Chlortetracycline remains the most versatile antibiotic for use in pigs. It has a broad spectrum of activity against respiratory and enteric bacteria, which makes it the most commonly used antibiotic in the UK. DEFRA recently published the consumption figures of antibiotics and tetracyclines (the family name of this class of antibiotics) were the most commonly used and chlortetracycline feed premixes for pigs and poultry make up the bulk of this use.

Graph 1. Therapeutic antimicrobial use in food producing animals in 2000 (tonnes)

(Source: Veterinary Medicines Directorate, DEFRA, 2001)

Because of this widespread use in pigs, resistance to tetracyclines has developed, especially to Escherichia coli, the cause of neonatal and post-weaning scours and salmonella species, but most of the respiratory pathogenic bacteria are still susceptible. The Veterinary Laboratories Agency of DEFRA has recently published this information.

Table 1. Sensitivity of several porcine bacterial pathogens to tetracyclines

Where there is a very low sensitivity then it is unlikely that chlortetracycline will work in the field and an alternative antimicrobial should be considered. The above figures are from submitted cases and therefore may have been exposed to antimicrobials prior to submission, so represent a worst-case scenario.

Chlortetracycline has also been shown to be active against Lawsonia intracellularis the cause of ileitis, which is responsible for diarrhoea and poor growth in grower pigs.

Graph 2. Comparative activity (Minimum Inhibitory Concentrations)
of chlortetracycline against L. intracellularis

(Source: McOrist et al, 1995)

In a clinical challenge trial it was shown to be highly effective in the prevention of ileitis and gave better production results than tylosin when included in the feed for 21 days.

Table 2. Chlortetracycline for the prevention of ileitis

There are a number of formulations with granular premixes, such as Aurogran® (Novartis), being the most popular form because they give a good homogeneous mix as the particle size is similar to feed particles and they are also non-dusty. Currently they are made from mycelial fermentation products, which have a maximum strength of about 15% such as Aurogran 150, which is the most economic formulation, although there are numerous 10% (100g of CTC/kg premix) products for convenience of dosing. In the near future, premixes based only on pharmaceutical grade chlortetracycline will be required in the EU and UK in particular.

Chlortetracycline remains a versatile and highly effective product for a number of infections in pigs but it should only be used where necessary, under veterinary supervision, to avoid further resistance development and loss of potency.

 

References:
Teale, C. (2002) Antimicrobial resistance in porcine bacteria. Pig Journal 49, 52-69

Trigo, E, Mendez-Trigo, A.V. and Simonson, R. (1996) Antimicrobial susceptibility profiles of Haemophilus parasuis, a retrospective study from clinical cases submitted during 1994 and 1995 to a veterinary diagnostic laboratory. Proceedings of the 14th International Pig Veterinary Society Congress Bologna, Italy, p 313

McOrist, S. Mackie, R.A. and Lawson, G.H.K. (1995) Antimicrobial susceptibility of ileal symbiont intracellularis isolated from pigs with proliferative enteropathy. Journal of Clinical Microbiology 33, 5, 1314-1317

McOrist and Morgan, (1998) An evaluation of chlortetracycline feed premix for control of porcine proliferative enteropathy (ileitis). Proceedings of the 15th International Pig Veterinary Society Congress Birmingham, England, 3, p 111

 

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