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0108 PD: Why do we need alternatives to antibiotics in calf management?

D.A. Moore Published on 21 December 2007

Preventative and low-level (feed) use of antibiotics in food animals have been incriminated as causes for antibiotic resistance in human pathogens. As a result of this concern, the European Commission has banned low-level feeding of antibiotics to cattle for growth promotion or disease prevention.

It is estimated that in the United States, animal antibiotic consumption is about eight times greater than that used for human therapy. As a result, antibiotic resistance in bacteria from food animals has been monitored on a national and local level for several decades.



The Food and Drug Administration is responsible for approving drugs used in food- producing animals. They consider an antibiotic “safe” if there is reasonable certainty of no harm to human health from the proposed use of the drug in food-producing animals.

The FDA regulatory requirements for drug approval include:

•drug efficacy
•target animal safety
•environmental assessment
•chemistry/manufacturing/quality control
•human food safety

–residue methods
–microbial safety (relatively new; scientific testing and data must provide strong assurance that products pose no significant risk to the efficacy of antimicrobials used to treat human disease)

As a result of the concerns about the risk of antibiotics used in food animals, many researchers have looked at the potentials for alternatives to using these drugs. Our research team has looked at this issue specifically with calf health and management in mind.


Why our studies?
The factors governing emergence and persistence of antibiotic resistance in calf production are numerous and complex. We have found that the pressure of antibiotic use increases multi-resistant calf fecal E. coli. However, the role of other calf management factors on the emergence of antibiotic resistance have not yet been characterized.

Study 1
Most antibiotic use on the calf ranch or dairy is in the preweaned calf group, both for treatment and prevention of common hutch-calf diseases such as diarrhea and respiratory. The first study was to determine factors associated with antibiotic resistance in fecal E. coli from pre-weaned calves. The factors we identified that were associated with increasing levels of resistance in fecal E. coli from preweaned calves on 33 farms in California included: Risk for increasing levels of antibiotic resistance was highest for calves three to 14 days compared to newborns. The risk increased with age. For each additional antibiotic treatment within six weeks of sampling, the risk of increasing level of antibiotic resistance increased 30 percent. Calves treated within five days of sampling increased the risk for higher levels of resistance by five times. Scraping or mechanically cleaning hutches between calves reduced levels of antibiotic resistance by 50 percent. Scraping manure from under the hutches weekly reduced the levels of antibiotic resistance by 70 percent.

Study 2
We evaluated the antibiotic resistance in fecal E. coli from samples taken from two- to four-week-old calves on cow/calf ranches, feedlots, dairies and calf ranches in Washington, Oregon and California. Isolates from California were more likely to be multi-drug resistant and isolates from calf ranches were more likely to be multi-drug resistant. Resistance was found in decreasing levels in isolates from feedlots, dairies and cow/calf farms. Fewer resistant isolates were found on organic dairies compared to conventional dairies.

Study 3
In the third study, we tried to determine if we could influence the development and persistence of antibiotic resistance in commensal fecal E. coli and assess whether calf health and growth could be maintained without the use of antibiotics. In this study, there were four groups of 30 dairy bull calves, each housed on a calf ranch.

1. raised in isolation without antibiotics
2. raised within ranch without antibiotics
3. raised within ranch with individual antibiotic treatments
4. raised within ranch with antibiotics in milk and individual antibiotic treatments

For calves in Group 3 (no milk antibiotics), those getting treated with antibiotics had three times higher risk for higher levels of antibiotic resistance. However, the resistance did not persist. Failure of passive immune transfer was the most significant factor for morbidity and mortality in these groups of calves. We found that antibiotics in the milk replacer were protective for calves less than one week of age but not apparently effective in older calves and the therapeutic antibiotics were protective against calf illness and death.


Study 4
From the 33 farms we evaluated in Study 1, we looked at Salmonella in the fecal samples. Of 3,686 fecal samples, 278 (7.5 percent) samples were Salmonella-positive and 55 percent of farms Salmonella-positive. The risk factors for Salmonella-positivity included:

•fewer calves shed Salmonella as they got older
•shedding lowest in closed herd dairies
•calves given antibiotics in milk replacer less likely to shed Salmonella
•calves getting antibiotics the very first day of life more likely to shed Salmonella

These studies indicate that:

1. Without antibiotics for treatment and prevention, it is difficult and labor-intensive to raise pre-weaned calves on inadequate or no colostrum.

2. We truly need to address problems of colostrum-deprived calves, high pathogen load and environmental stress factors to successfully raise calves and minimize antibiotic use.

3. The use of antibiotics in the first few days of life can increase Salmonella shedding and increase exposure of Salmonella to other calves in our large calf-rearing systems.

Clinical trials to evaluate alternatives to antibiotics

Study 5
The objectives of this study were to determine the effect of a colostrum supplement put into the milk replacer to preweaned calves for 14 days on treatment frequency and the influence on antibiotic resistance patterns in calf fecal E. coli. Ninety day-old calves arriving to a commercial calf ranch were randomly allocated to one of three groups and followed for 28 days. Calves received a milk replacer (22 percent protein/18 percent fat, medicated with tetracycline and neomycin at feed additive levels) twice daily and were housed outdoors in individual hutches.

The treatment group received 10 grams of supplemental IgG in the form of 70 grams of placebo. This group received an iso-caloric nutritional supplement (matched on protein and fat percent) without IgG for 14 days. The control group received no supplementation. The control group, placebo and treatment groups contributed to 40 percent, 35 percent and 25 percent respectively of the total 197 treatment days.

The antibiotic resistance profiles of fecal E. coli revealed high levels of multiple resistance, with 80 percent and 54 percent of isolates from two- and four-week-old calves respectively being resistant to nine or more antibiotics. There was no significant difference in multiple antibiotic resistance among the groups. There was a trend for higher levels of multiple resistance in isolates obtained from two-week-old calves who were treated within three days of sampling.

Calf diarrhea incidence was associated with low serum IgG levels, low incoming weight and not receiving supplemental IgG in the feed. Grain consumption and weight gain was significantly greater in calves receiving the colostrum or placebo supplement. There were no differences in mortality or respiratory disease incidence among groups. This study indicates that supplemental IgG for the first two weeks of life can improve the health of neonatal calves and reduce treatment costs.

The above study was repeated on other calf ranches with similar results. Additional clinical trials are being completed to assess the overall nutrition of calves to improve health.

It appears from our research that if we cannot get colostrum into our newborn calves, we have trouble rasing them without antibiotics. But, because of the concern for the development of antimicrobial resistance, the use of feed antibiotics may be out of our reach in the future. Management strategies now must be developed to reduce our dependence on antimicrobial blanket treatment of calves. PD

—Excerpts from 2007 California Animal Nutrition Conference Proceedings