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Item The disposition of gentamicin in equine plasma, synovial fluid and lymph : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University(Massey University, 1993) Anderson, BrianAlthough it is easy to monitor blood concentrations of antimicrobials most bacterial infections occur in extravascular sites, more specifically within the interstitial fluid. It is very difficult to sample interstitial fluid and many different methods have been used. Reports of the relationship between blood and interstitial concentrations of antibiotics have varied depending on the tissue/tissue fluid sampling technique used. The sampling of tissue fluid for antimicrobial studies in horses has been limited. Most studies have measured antibiotic concentrations in readily accessible body fluids such as urine, peritoneal fluid and synovial fluid. The relationship between these fluids and interstitial fluid in the horse is not known. The disposition of gentamicin in equine plasma, synovial fluid and in peripheral lymph was studied. A lymph vessel (dorsal digital lymph trunk) on the medial aspect of the distal hindlimb was selected for the disposition study. To better define the relationship between synovial fluid and tissue concentrations of an antimicrobial it was shown that this vessel had a contribution to its lymph derived from the synovium of the fetlock joint. Very high concentrations of gentamicin were retrieved in the lymph collected from the cannulated vessel after intra-articular injection (150mg dose). The mean maximum lymph gentamicin concentration was approximately 50 μg/ml and the time to reach this, approximately 1.7 h after joint injection. The mean synovial fluid concentration 0.25 h following injection was 7244 ± 660 μg/ml and disappearance from the synovial fluid was consistent with first order kinetics with a mean disappearance half-life (harmonic mean) of 0.99 (0.83-1.22) h. A technique for chronic cannulation of the dorsal digital lymph trunk was developed. Two Trials were conducted and in the first (Trial A) the disposition of gentamicin in plasma and lymph was studied after intravenous injection (2.2 mg/kg). In Trial B the disposition of gentamicin in plasma, synovial fluid and lymph was studied. Kinetic parameters were similar to other reported studies. There was no significant difference in kinetic parameters between trials. The disposition curves for all three fluids were similar. Mean maximum lymph concentrations were approximately 4.6 μg/ml and were 40% of the plasma concentrations 15 minutes after injection. These were achieved approximately 1.35 h after injection. The maximum concentration of gentamicin in synovial fluid (2.86 ± 0.45 μg/ml) was significantly less than in lymph. Three hours after injection plasma, synovial fluid and lymph concentrations were very similar and it was concluded that a sample of any one would be a good index of the others at this time. The relationship between synovial fluid and tissue fluid 3-8 h after injection was less clear with marked divergence of the disposition curves. Gentamicin was more slowly eliminated from lymph than plasma but a parallel relationship between the two fluids was observed 3-8 h after injection, with a mean lymph:plasma ratio of approximately 1.6. It was concluded that plasma concentrations were a good index of tissue fluid concentrations. Maximum lymph concentrations of gentamicin after intravenous injection were 10 times less than after intra-articular injection. The presence of very high concentrations in lymph derived from the synovium of a joint after intra-articular injection suggest that subsynovial interstitial fluid concentrations are also this high and therefore that intra-articular injection may have some therapeutic advantage over systemic injection. Lymph cannulation in the horse appears to be a viable technique for antimicrobial disposition studies.Item Equine gastric ulcer syndrome in New Zealand racehorses : a thesis presented in partial fulfilment of the requirements for the degree of Master of Veterinary Science at Massey University, Palmerston North, New Zealand(Massey University, 2006) Bell, Robin Joseph WallaceAims To establish the prevalence of gastric ulcers in New Zealand racehorses. Methods A prevalence study was conducted during 2003 and 2004 in New Zealand. One hundred and seventy one horses from 24 trainers across New Zealand were examined with gastroscopy as part of the study. Images of the examination were recorded and reviewed. The stomachs were assigned an ordinal score based on the severity of the gastric ulceration present. Results There were 171 horses in the study: 133 Thoroughbreds and 38 Standardbreds. One hundred and fifty one (88.3%) of these had evidence of EGUS. There was no significant difference in the prevalence of ulceration between the two breeds (p=0.51) or between horses of differing ages (p=0.56). There were 141 horses kept at pasture for at least four hours per day, of these 125 (89%) had EGUS. Thirteen horses were kept at pasture full time and all of these had EGUS. Seventeen horses were stabled full time and 16 (94.1%) of these had EGUS. There was no significant difference between the different housing groups and the prevalence or severity of EGUS (p=0.33 and 0.13 respectively), and there was no significant difference in the severity of gastric ulceration (p=0.12) between the horses grazed on different pasture qualities. There was no significant difference in the prevalence (p=0.26) or severity (p=0.49) of gastric ulceration based on the duration of training. Conclusions The prevalence of EGUS in New Zealand racehorses is similar to that reported elsewhere for horses in active race training. The type of turnout that these horses receive