Injection Of Oxytetracycline Research Articles

Evaluation of tree-injected oxytetracycline and antisense oligonucleotides targeting Candidatus Liberibacter asiaticus in citrus.

Huanglongbing (HLB) is a systemic disease of citrus caused by the bacterial pathogen Candidatus Liberibacter asiaticus (CLas) that limits citrus production worldwide. CLas is an obligate bacterial pathogen that multiplies in citrus trees and in the insect vector, the Asian citrus psyllid (ACP), Diaphorina citri Kuwayama. There is no cure for HLB currently and broad-spectrum antibiotics represent one possible therapeutic against disease symptoms. Single-stranded nucleic acid analogs, 2'-deoxy-2'-Fluoro-β-D-arabinonucleic antisense oligonucleotides (FANA ASOs), can modulate gene expression by enzymatic degradation or steric blocking of an RNA target. FANA ASOs recognize and bind to specific RNA forms, including mRNA, miRNA and long noncoding RNA, through complementary base-pairing. Injection of oxytetracycline (OTC) into mature citrus trees with HLB ameliorated symptoms of disease, increased fruit yield and quality of juice as compared with that produced by noninjected controls. Injection of trees with FANA ASOs reduced CLas abundance but did not improve fruit yield and quality above control levels at the injection dosage tested. Reduced pathogen relative abundance following OTC injection was coincident with lower CLas acquisition and inoculation by laboratory deployed and wild-type D. citri collected from the field, respectively. However, injections of FANA ASOs did not consistently reduce CLas transmission as compared with noninjected controls. Trunk injection of OTC may be useful in management of HLB by reducing CLas infection in trees and disrupting transmission. However, more research is needed to verify the potential usefulness of FANA ASOs. Optimizing FANA ASO dosage in trees and exploring the potential of multiplex FANA ASOs that simultaneously target multiple mRNAs could possibly enhance their efficacy against CLas. © 2024 Society of Chemical Industry.

Outbreak Of Fowlpox In Commercial Brown Pullets Previously Vaccinated With Fowlpox Vaccine In Zaria, Kaduna State, Nigeria

Fowlpox is a contagious viral disease of poultry, ranked as the third most important cause of mortality in Nigerian indigenous chickens. The present study confirms an outbreak of fowlpox in a flock of 500 Isa brown, 11-weeks-old pullets in Zaria, Kaduna State, Nigeria. The pullets were managed under deep litter system and previously vaccinated with live attenuated vaccine (ABIC biological laboratories Ltd. Israel) at 8-weeks old. They had gross lesions suggestive of cutaneous fowlpox on skin of the head region with 58% morbidity but persistent low mortality rate of 13.8%. Fowlpox virus was isolated from the cutaneous lesions using chorioallantoic membrane (CAM) inoculation in 9 to 11-day-old embryonated chicken eggs based on the presence of opaque-white pock lesions, then confirmed by Agar Gel Immuno Diffusion test using homologous known fowlpox virus (antigen) and antisera. Specific antibodies to fowlpox virus were quantified from the sera of the chickens using an indirect ELISA (Abbkine, Inc, China). The case was managed using; Intramuscular injection of oxytetracycline (TLA), topical applications of oxytetracycline spray as well as oral administrations of Doxygen® and vitamins. Apparently healthy chickens were revaccinated against fowlpox and the pen was thoroughly cleaned, washed, and disinfected. This report had shown an occurrence of vaccine failure, alongside a promising management option and highlighted the significance of vaccination with strict biosecurity measures in the control of fowlpox in Nigeria.

