4 DISCUSSION
This survey investigates AMU in comparable beef cattle production
systems and associated drivers for misuse and resistance emergence in
Nigeria. We found overall low level of practices towards AMU amongst
beef farmers. This can predispose MAR emergence. The low levels of
practices could be due to lack of sensitization of farmers on the
impacts of AMR and consequent public health implications. Antimicrobials
sales are supposed to be restricted and sold only by trained animal
health authorities. However, we found high practices of over-the-counter
purchase of antimicrobials from human pharmacy stores and drug hawkers
for use in beef farms. This could be due to lack of stringent government
regulations guiding antimicrobials sales for animal use in Nigeria.
The study found high practices of self administration of antimicrobials
among intensive beef farmers (68.4%) and semi-intensive farmers
(58.2%). This can lead to under-dosing or over-dosing on animals, a
characteristic of antimicrobials misuse (Maron et al., 2013). We
observed practices of giving only a single dose of antimicrobials once
on sick animals. The use of appropriate dose is as important as the
completion of the antimicrobial course (Maron et al., 2013). It is
noteworthy that a single dose of antimicrobials administered to an
animal has the propensity to generate AMR within pathogens populations
resident in that animal, and the repeated and continued AMU compounds
this risk (Harada & Asai, 2010). Inappropriate AMU on animals exposes
the pathogens to sub-inhibitory concentrations of the antimicrobials
(Davies & Davies, 2010), which can result as in the development of AMR.
High practices of inappropriate dosing could be due to inadequate
veterinary services (Garforth, 2015).
We also found non compliance with antimicrobials withdrawal periods
among intensive (72.4%) and semi-intensive (83.9%) farmers. Lack of
compliance with antimicrobials withdrawal periods could create low
therapeutic doses and high concentration of residues in tissues, which
in turn, could result in new pathogens with antimicrobial resistant
genes emergence (Alhaji & Isola, 2018). Additionally, this identified
antimicrobials to be used for therapeutic, prophylaxis and growth
promotion purposes in the two beef production systems. The likelihood of
AMR emergence from these purposes is dependent factors that are mainly
associated with quantity, dosage, frequency and duration of application
(McEwen, 2006). The most striking concern was the use by high
proportions of intensive and semi-extensive farmers (71.5% and 53.2%,
respectively) for promotion of growths in beef farms. AMU for growth
promotion and infection prevention in food animals significantly
contributes to AMR emergence, an escalating global public health threat
(Pokharel et al., 2020). When antimicrobials are used for growth
promotion, selective pressure is created among the pathogens, and
possibly forcing the exposed pathogens to mutate or acquire DNA pieces
to become antimicrobial resistant (Zowawi et al., 2015).
Tetracyclines, sulfonamides and penicillin, amongst others, were
observed to be significantly used in very high proportions in the farms.
This is consistent with findings that reported high level of AMU,
especially tetracycline, aminoglycoside and penicillin in food animals
in Africa (Kimera et al., 2020). The high levels usage may be due to
poor sanitation and low biosecurity practices. Most of the observed
frequently used antimicrobials are considered by WHO to be critically
important (neomycin) or highly important (oxytetracycline and
sulphonamides) for humans (WHO, 2012). Their residues in beef products
can be transferred to humans with consequent reactions.
The study identified risk routes for dissemination of antimicrobial
residues and resistance, creating potential One Health challenge. The
most probable ways are through: consumption of contaminated beef and
beef products; direct or indirect contacts with contaminated beef
animals, beef and fomites; and contaminated faeces and urine, aerosols,
as well as flies and rodents in farm environment. These are in consonant
with reports of a study that found AMR, especially resistant pathogens,
to be transmitted from food animals to humans through consumption of
food, contacts with contaminated animals and their waste products in the
environment (Marshall & Levy, 2011). Most of the farmers in Africa are
often in close contacts with animals, which facilitate resistant
pathogens transmission (Doyle, 2015). Studies have shown that food
animal products contaminated with resistant pathogens are direct
pathways to human colonization (Hong et al., 2011; Marti et al., 2013).
Food animals have been shown to be most important known pathway for the
spread of AMR to humans (Capita and Alonso-Calleja, 2013).
The findings on environmental pathway through contaminated faces and
urine, and aerosols are extremely important. It has been reported that
antimicrobial residues, resistant genes and pathogens can be
disseminated through airborne particulate matter from large cattle
feedlots (McEachran et al., 2015). Rapid and ceaseless transportation of
people and animals as well as aerosols from one place to another make
transmission of resistant pathogens easy, thereby threatening global
health, food safety, and food security (Zhao et al., 2010; Hong et al.,
2011; Li et al., 2012; Woolridge, 2012; FAO, 2016). This means that
there is higher propensity for transboundary spread of resistant
pathogens propagated in food animals in the environment via aerosols.
Some factors that include inappropriate dosage of antimicrobials, non
enforcement of laws regulating AMU, weak economic status of beef
farmers, low education and expertise of the farmers, husbandry
management systems, and poor sanitation and biosecurity at farm sites
were observed to significantly drive antimicrobials misuse in farms.
Excessive use and misuse of antimicrobials are widely identified as
major drivers for AMR as a result of the selection pressure imposed on
food animal microbiota abd consequent emergence, persistence, and
dissemination of resistant pathogens to humans (Morgan et al., 2011;
Larissa et al., 2013; Novo et al., 2013; WHO, 2014). Absence of adequate
regulations promotes misuse, residues and resistant pathogens emergence
and spread (Mtenga et al., 2011). Poverty has been reported to be a
major driver of antimicrobial misuse in developing countries (Okeke et
al., 2005).
In the present survey, Traffic Light model findings indicate that very
high proportions intensive (63.6%) and semi-intensive (57.6%) farms
are at Red risk status (Class 3) due to frequent AMU without
veterinarians’ consultations, a common practice by farmers in developing
countries, just to save costs. The predisposition to rely on personal
experience without patronizing veterinary services drives farmers to
indiscriminately use antimicrobials through unregulated supply chains.
They only consult professionals when there are complications after all
available options of therapy have been tried with no response, a common
practice found in developing countries (Kunin, 1993; Byarugaba, 2004).
In many countries such as the Netherlands, Denmark, Norway and Sweden,
the use of antimicrobials on food animals are strictly under the
veterinarians’ supervision (Cogliani et al., 2011), and such practices
are very much needed in beef farms in developing countries, especially
Nigeria.
Significant antimicrobial residues were identified in the urine of
intensively managed farms (48.4%) and semi-intensive herds (34.4%).
Food animals are estimated to excrete between 10% and 90% of the
antimicrobials ingested, either as bioactive compounds or unchanged, and
these can potentiate resistant pathogens emergence in the environment
(Li et al., 2018). As food animal production and associated consumption
of animal protein is forecast to markedly increase over the years to
come in LMICs, systematic surveillance of AMU on animals has become
imperative so as to mitigate AMR ( Cuong et al., 2018). Best
practices of biosecurity measures are also required to control and
prevent high level of infectious diseases in farms and avoid frequent
use of antimicrobials in farms.
The study was limited by use of relatively small sample size (660) for
the farmer when compared to the size of the study area. This might have
underestimated the effects of determinants on the outcomes. Lack of full
adjustments for clustering in the designed random sampling is a further
limitation. Application of central tendency measures, however, was
valuable enough to tolerate the likely imperfections in the confidence
intervals. Being a cross-sectional study, the survey did not demonstrate
causal relationship but does show associations of dependent and
independent variables.