does not appear to be protective for EGUS. Clinical relevance Pasture turnout alone may not be protective against EGUS in racehorses that are in active training. Gastric ulceration is a common problem in New Zealand racehorses and may be a cause of decreased performance in these animals.Item Epidemiology of equine herpesvirus infections : a thesis presented in partial fulfilment of the requirement for the degree of Master of Philosophy in Veterinary Science at Massey University(Massey University, 1985) Fu, Zhen FangThe epidemiology of infections with equine herpesvirus (EHV) types 1 and 2 in foals on a Thoroughbred stud in New Zealand was investigated. As part of this study an ELISA test was developed to measure antibody titres to EHV-2 in equine sera. All the sera collected from the foals before the ingestion of colostrum were negative for antibodies to both EHV-1 and EHV-2. Soon after sucking, these foals had serum antibody levels against these two viruses similar to those of their dams. The maternally derived antibody to EHV-1 lasted for 3-4 months and antibody titres rose again at around weaning time. In contrast, passively acquired antibody to EHV-2 was rapidly supplemented by actively produced antibody. Serological evidence suggested that most of the foals (85%) became infected with EHV-1, and 25% were reinfected in their first ten months of life; however EHV-1 was not recovered either from these mares or their foals during the investigation period despite the large increase in antibody titres. Serological evidence of EHV-1 infection in foals indicated that this occurred around the time of weaning when the maternally derived antibody had declined to a level which was presumably unprotective. The clinical signs which developed after EHV-1 infection were very mild, the main symptom observed being a profuse nasal discharge usually lasting two or three days, occasionally with an elevation of body temperature. The source of EHV-1 infection in foals could not be determined and there was no evidence to suggest that their dams were infected with EHV-1 around the time when the foals became infected. However, a relationship between preinfection antibody titres (log 103) against EHV-1 and the viral infection was observed. In contrast, EHV-2 was isolated from all of the foals by 2 to 4 months of age. The virus infection persisted in these animals for 2 to 6 months and stimulated continuous production of antibody. As soon as the antibody level against EHV-2 reached a peak, the isolation of the virus decreased, and eventually EHV-2 was no longer isolated from these foals by 9 months of age. The foals possibly contracted EHV-2 infection from their dams since some of them excreted the virus around the time when EHV-2 was isolated from their foals. Clinical reactions at around the time of EHV-2 infection varied from foal to foal, ranging from subclinical to fever, mucopurulent nasal discharge and swollen submandibular lymph nodes. Two severely affected foals from which EHV-2 was isolated died of complications resulting from secondary bacteraemia. From these findings, an association between EHV-2 and the respiratory disease observed in these foals was postulated. However, the possible role of EHV-2 as a pathogen for young foals needs confirmation by further studies including experimental infection of gnotobiotic foals. A trail for evaluation of Pneumabort-K (an EHV-1 subtype 1 vaccine) was conducted in these foals. Animals inoculated with the vaccine at the age of 30 and 60 days failed to respond serologically to the immunization, and it was assumed that this was due to the intereference of the high levels of passively acquired antibody. Based on this observation, another EHV-1 vaccination procedure for foals commencing at 80-90 days was recommended.Item Epidemiological investigations of the New Zealand horse population and the control of equine influenza : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Epidemiology, Massey University, Palmerston North, New Zealand(Massey University, 2012) Rosanowski, Sarah MargaretThe aim of this thesis was to develop a disease model to evaluate the effectiveness of movement restriction and vaccination for the control of equine influenza in the New Zealand horse population. In order to achieve this aim, a series of epidemiological investigations into the characteristics, movement behaviour and biosecurity practices of the New Zealand horse population were conducted. The New Zealand equine population has never experienced an outbreak of the highly infectious, respiratory virus, equine influenza (EI). As such, New Zealand horses are naїve to the virus and completely susceptible to infection. Disease models are one tool that can be used to examine the effectiveness of control strategies and can be used to initiate informed discussion regarding potential control options. In order to develop an EI InterSpread plus model, data were required regarding the New Zealand equine population. Data were collected via cross-sectional survey regarding the non-commercial horse population, through face-to-face interviews with stud managers and through the analysis of data regarding race meetings. Properties keeping horses for competition, recreation or racing were more likely to report a movement event than properties that did not. Movement events and the frequency of movement increased with increasing numbers of mares and stallions on a stud farm and with the presence of a shuttle stallion. There were significant differences between Standardbreds and Thoroughbreds travelling to race meetings and horses travelled further to attend premier race meetings. The level of biosecurity practiced was low and unlikely to be effective at preventing EI transmission during an outbreak. The disease