers were negatively correlated to subsequent titer changes within organism. Initial titers, and titer changes between organisms were essentially independent. Light calves had an increased risk of being selected for treatment for respiratory disease. Seroconversion to P. haemolytica cytotoxin, RSV and BVDV were predictive of respiratory disease cases, explaining approximately 69% of all respiratory disease cases in the feedlots. It was not possible to accurately predict weight gain or relapse from the serological data.     

The association between serological titers in infectious bovine rhinotracheitis virus, bovine virus diarrhea virus, parainfluenza-3 virus, respiratory syncytial virus and treatment for respiratory disease in Ontario feedlot calves.

A seroepidemiological study of the association between antibody titers to infectious bovine rhinotracheitis, parainfluenza-3, bovine virus diarrhea and bovine respiratory syncytial viruses, and treatment for bovine respiratory disease was conducted. A total of 322 calves from five different groups were bled on arrival, then one month later all cases (cattle treated for bovine respiratory disease) were rebled together with an equal number of controls (cattle not treated for any disease). Titers to these viruses varied significantly from group to group. Based on seroconversion, infectious bovine rhinotracheitis virus was active in 4.4%, bovine virus diarrhea virus in 24%, parainfluenza-3 virus in 69.5% and bovine respiratory syncytial virus in 71.3% of the cattle. Cattle with low titers to infectious bovine rhinotracheitis and/or bovine respiratory syncytial viruses on arrival, were at increased risk of subsequent treatment for bovine respiratory disease. Treated cattle also had significantly greater increases to parainfluenza-3 and/or bovine virus diarrhea viruses than control calves. Treatment rates varied considerably from group to group and were not strongly correlated with weight gain in the postarrival period.     

A morantel sustained-release bolus for the control of gastro-intestinal nematodes in grazing calves

Prophylactic (summer) and/or therapeutic (autumn) administrations of an intra-ruminal sustained-release bolus (MSRB) containing morantel tartrate were compared for the control of gastro-intestinal nematodes in grazing dairy calves over an 8-month period (December to August). The MSRB was designed to release morantel tartrate at 150 mg/day for 90 days.

Treated and untreated groups of calves grazed separate replicated pastures. Both groups of calves receiving the MSRB at the beginning of summer showed a significant mean liveweight advantage (17.7 kg and 20.7 kg for the summer and summer/autumn treated groups, respectively) at the end of the trial period, when compared with untreated calves. The liveweight advantage of calves receiving the MSRB in autumn only (6.5 kg) was not significantly different from that of the controls.

Both the summer and autumn administrations of the MSRB prevented the accumulation of Pre-Type II burdens of Ostertagia spp.

Retention rates of the MSRB were high and chemical analysis of faecal samples indicated a fairly constant release of the anthelmintic over the predicted 90-day period.

The results indicate that the MSRB is potentially useful for the control of gastro-intestinal nematodes, and particularly for the production of ’safe’ pasture. The MSRB could provide an effective alternative to integrated control based primarily on grazing management.     

Prophylactic medication of feedlot calves with tilmicosin

The parenteral administration to calves of the antibiotic tilmicosin either on arrival at a feedlot or 72 hours later was evaluated in a group of 308 steer calves. The calves were allotted to 24 pens so that there were eight replicates of the two medicated groups and eight replicates of the control group. The need for veterinary treatment was reduced significantly (P less than 0.05) during the first month of the feeding period in the two medicated groups. The medicated groups had an improved average daily weight gain (P less than 0.01) over the trial period compared with the non-medicated animals. This improved average daily gain by the medicated groups was not reduced when animals with respiratory disease were excluded from the calculations. The medicated groups also had an improved feed conversion efficiency (P less than 0.01) over the first 60 days of the feeding period compared with the non-medicated animals.     

Five field trials on the efficacy of a bovine respiratory syncytial virus vaccine

Five field trials evaluated whether immunization of beef cattle prior to weaning, at weaning, or immediately upon arrival at the feedlot with a commercial bovine respiratory syncytial virus (BRSV) vaccine would reduce subsequent treatment for respiratory disease.

Bovine respiratory syncytial virus vaccination was associated with a significant (p<0.05) reduction in treatment rate in one of three groups of calves immunized prior to weaning (−12%) and in calves immunized upon arrival at the feedlot (−4%).

There was no significant (p>0.05) effect of the BRSV vaccine on treatment rate in calves immunized at weaning, in calves immunized upon arrival at the Saskatoon bull test station, or in yearlings immunized upon arrival at the feedlot.

Although the trend in these field trials was to a sparing effect of the BRSV vaccine, the small reduction in treatment rate may not justify the cost of the vaccination program.