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The use of antibiotics in livestock is necessary to preserve animal health in the farms but – like every antibiotics use – comprises the risk of selection of resistant bacteria with consequences for the therapy of infectious diseases in animals and if applicable in humans. This linkage to consumer protection adds societal elements to that topic. In order to secure appropriate veterinary and medical care it is essential to handle antimicrobials carefully and responsibly.
Its systematic recording is an essential part of the prudent use of pharmaceuticals. Different objectives can be pursued by this recording of antibiotics use in farm animals. On farm level the antibiotics applied can be used as indicators for the animal health status or for risk based animal and meat inspections. On the other hand, data of antibiotics use can be analysed in order to estimate the risk of selection and distribution of resistant bacteria from livestock. For a thorough assessment, however, combining these data with additional information such as the compliance with antibiotics guidelines is essential.
In 2007 and 2008, several ways to evaluate data of antibiotics use in livestock were tested in the context of the feasibility study “VetCAb”. 20 veterinary practices in Lower Saxony were recruited, and their official recordings of the application and delivery of pharmaceuticals from September, 1, 2006 until August, 31, 2007, were retrieved. In a district in North Rhine-Westphalia, similar data from 65 agricultural farms housing cattle or pigs were collected. The findings of the feasibility study as well as further considerations regarding the systematic recording and analysing of data of antibiotics use in livestock are the subject of the habilitation thesis presented.
In Germany, sales data, records of delivery by veterinarians or records of applications of animal owners can serve as data sources. Sales data can be compiled quite easily and allow a general but often less detailed estimation of the situation. Data collection at the practice or farm level requires a much greater effort and thus usually is not feasible on a large scale. However, in this approach the name and amount of the pharmaceutical, kind and number of treated animals as well as the treatment duration can be evaluated for each application or delivery. This enables specific analyses and thus is more suitable for many objectives than sales data.
If a representative sample of farms in Germany shall be investigated in order to make general statements, the sample should be selected by use of stratified selection methods. Requirements for representativeness must be chosen so that different farm sizes, animal species, age and usage groups as well as housing conditions are considered. Equally, farms from all regions in Germany must be involved in the survey.
Data on antibiotics use may – depending on the available details – be quantified either by the amount of active ingredients or by treatment frequencies. Treatment frequencies can be calculated basing on the amounts of active substances combined with standard values (index treatment frequency, e.g. nDDDA = number of defined daily doses animal) or by concrete treatment records (e.g. therapy frequency = nUDDA = number of used daily doses animal).
The accumulation of amounts per active substance or substance group is easy to understand and almost always available. However, the significance of pure amounts is limited and additionally carries the risk of misinterpretations – particularly by laymen – because of the different dosage of active substances.
The amounts of active substances can be displayed as numbers of index treatment frequencies nDDDApopulation by means of standard values regarding the dosage and the animal body weight, if the population sizes are known. This variable can be used to compare large populations with each other or between time periods. Since it is independent of records from veterinarians or animal owners it is used in cases, where concrete information of treatment frequencies is not available.
But the therapy frequency nUDDApopulation that displays the real number of treatment units (treatment days multiplied by number of active ingredients and number of treated animals) per population unit is more suitable to quantify the antibiotics use on farm level. The population unit may be the animal or the animal place, but also the livestock unit, and must always be stated. The investigated time period has to be mentioned as well. The therapy frequency can be used to describe the risk of selecting resistant bacteria since it accounts for the number of active ingredients.
Regarding an appropriate assessment of the antibiotics use the description of amounts or treatment frequencies usually must be complemented by further information. If animal health shall be assessed, quantitative or qualitative data on farm management, performance, feeding, hygiene, fattening procedure etc. are needed to be able to evaluate the farm’s individual situation and to identify improvement opportunities.
The estimation of the risk of selection and distribution of bacteria with resistance attributes follows the guidelines of prudent use of antibiotics. To assess the risk of the selection of resistances through antibiotics use in farm animals, treatment frequencies have to be linked with documentations concerning the compliance with the guidelines and with resistance data. The development of satisfactory concepts for a systematic collection and analysis of such data remains to be a future task for scientists and (veterinary) public health authorities.