model investigated three vaccination strategies in conjunction with movement restriction, compared to movement restriction alone. Additionally, the timeliness of vaccination strategies and enhanced surveillance were investigated. The results of the InterSpread plus model showed that the predicted length of an EI epidemic and the number of properties infected were fewer, if vaccination was implemented. The vaccination strategy that predicted the fewest number of infected properties, and the shortest epidemic duration, was implemented on day seven after official detection at a three kilometre radius around an infected property. This thesis highlights the complexity inherent in developing disease models to support decision making.Item Copper nutrition in pasture-fed New Zealand thoroughbreds, and its role in developmental orthopaedic disease : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand(Massey University, 1997) Pearce, Simon George; Pearce, Simon GeorgeThis thesis reports studies to test the hypothesis that "dietary supplementation of pasture-fed New Zealand Thoroughbreds with copper will reduce the incidence and severity of developmental orthopaedic disease". Thoroughbred foals were raised based on New Zealand Thoroughbred industry standards at AgResearch's Equine Research Stud. Thus the first stage required the development of methods to define indices of copper status and growth plate development. Techniques were developed and evaluated for in vivo sampling of liver from the mare and neonatal foal and the distal radial physis of the neonatal foal. Pregnant Thoroughbred mares (n=24) were divided into either copper supplemented or control groups. Live foals born to each group of mares were also divided into copper supplemented or control groups. Supplementation was administered orally with aqueous copper sulphate at a rate of 0.5 mg Cu/kg liveweight (LW), and controls received a placebo of equivalent fluid volume. Mares were supplemented for the final 13 to 25 weeks of gestation until parturition. Foals were supplemented from 21 days of age with 0.2 mg Cu/kg LW increasing to 0.5 mg Cu/kg LW by 49 days remaining at that level until euthanasia at approximately 150 days. All animals grazed tall fescue pasture containing 4.4 to 8.6 mg Cu/kg dry matter (DM) for the duration of the experiment. This experimental design allowed independent investigation of both the effect of mare treatment during gestation and foal treatment on the evidence of developmental orthopaedic disease in the foals. Randomisation was stratified based on mare age, sire of the foal, last date of service and in the case of the foals only, sex of the foal. Indices of copper status were measured in both the mares and foals throughout the experiment, and at postmortem. The foals were examined regularly for evidence of developmental orthopaedic disease (DOD) which included clinical, conformational and radiological examinations. At euthanasia, an exhaustive postmortem examination was performed which included investigation of all limb and cervical spine articulations, and examination of the physes from the proximal humerus, proximal and distal radius and tibia, and distal femur, third metacarpus and third metatarsus. Physes were examined after cutting bone ends into slabs of approximately 6 mm widths using a bone saw. All abnormalities in cartilage or bone found at postmortem were submitted for histological examination. A histomorphometric study was also performed on the growth plate and metaphyseal primary spongiosa of standard sections cut through the distal radius. Plasma copper concentration of mares declined throughout the final trimester, and was not affected by copper supplementation. There was a trend toward increased copper concentration in the livers of supplemented mares, and a significant increase in the liver copper concentration of foals born to supplemented mares as determined by liver biopsies of mares and foals shortly after parturition,. Plasma and blood cell copper concentration, and plasma caeruloplasmin oxidase activity in the foals were not affected by copper supplementation, but liver copper concentration was significantly greater in copper-supplemented foals compared with controls. There was no effect of copper supplementation on the evidence of DOD in vivo, in the physes examined at postmortem, or on the histomorphometry in the distal radius. However there was an effect of mare supplementation during gestation on indices of physitis in the foals assessed from postmortem radiographs and on mild abnormalities found in the articulations of foal limbs. Copper supplementation of the foal had no effect on these indices. The low incidence and severity of lesions found in foals grazing a pasture based diet containing 4.4 to 8.6 mg Cu/kg DM, combined with the failure to demonstrate an effect of foal copper supplementation on the evidence of DOD is contrary to published and anecdotal reports within New Zealand and internationally. This prompted the investigation of a possible dietary constituents which may affect the requirement for copper. Molybdenum was identified as a possible antagonist which under certain circumstances may be found in high concentrations in a pasture diet. A pasture was prepared containing 8 to 15 mg Mo/kg DM. Weanlings were grazed on this pasture for 70 days and then supplemented with oral copper sulphate at a rate of 1.0 mg Cu/kg DM for a further 14 days (84 days total). There was no effect of high dietary molybdenum on plasma copper, trichloroacetic acid insoluble plasma copper, or blood cell copper concentration, or on the activities of caeruloplasmin oxidase or red blood cell superoxide dismutase. There was also no effect of dietary molybdenum on the liver copper concentration after 70 or 84 