Tylosin Dosage Adjustment Based on Allometric Scaling in Male Turkeys

Turkeys' body weight (BW) increases 10-fold within only 2.5 months, leading to a change in the pharmacokinetics (PK) of drugs according to allometric principles. Thus, the same dosage may lead to age-dependent variability in efficacy, in particular, to treatment failure and/or selection for resistance. The study aimed to investigate whether a non-linear dosage based on a published allometric model for tylosin clearance, may optimize the internal exposure in growing turkeys. The single dose PK study was performed on turkeys aged 6, 9.5, 13 and 17 weeks (BW from 1.75 kg to 15.75 kg). Tylosin was administered intravenously (i.v.) or orally (p.o.) according to following protocols: Dose = 31.6 × BW0.58 or Dose = 158 × BW0.58, respectively. Plasma tylosin was measured using high-performance liquid chromatography and non-compartmental PK analysis was performed. The area under the curve (AUClast) after i.v. administration was 8.90 ± 1.01; 7.51 ± 1.11; 6.54 ± 1.20 and 8.01 ± 1.75 mg × h/L in 6-; 9.5-; 13- and 17-week-old turkeys, respectively. After p.o. administration AUClast was 4.80 ± 2.92; 4.60 ± 2.45; 3.00 ± 1.49 and 3.24 ± 2.00 mg × h/L in respective age groups indicating high variability. For i.v. administration, the non-linear dosage allowed to minimize the age-dependent variability in AUC. However, due to low oral bioavailability (8-12%) and resulting interindividual variability, the proposed approach may not improve tylosin efficacy in turkeys under farm conditions.

Allometric Optimization of Enrofloxacin Dosage in Growing Male Turkeys: Empirical Evidence for Improved Internal Exposure

Rapid weight gain in turkeys causes a major change in the pharmacokinetics of drugs, leading to age-dependent variability in the internal exposure and, possibly, treatment failure and/or selection for antimicrobial resistance in young individuals. The aim of the study was to investigate whether a non-linear dosing protocol that accounts for the previously established allometric relation between enrofloxacin clearance and body weight (BW) may optimize the internal exposure to enrofloxacin in growing male turkeys. Enrofloxacin was administered four times, between the age of 5 and 16.5 weeks, when the turkeys’ BW increased from 1.47 to 14.92 kg. Enrofloxacin was given intravenously (i.v.) or orally at the dose calculated as follows: Dose = 30 × BW^0.59. After i.v. administration, the internal exposure to the drug—quantified as the area under the concentration–time curve (AUC)—was showing little age-related variation. The coefficient of variation (CV) for AUC in all individuals (15.7%) was only slightly higher than within the age groups (5.4–13.7%). After oral drug administration, CV for AUC in all individuals (22.1%) was similar as within the age groups (8.7–32.2%). These results show that intra-species allometric scaling may be efficiently implemented in the non-linear approach to enrofloxacin dosage in turkeys in order to obtain a precise internal exposure for the optimal antimicrobial effect.

The influence of age and body weight gain on enrofloxacin pharmacokinetics in turkeys-Allometric approach to dose optimization

Enrofloxacin is a concentration-dependent antimicrobial used in bacterial infections in poultry. During a few months of a turkey's life, pharmacokinetics of drugs undergoes substantial changes which may compromise their efficacy due to variability in internal exposure (measured by area under the concentration-time curve, AUC). The aim of this study was to describe the effects of age on the pharmacokinetics of a single intravenous (i.v.) and oral administration of enrofloxacin at a dose of 10 mg/kg to turkeys. It was found that during a 2.5-month-long period of growth from 1.4 to 14.6 kg, the AUC after i.v. administration increased almost threefold due to a significant decrease in the body clearance (from a mean of 0.76-0.28 L hr^-1  kg^-1 ). Over the same period, the mean elimination half-life was prolonged from 2.65 to 7.03 hr. Oral administration resulted in a similar trend in pharmacokinetic parameters. For both routes, formation of the major metabolite, ciprofloxacin, was marginal. Protein binding was not age-dependent and never exceeded 50%. Body clearance, volume of distribution and elimination half-life were subjected to an allometric analysis and a novel, nonlinear dosage protocol has been proposed to improve the internal exposure to the drug in different age groups of turkeys.

Efficacy and food safety considerations of poultry competitive exclusion products

Competitive exclusion (CE) products are anaerobic cultures of bacteria that are applied to poultry hatchlings to establish a protective enteric microbiota that excludes intestinal colonization by human food-borne pathogens. For safety of the poultry flock and human consumers, the identities of bacteria in CE products need to be known. A CE product is a culture of intestinal contents from adult chickens. It may be microbiologically defined by analysis of bacteria isolated from the culture, but many bacteria are hard to reliably isolate, identify, and characterize with conventional techniques. Sequence analysis of 16S ribosomal RNA (rRNA) genes may be more reliable than conventional techniques to identify CE bacteria. Bacteria in CE products may contain antimicrobial drug resistance and virulence mechanisms that could be transferred to the enteric bacteria of the food animal and to the human consumer. Detection methods for specific antimicrobial drug resistance and virulence genes and the integrase genes of conjugative transposons, mostly utilizing PCR technology, are being developed that can be applied to assess these risks in CE bacteria. With improvements in efficacy, bacterial identification, and detection and control of the possible risks of gene transfer, CE product technology can be made a more effective food safety tool.

Pathogens and manure management systems: a review

There has been an increasing concern about the effects of pathogens that are present in animal manure on humanand animal health. In recent years, outbreaks of food-borne diseases associated with the consumption of animal products havereceived much attention from the media in North America and Europe, leading to increased consumer concerns about the safety of their food supply. The health risks associated with animal operations depend on various factors. The most important ones appear to be related to the animal species being reared and the concentration of pathogenic microorganisms in animal manure. The ability of the pathogens to survive for long periods and through treatment to remain infective in the environment until ingested by human or animal host is an added concern. On the other hand, the role of livestock in most waterborne bacterial outbreaks has often been difficult to clarify since both humans and various wildlife species can shed the same microorganisms and thereby serve as sources of infection. This paper summarizes existing information on the main microbial pathogens present in livestock wastes, and discusses the impact of livestock wastes and agricultural drainage on microbiological quality of water, as well as available management and treatment technologies to minimize the prevalence of pathogens in animal wastes. Despite the fact that most disease outbreaks have been associated with food poisoning by cross-contamination during meat or milk processing and during finished product storage this review shows that a number of best management practices and technical solutions have been developed in the last few years that can be effective tools in minimizing the spread of pathogens from livestock operations in the environment.