Trunk injection of oxytetracycline improves plant performance and alters the active bark and rhizosphere microbiomes in huanglongbing-affected citrus trees

Trunk injection of oxytetracycline improves plant performance and alters the active bark and rhizosphere microbiomes in huanglongbing-affected citrus trees

Therapeutic Management of Cytauxon Felis in Cat

A Persian cat that was 4 months old and weighed 2 kg was brought to the Parel campus of the Mumbai Veterinary College in Mumbai, Maharashtra. Anorexia, pyrexia, and bodily weakness in the past. Clinical evaluation revealed the patient had a high temperature (104.3°F), was anemic, looked dull, and was dehydrated. Low hemoglobin, a low platelet count, and elevated liver enzyme levels are shown by a complete blood count, liver function tests, and kidney function tests. The cat was initially treated with injections of Oxytetracycline at 10 mg/kg body weight for three days before being switched to susp. Azithromycin at 10 mg/kg B.W. plus Tab. Atovaquone at 15 mg/kg B.W. along with fluid therapy, injections of Acetyl-cysteine at 140 mg/kg and then reduced to 50 mg/kg B.W., as well as oral multivitamins and pre-probiotics. Cat displayed full healing following 20 days of therapy.

Insights into vertebral band pair deposition rate in the juvenile common thresher shark (Alopias vulpinus) in the northeastern Pacific Ocean.

Validation of band pair deposition rates in elasmobranch vertebrae is essential for accurate age estimation using band pair counting techniques. We present a validation study of the vertebral band pair deposition rate for juvenile common thresher sharks Alopias vulpinus in the northeastern Pacific Ocean (NEPO) using tag and recapture with oxytetracycline (OTC) injection. A total of 14 juvenile A. vulpinus marked with OTC from 1998 through 2013 were recaptured with times at liberty ranging from 1.08 to 3.81 years with an average of 2.14 years (±0.97 years standard deviation, SD). Shark size ranged from 80 to 128 cm fork length (LF) at the time of OTC injection and from 112 to 168 cm LF for those measured at recapture. The slopes of the relationships between band pairs post OTC and years at liberty for each reader ranged from 0.84 to 0.95, slightly lower than the 1.0 slope expected from annual band pair formation. These findings preliminarily support previous age and growth assumptions based on a one band pair per year deposition rate. However, high variation in band pair deposition rates between samples, coupled with regression slopes falling just under one band pair per year, indicates that further investigation is needed to refine band pair deposition rate estimates.

Wound reaction to trunk injection of oxytetracycline or water in huanglongbing-affected sweet orange (Citrus sinensis) trees

Key messageTrunk injection causes injury to trees and best practices must be established for use of this technology to manage vascular diseases such as huanglongbing.Trunk injection is a technique for applying plant protection compounds that has demonstrated efficacy for management of huanglongbing (HLB), a bacterial disease which has devastated the Florida citrus industry. Recently, the antibacterial oxytetracycline has been approved for trunk injection in citrus in Florida. Despite its potential for restoring health of HLB-affected trees, little information is available on the trees’ ability to heal and compartmentalize the wounds caused by trunk injection and the interaction with season and other factors. In this study, 5-year-old HLB-affected sweet orange (Citrus sinensis) trees were injected bi-monthly to measure seasonal differences in the rate of uptake of injected water and to compare the external and internal wound reaction in both scion and rootstock. Also investigated was the wound reaction after trunk injection of an injectable formulation of oxytetracycline. Injection during spring and summer promoted more rapid wound closure compared to injection in fall or winter, and injection into the scion was less damaging than injection into the rootstock. Although citrus trees effectively compartmentalized wounds inflicted by injection of water, injection of oxytetracycline impeded wound healing and increased internal damage. Application of a fungicide or pruning sealant increased the size of the wound internally and externally. For trunk injection to be adopted for use in commercial citrus orchards, the benefits of injection must outweigh the risks of wounding associated with the application method. This study provides first insight on some of the best practices for effectively utilizing trunk injection in citrus as a crop protection strategy.