days. It was therefore concluded that at concentrations that might be expected in a pasture diet molybdenum is unlikely to increase copper requirements of horses. The possible implications of this work to the New Zealand Thoroughbred industry, and suggestions for further research are discussed.Item Equine respiratory viruses in New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Turitea, Palmerston North, New Zealand(Massey University, 1999) Dunowska, Magdalena; Dunowska, MagdalenaEquine respiratory disease is a cause of wastage resulting in financial losses for the equine industry throughout the world. A serological and virological survey was conducted on samples collected from a total of 133 horses from different parts in New Zealand. Three groups of foals were sampled on a monthly basis, five outbreaks of respiratory disease were investigated, and samples were collected from 37 yearlings during and following the yearling sales. The only viruses isolated were equine herpesviruses (EHV) types 2, 5, and 4. EHV-2 was isolated from 99% of peripheral blood leucocyte (PBL) samples from foals sampled on a monthly basis and from PBL of 96% of horses from outbreaks and yearlings from the sales. Additionally, EHV-2, EHV-5 or both were isolated from nasal swabs of up to 100% of foals sampled on a monthly basis between March and July. The time of virus excretion from the nasal cavity varied slightly between the three groups. The rate of virus isolation from the nasal swabs was highest at the time when most foals from two of the groups experienced some respiratory signs. Foals from the remaining group, however, were healthy throughout the study period. Of horses from outbreaks and yearlings from the yearling sales, EHV-2, EHV-5, or both were isolated from nasal swabs of 35% of horses showing respiratory signs, 9.5% of healthy horses, and 37.5% of horses for which individual clinical data were not available. EHV-4 was isolated on only one occasion, from PBL of a foal with respiratory disease. There was serological evidence that EHV-1, equine adenovirus-1 (EAdV-1), and equine rhinoviruses (ERhV) types 1 and 2 are all present in New Zealand. The average antibody seroprevalence to these viruses was 67%, 61%, 78%, and 13%, respectively. All serum samples tested were negative for antibodies to equine arteritis virus, mammalian reovirus-3 and parainfluenza virus-3. Most of the foals sampled showed serological evidence of infection with EHV-1/4 (78%), EAdV-1 (61%), and ERhV-2 (65%) within their first year of life. There was no indication that any of the foals sampled became infected with ERhV-1 within the period of study. Samples for virus isolation and two blood samples for serology were collected from 54 of 82 (66%) horses sampled from outbreaks and yearlings from the sales for which individual clinical data were available. These included 35 horses showing signs of respiratory disease around the time of sampling and 19 healthy horses. For the remaining 28 horses, either individual clinical data were not available, or the second blood sample for serology was not collected. Recent viral infection was not associated with development of respiratory signs in yearlings from the sales when all viruses were considered, although this result was not statistically significant (adjusted OR 1.3, p = 0.5). Equine herpesvirus-2/5 and ERhV-2 infections appeared to be associated with development of clinical signs in yearlings from the yearling sales, although these results were significant only for EHV-2/5, and not ERhV-2. However, since none of the foals or horses sampled was examined endoscopically, it is possible that a number of lower airway infections were not recognised. The most common infection among horses with respiratory signs from outbreaks, for which paired serum samples were available, was EHV-2/5 infection (30.4%), followed by ERhV-2 (13.0%), ERhV-1 (4.3%), and EHV-1/4 (4.3%) infections. None of the 56 horses for which a full set of data were available showed serological evidence of recent EAdV-1 infection and only two horses showed serological evidence of recent ERhV-1 infection. Most horses with signs of respiratory disease that showed serological evidence of recent viral infection also yielded EHV-2 or EHV-5 from their nasal swabs, indicating that EHV-2/5 either predisposes to other infections, or that infection with other viruses re-activates latent EHV-2/5. During the survey, EHV-5 was isolated on 56 occasions. This represented the first isolation of this virus outside Australia. Representative New Zealand isolates were compared to the reference Australian strain by restriction digest of the cloned glycoprotein B gene. Restriction fragment length polymorphism (RFLP) profiles of all but one New Zealand isolate differed from the RFLP pattern of the prototype strain. With few exceptions, isolates from different horses showed different RFLP profiles. However, isolates from individual horses, collected either at different times, from different sites, or grown on different cells showed identical RFLP patterns. The effect of EHV-2 infection on gene expression in equine leucocytes was investigated by representational difference analysis of cDNA. The results suggested that EHV-2 infection of leucocytes down-regulates the expression of monocyte chemoattractant protein-1. This indicates that EHV-2 has the ability to modulate the chemokine environment of infected cells and may predispose to secondary infections. This work has contributed to the understanding of factors involved in equine respiratory disease in New Zealand. Although infection with none of the viruses was detected only in horses showing respiratory signs, the results suggest that EHV-2/5 and equine rhinoviruses may be more important than previously thought.