Research consultancy

Research consultancy

CHAPTER TWO: LITERATURE REVIEW

2.1 Poultry Production

Poultry production is a vital component of Uganda’s agricultural sector. It significantly contributes to enhancing food security and improving nutrition through the supply of high-quality animal protein, primarily in the form of eggs and meat (FAO, 2020). Beyond nutrition, poultry serves as an important income-generating activity, acting as a buffer to income fluctuations from crop farming and traditional livestock activities. Furthermore, the poultry industry holds great potential for export, particularly to neighboring countries, thereby contributing to foreign exchange earnings (MAAIF, 2019).

Poultry also plays a critical cultural role in Ugandan society, often featured in ceremonies such as dowries and communal feasts. The industry has experienced considerable transformation over the past two decades, with a marked increase in commercial production and adoption of exotic breeds like broilers and layers. However, the expansion of poultry production has been accompanied by increased use of antibiotics for disease control and growth promotion, raising concerns about the implications of antibiotic residues in poultry products (Clarke, 2004; Gerber et al., 2007).

2.2 Antibiotics

2.2.1 Definition of Antibiotics

Antibiotics are chemical substances that either kill or inhibit the growth of microorganisms, with minimal or no harm to the host (Guardabassi, 2008). They can be naturally derived (e.g., penicillin from fungi), semi-synthetically produced (e.g., amoxicillin), or fully synthetic (e.g., sulfonamides) (Guardabassi, 2008; Mara, 2001). In poultry, antibiotics are used extensively to treat diseases, enhance feed efficiency, promote growth, and maintain general flock health. However, misuse or overuse of antibiotics can lead to drug residues in animal-derived foods, posing risks to human health (Mara, 2001).

2.2.2 Classification of Antibiotics

According to Wang (2012), antibiotics are broadly classified as:

• Broad-spectrum antibiotics, which are effective against a wide range of both gram-positive and gram-negative bacteria (e.g., Doxycycline, Minocycline, Amoxicillin, Ampicillin).

• Narrow-spectrum antibiotics, which are active against specific bacteria types and are used when the pathogen is known (e.g., Erythromycin, Azithromycin, Clindamycin).

2.2.3 Mode of Action

Antibiotics exert their effects by targeting essential bacterial functions. Their modes of action include:

• Inhibition of cell wall synthesis

• Inhibition of protein or nucleic acid synthesis

• Inhibition of essential metabolite synthesis

• Disruption of the plasma membrane

These actions can be bactericidal (killing bacteria) or bacteriostatic (inhibiting bacterial growth) (Wang, 2012).

2.2.4 Common Antibiotics Used in Poultry

Antibiotics commonly used in poultry include penicillins, tetracyclines, macrolides, and aminoglycosides. While they have improved production efficiency and lowered costs for consumers (Donoghue, 2003), their overuse often results in residue accumulation in meat and eggs, especially if withdrawal periods are not observed (Mitema, 2001).

2.2.4.1 Tetracyclines

Discovered in the 1940s, tetracyclines (TC, OTC, CTC, DC) inhibit bacterial protein synthesis. They are valued for their broad-spectrum activity and low cost. However, their widespread use has led to resistance, requiring regulatory oversight (Michalova, 2004; Matsumoto, 2000).

2.2.4.2 β-lactams

This group includes penicillins and cephalosporins, which inhibit bacterial cell wall synthesis. Common veterinary drugs include ampicillin, amoxicillin, and penicillin G. β-lactam residues are linked to allergic reactions and the spread of antimicrobial resistance (Kowalski, 2007; Woodward, 2009).

2.2.4.3 Macrolides

Macrolides inhibit protein synthesis by binding to the 50S ribosomal subunit. They are widely used to treat respiratory diseases in poultry but are also subject to resistance mechanisms such as ribosomal modification and enzymatic degradation (Riviere, 2009).

2.2.4.4 Aminoglycosides

These broad-spectrum antibiotics impair protein synthesis and are used both for treatment and as growth promoters. Gentamicin, neomycin, and streptomycin are among the commonly used aminoglycosides (Mingeot-Leclercq, 1999).

2.3 Administration of Antibiotics in Poultry

In poultry farming, antibiotics are primarily administered through drinking water or feed to treat entire flocks, as individual treatment is impractical (Ramatla et al., 2017). This practice increases the risk of resistance and residue development when mismanaged.

2.3.1 Antibiotic Resistance

Antibiotic resistance arises from the excessive and inappropriate use of antimicrobials. Resistant bacteria can transfer resistance genes to other species, including human pathogens, posing a major global health threat (Levy & Marshall, 2004; Ahmed, 2012).

2.4 Chicken Diseases Treated with Antibiotics

Common poultry diseases treated with antibiotics include:

• Air sacculitis (Mycoplasma gallisepticum, E. coli)

• Fowl cholera (Pasteurella multocida)

• Infectious sinusitis and synovitis (Mycoplasma spp.)

Frequent use of antibiotics for disease control and growth promotion increases the risk of residue presence in poultry products (Kaneene et al., 1997; Miller et al., 1997).

2.5 Antibiotic Residues in Poultry Meat

Residues are remnants of drugs and their metabolites found in animal tissues post-treatment (Doyle, 2006). Improper record keeping, overdosing, and failure to observe withdrawal periods are major contributors to residue accumulation in poultry meat (Stobberingh, 2000; Bogaard, 2000).

2.5.1 Effects on Human Health

Residues can lead to:

• Allergic reactions

• Development of antimicrobial resistance

• Gastrointestinal disturbances

• Carcinogenic and mutagenic effects

• Reproductive and organ damage (Heshmati, 2015)

2.5.2 Maximum Residue Limits (MRLs)

MRLs define the highest permissible concentration of drug residues in food. Set by Codex Alimentarius, they aim to ensure consumer safety. For example, the MRL for tetracyclines in poultry muscle is 200 µg/kg (Codex Alimentarius, 2018).

2.5.3 Withdrawal Period (WP)

The WP is the time required post-treatment before animal products can be safely consumed. WPs vary by drug, dosage, route of administration, and animal species (Codex, 2018).

2.6 Prohibited Antibiotics

To curb resistance and safeguard human health, several antibiotics have been banned for use in poultry, including:

• Chloramphenicol

• Nitrofurans

• Fluoroquinolones (e.g., enrofloxacin)

These bans reflect global concern about their carcinogenicity, resistance potential, and toxicity (Castanon, 2007; Davis, 2009).

2.7 Cooking Effects on Antibiotic Residues

Studies show that while cooking may reduce residues, it does not eliminate them. Doxycycline is heat-stable, while oxytetracycline is heat-labile. Boiling generally reduces residue levels more than roasting or microwaving (Abou-Raya, 2013; Al-Ghamdi, 2000). However, strict adherence to withdrawal periods remains the only reliable method to prevent residue presence (O’Brien & Conaghan, 1985).

2.8 Methods for Detecting Antibiotic Residues

2.8.1 Chromatographic Techniques

• Thin Layer Chromatography (TLC): A quick and inexpensive method used for preliminary screening (Coskun, 2016).

• High Performance Liquid Chromatography (HPLC): More precise and widely used in analytical labs.

• Liquid Chromatography-Mass Spectrometry (LC-MS/MS): Highly sensitive and accurate, capable of identifying multiple residues simultaneously (Faleye et al., 2018).

• Enzyme-Linked Immunosorbent Assay (ELISA): Detects specific antibiotics through antigen-antibody interactions; though sensitive, it is more expensive and less accessible (Tajik et al., 2010).