Evaluation of Trunk Injection Techniques for Systemic Delivery of Huanglongbing Therapies in Citrus

The bacterial pathogen associated with citrus huanglongbing (HLB) resides in the phloem of affected trees. The widespread abundance of the vector in Florida, the Asian citrus psyllid (Diaphorina citri), and the location of the pathogen in the tree vascular tissue limits the efficacy of foliar-applied therapies. Trunk injection is a crop protection strategy that applies therapeutic compounds directly into the tree vascular system, enabling their systemic distribution within the tree. However, limited information is available on the most effective methodology for implementing trunk injection at the commercial scale and the extent of damage inflicted by the injection. In this study, 5-year-old HLB-affected ‘Midsweet’ sweet orange (Citrus sinensis) trees were injected with the insecticide imidacloprid, the antibacterial oxytetracycline, or water. Injections occurred in Jun and Oct 2020 using three trunk injection techniques. Trees were monitored for external wounding and internal damage associated with injection, as well as tree health, bacterial titers, and yield for two production seasons. Low-pressure injection caused the least damage; however, it was less effective at delivering the tested compounds than medium- or high-pressure injection. Despite causing the greatest extent of external and internal damage at the injection site, injection of oxytetracycline significantly improved tree health, reduced bacterial titers, and increased yield in the two seasons of this study. Imidacloprid injection caused less wound damage but did not result in any lasting benefits to the trees. These results suggest that trunk injection of oxytetracycline could be an effective strategy for managing HLB and that the damage inflicted by this crop protection strategy can be reduced by selecting a suitable injection technique.

Validation and Comparison of Age Estimates for Smallmouth Buffalo in Oklahoma Based on Otoliths, Pectoral Fin Rays, and Opercula

AbstractWith an increased interest in nongame fishes such as buffalofishes (Catostomidae, Ictiobus), there is a need for better foundational data on their life history. Bigmouth Buffalo I. cyprinellus, for example, have been found to live for more than a century. Age estimates for other sucker species have similarly suggested long life spans, but validation studies as reference points are often lacking. We conducted a 3‐year study on Smallmouth Buffalo I. bubalus in Oklahoma to validate annual increments on three hard part structures (otoliths [lapilli], pectoral fin rays, and opercula) typically used for age estimation. We marked wild fish with oxytetracycline (OTC) injection and stocked those fish into a hatchery pond to create a population of fish with known times since marking. Furthermore, reproduction in the pond allowed us to validate annulus formation in young fish. We analyzed 117 fish and found that otoliths were more reliable, precise, and accurate than the other two structures for detecting OTC marks and counting annuli. Age estimates, from 1 to 61 years, were greatest when otoliths were used, with 99% of estimates corresponding to known time since marking or known age. Otoliths appear to be the only reliable structure for accurately estimating the age of Smallmouth Buffalo within 1 year of actual age, and their use indicates that this species can live for more than six decades in Oklahoma.

Trunk Injection of Oxytetracycline for Huanglongbing Management in Mature Grapefruit and Sweet Orange Trees.

Huanglongbing (HLB) is a devastating bacterial disease associated with 'Candidatus Liberibacter asiaticus'. The location of the pathogen within the vasculature of the tree has left growers with limited options for the effective management of the disease. Trunk injection is a crop protection technique that applies therapeutics directly into the xylem of woody tree species and allows for their systemic uptake and transport, which may provide more effective management of vascular diseases such as HLB. In this study, mature 'Valencia' and 'Hamlin' sweet orange (Citrus sinensis) and 'Duncan' grapefruit (C. paradisi) trees were injected with oxytetracycline (OTC) in the spring and/or fall to evaluate the effects of injection timing and response to injection. In addition to seasonal evaluations of tree health and bacterial titer, preharvest fruit drop, yield, and fruit quality were measured at harvest to determine the effects of OTC injection. The benefits associated with injection included a reduction in fruit drop, an increase in fruit yield and fruit size, and improvements in juice quality. However, results varied due to the timing of injection and were not consistent across all three varieties. Residue analysis at different time points after injection suggests that trunk injection effectively delivers therapeutics to mature citrus trees. This study provides fundamental information on the short-term benefits associated with trunk injection of OTC for HLB management in citrus groves. The potential for use of trunk injection at the commercial scale and the possible risks are discussed.

Efficacy of different treatment protocols for endometritis in Camelus dromedarius.

Endometritis is considered a significant cause of infertility problems in dromedary camels. This study aimed to compare the efficacy of different treatment protocols for endometritis in dromedary camels under Abu Dhabi Emirates' conditions. A total of 112 dromedary she-camels with uterine infection were subjected to uterine swabbing for bacterial culture and received one of the following treatments: (i) uterine douching with lotagen every other day for three doses, (ii) single parenteral oxytetracycline injection, (iii) subcutaneous injection with ceftiofur for 5 days, or (vi) combined oxytetracycline-ceftiofur injection. The results showed that Escherichia coli was the most isolated bacteria, followed by Streptococcus species. Treatment efficacy was (P < 0.05) higher in ceftiofur and oxytetracycline-ceftiofur protocols compared with lotagen and oxytetracycline protocols. The fertility indexes, services per conception and pregnancy rate, were improved in ceftiofur and mixed oxytetracycline plus ceftiofur protocols as the pregnancy rate was (P < 0.05) higher in those protocols compared with lotagen and oxytetracycline protocols (71.4 and 67.9% vs. 39.3 and 42.9%, respectively). On the other hand, the number of services per conception was significantly lower in ceftiofur and oxytetracycline-ceftiofur protocols (1.2 for each protocol) than in lotagen and oxytetracycline protocols (1.8 and 1.7, respectively). In conclusion, subcutaneous injection of 1 ml ceftiofur per 50 kg body mass for 5 days can be used as an efficient treatment for uterine infection in female dromedary camels caused by E. coli and Streptococcus species for improving their fertility indexes.

Development and validation of an ultraviolet-visible spectrophotometric method for quantifying oxytetracycline for veterinary use

Livestock breeding plays a key role in sub-Saharan Africa because it is an important source of highly valued protein in the human diet, and because it is an essential driver for socio-economic development. It represents a form of investment and is also important from a socio-cultural point of view (ceremonies, social position, etc.). Livestock is an important source of income, livelihood, nutrition, and food security. However, livestock breeding faces, among other things, major sanitary constraints. Furthermore, the circulation of non-compliant antibiotics on the market constitutes a major threat to animal health, public health, and the environment. This research aims to develop and validate a UV-vis method for quantifying pharmaceutical oxytetracycline. The method developed was validated following the total error strategy as a decision tool in the accuracy profile. After its completion, the method demonstrated good absolute and relative bias and was within a tolerable interval of [−2%, +2%]. The method was also repeatable with intermediate precision, with respectively lower values than 2% and 4%. We also assessed the recovery and accuracy of the method as fitting with the specification limits. After its validation, the method was quantified in 47 oxytetracycline injectable samples, where we obtained 28 samples complying with specifications and 19 that did not. That led us to conclude that the developed method was validated and appropriate for quantification in terms of the routine quality control of oxytetracycline injection. The method needs to be reviewed and revalidated accordingly for other pharmaceutical presentations.

Systemic Uptake of Oxytetracycline and Streptomycin in Huanglongbing-Affected Citrus Groves after Foliar Application and Trunk Injection.

Huanglongbing (HLB), which is caused by the phloem-limited bacterium ‘Candidatus Liberibacter asiaticus,’ is an economically important disease of citrus in many regions of the world. Due to the significant damage caused by the HLB disease in recent years, the use of antibiotics was recommended for the therapy of this destructive disease. Products with active ingredients oxytetracycline and streptomycin have been approved for the control of the HLB via foliar application. However, previous work raised questions about the efficacy of foliar delivery of antibiotics in the field. In this study, we examined the effects of a variety of adjuvants on the uptake of oxytetracycline and streptomycin using the foliar application. We also compared the efficiency of foliar application of oxytetracycline and streptomycin with trunk injection. The ‘Ca. L. asiaticus’ titers in citrus plants were measured using quantitative PCR, and the levels of antibiotics were determined using the ELISA assay. Our results include extremely low levels of oxytetracycline and streptomycin in leaves that were covered during foliar application, indicating that neither streptomycin nor oxytetracycline was successfully systemically delivered by foliar application even after being mixed with adjuvants. Likewise, the ‘Ca. L. asiaticus’ titer0 was not affected by any of the foliar applications. High levels of streptomycin were detected in leaves that were exposed to direct foliar application, indicating that streptomycin was adsorbed or bound to citrus leaves. On the other hand, the trunk injection of oxytetracycline resulted in high levels of this antibiotic in leaves and significantly reduced the level of ‘Ca. L. asiaticus’ titer in citrus trees. Unfortunately, the trunk injection of streptomycin resulted in low levels of streptomycin in citrus leaves and did not affect the ‘Ca. L. asiaticus’ titer, indicating that streptomycin was either bound in the xylem of citrus trees or it was not applied in sufficient quantity required for the inhibition of ‘Ca. L. asiaticus.’ Taken together, our current results demonstrated that foliar application of oxytetracycline and streptomycin did not effectively deliver antibiotics in citrus despite using adjuvants. Our results also suggested that oxytetracycline could be more effective against the HLB pathogen than streptomycin, which is possibly due to differences between the two in systemic movement in citrus trees.

Isolation of Aeromonas hydrophila in a case of wound infection in cattle in Nigeria

A three and a half year old N'dama cow weighing about 150kg was rescued from a steel jaw trap during grazing the previous day and presented at the Teaching and Research Farm Federal University of Agriculture, Abeokuta, Nigeria with a fresh, deep wound. The animal was treated but there were no satisfactory response to Penicillin/streptomycin intramuscular injection at 10,0001U/kg for seven days and also i/m 20% Oxytetracycline injection at 20mg/kg repeated after 48 hours. A loopful of pus samples aseptically taken from the wound were streaked on blood agar base enriched with 7% horse blood (Oxoid, UK) using the quadrant streaking method and incubated aerobically at 37°C for 24-48 hours. Aeromonas hydrophila was isolated which was resistant to the commonly used antibiotics on the farm. Following the results obtained from the sensitivity test, the animal was placed on Enrofloxacin for seven days, the swelling regressed, no pus was expressed from the wound site and no pain was elicited from the joint on application of pressure by the 8th day Aeromonas hydrophila is pathogenic to man; hence care should be taken in handling of animal traps.

Growth and Age Validation of the Thornback Ray (Raja clavata Linnaeus, 1758) in the South Adriatic Sea (Central Mediterranean)

Raja clavata is the most widespread and landed skate species in the Mediterranean Basin. Despite its diffusion and economic importance, several aspects of its life history, such as age and growth, are poorly understood. This study evaluated the species’ growth in the South Adriatic Sea (Central Mediterranean Sea) and for the first time attempted an age validation through a tagging experiment. Thin sectioning of vertebral centra proved to be a more accurate preparation method in terms of age estimation precision and reproducibility than whole vertebral centrum staining (cobalt nitrate and ammonium sulfide technique). Marginal analysis showed a clear seasonal pattern, confirming the hypothesis of a single annulus deposition per year. A total of 291 vertebral centra were sampled and used for age estimation purposes. The oldest female was estimated to be 12 years old [total length (TL) = 89 cm], while the oldest male was aged 8 years (TL = 79.9 cm). Females were also found to be characterized by a slightly wider longevity range (ωL = 11.5, ωU = 16.8 years) than males (ωL = 7.8, ωU = 11.2 years). The von Bertalanffy growth curve fit the age and length data more accurately than the Gompertz and logistic models. Eighty-three thornback rays were tagged and released, of which two were recaptured. In both recaptured specimens, oxytetracycline marks were clearly visible. The band deposition after oxytetracycline injection and growth during the freedom period (about 1 year) were consistent with the age estimation method and criteria used and with the obtained growth results. Thus, the analysis of the vertebral centra extracted from the two recaptured specimens confirmed the hypothesis of the deposition of a single annulus per year and in general the age estimation criteria used in this study.

An alternative cold chain for storing and transporting East Coast fever vaccine

East Coast fever (ECF) is an often fatal, economically important cattle disease that predominantly affects eastern, central, and southern Africa. ECF is controlled through vaccination by means of simultaneous injection of oxytetracycline and cryogenically preserved stabilate containing live, disease-causing parasites. Storage and transportation of the stabilate requires liquid nitrogen, a commodity that is commonly unreliable in low-resource settings. Here we show that storage of conventionally prepared stabilate at −80 °C for up to 30 days does not significantly affect its ability to infect cultured peripheral blood mononucleated cells or live cattle, suggesting an alternative cold chain that maintains these temperatures could be used to effectively manage ECF.

Evaluation of intramuscular injection of oxytetracycline for use as an experimental model to induce pain and assess the efficacy of pain mitigation strategies in dairy cows.

To evaluate IM injection of oxytetracycline as an experimental model to induce pain and assess the analgesic efficacy of flunixin meglumine (FM) in dairy cows. 15 healthy nonlactating Jersey (n = 10) and Holstein (5) cows. In the first of 2 experiments, 5 Jerseys were administered oxytetracycline (10 mg/kg, IM), divided between the right side of the neck and left hind limb. The left side of the neck and right hind limb received sham injections. Cows were also randomly assigned to receive FM (2.2 mg/kg, IV; n = 3) or an equal volume of saline (0.9% NaCl) solution (0.044 mL/kg, IV; control; 2) once daily for 5 days. The mechanical nociceptive threshold (MNT) was measured before oxytetracycline administration and at predetermined times after each injection of the assigned treatment. Experiment 2 was similar to experiment 1 except it involved 5 Jerseys and 5 Holsteins, oxytetracycline was injected only in a hind limb, and the assigned treatment was administered for 10 days. For both experiments, mean MNT for the oxytetracycline injection site was consistently less than that for the sham injection site in the hind limbs, and mean MNT at the hind limb oxytetracycline injection site for FM-treated cows was greater than that for control cows beginning on day 3. IM injection of oxytetracycline in a hind limb reliably induced signs of pain in dairy cows and, with validation, might be useful as an experimental model for assessing pain mitigation strategies in cattle.

First report of Dermatophilus congolensis infection in native Omani cattle.

Skin lesions were reported in a group of quarantined Omani native cattle for exportation purpose during January 2018. The skin lesions were reported in 17 animals out of 140 and were scattered over the head, neck, back and perineal region of the animals. Lesions varied from paint-brush matted hairs to wart-like lesions that are up to 2 cm in diameter. Skin scraping samples were obtained from the living animals and were directly stained with gram stain. Histologically, there was severe multifocal exudative dermatitis with hyperkeratosis. Dermis was infiltrated with neutrophils, mononuclear cells, and numerous branching filaments coccoid bodies. Bacterial culture on sheep blood agar revealed gray to white, beta hemolytic, raised and irregularly shaped colonies. Gram staining showed gram positive branching filaments with both transverse and longitudinal fragments formed from packs of coccoid cells confined with Dermatophilus congolensis. Animals were treated successfully with 3 doses of intra muscular injection of long-acting oxytetracycline with topical application of antibiotic spray. To the best of our knowledge, this is the first report of dermatophilosis in Omani cattle.

The in Planta Effective Concentration of Oxytetracycline Against 'Candidatus Liberibacter asiaticus' for Suppression of Citrus Huanglongbing.

Huanglongbing (HLB) or greening currently is the most devastating citrus disease worldwide. The fastidious phloem-colonizing bacterium 'Candidatus Liberibacter asiaticus' (CLas) is the causal agent of citrus HLB in Florida. Bactericides containing the active ingredient oxytetracycline (OTC) have been used in foliar spray to control citrus HLB in Florida since 2016. However, the minimum concentration of OTC required to suppress CLas in planta remains unknown. We developed a new method for evaluating the effects of OTC treatment on CLas titers in infected plants and determined the relationship between OTC residue levels and control levels achieved for CLas using mathematical modeling in greenhouse and field experiments. In both greenhouse and field, OTC spray did not reduce the titers of CLas, and it produced undetectable or mild levels of OTC residue in leaves within 7 days post-application (DPA). In greenhouse, OTC injection at 0.05 g per tree decreased CLas titers to an undetectable level (cycle threshold value ≥ 36.0) from 7 to 30 DPA and produced a residue level of OTC at 0.68 to 0.73 µg/g of fresh tissue over this period. In the field, OTC injection at 0.50 g per tree resulted in the decline of CLas titers by 1.52 log reduction from 14 to 60 DPA, with residue levels of OTC at 0.27 to 0.33 µg/g of fresh tissue. In both trials, a first-order compart model of OTC residue dynamics in leaves of trunk-injected trees was specified for estimating the retention of effective concentrations. Furthermore, nonlinear modeling revealed significant positive correlations between OTC residue levels in leaves and the control levels for CLas achieved. The results suggested that the minimum concentrations of OTC required to suppress CLas populations in planta to below the detection limit are 0.68 and 0.86 µg/g and that the minimum concentrations of OTC required for initial inhibition of CLas growth in planta are ∼0.17 and ∼0.215 µg/g in leaf tissues under greenhouse and field conditions, respectively. This finding highlights that a minimum concentration of OTC should be guaranteed to be delivered to target CLas in infected plants for effective control of citrus HLB.

Validation of Annuli and Identification of Discontinuities in Sagittal Otoliths of Juvenile Alligator Gar

AbstractAnnual increment periodicity has been validated in sagittal otoliths of Alligator Gar Atractosteus spatula; however, discontinuities (often referred to as false annuli or checks) are common in early years, potentially affecting both accuracy and precision. We used up to four injections of oxytetracycline (OTC) to induce time stamps associated with annuli (opaque zones) in the otoliths of juvenile Alligator Gar (ages 2–6; n = 68). These OTC marks allowed us to test a reader's ability to distinguish discontinuities (hereafter, “checks”) from annuli by using established criteria. In addition, the OTC marks were used to infer the timing of translucent zone and opaque zone formation. Although the reader's error rate was low (6%), some checks were essentially indistinguishable from annuli. Checks were common, occurring in over half of the otoliths examined and within all annual increments in these juvenile fish. The association of all OTC marks with the opaque zones of the annual increment further validates annulus formation in juvenile Alligator Gar and indicates that these narrow zones formed approximately between November and June. Subsequently, it can be inferred that the much wider translucent zones formed from about June to November. Although opaque zone formation was complete by June, new annuli were not distinguishable from the ventral edge of the otolith until translucent material was deposited beyond the annuli. In our samples, only 22.2% of the otoliths from fish sacrificed on June 30 (n = 9) had fully visible annuli along the edge of the otolith. Based on multiple studies, it is apparent that annual increments form in the sagittal otoliths of Alligator Gar throughout their lives; however, the interpretation of these increments can be very difficult. In our experience, the OTC marking of fish can provide a valuable tool for training and verification programs needed for this species and for other long‐lived fishes that pose difficulties in age estimation.

Shifts in the nasal microbiota of swine in response to different dosing regimens of oxytetracycline administration

The impacts of antibiotic treatment and dosing regimen of an antibiotic on the swine respiratory microbiota are poorly defined. To begin to address this, this study characterized the impact of oxytetracycline administration, given either parenterally or in feed, on the diversity of the nasal and tonsil microbiotas of post-weaned pigs over a two-week period. One group received a single intramuscular injection (IM) of oxytetracycline, the second was treated with oxytetracycline mixed in feed (IF), and the control group received non-medicated (NON) feed. Nasal samples were collected on days 0 (before start of treatment), 4, 7, 11, and 14. Tonsil tissue samples were collected from a subset of pigs selected for necropsy on days 4, 7, and 14. The results showed that the tonsil microbiota was stable regardless of antibiotic treatment. In contrast, the nasal bacterial diversity decreased for both oxytetracycline-treated groups compared to NON. The IF group also exhibited decreased diversity on more days than the IM group. The nasal bacterial community structures of the antibiotic treatment groups were significantly different from the NON group that persisted from day 4 until day 7 for the IM group, and up until day 11 for the IF group. This included relative increased abundances of Actinobacillus and Streptococcus, and relative decreased abundances of multiple commensal genera. The microbiota of the IF group was also more disturbed than the microbiota of the IM group, relative to NON. This study revealed that short-term exposure to broad-spectrum antibiotics like oxytetracycline can disturb the upper respiratory microbiota, and the dosing regimen has differential effects on the microbiota.