The Effect of Levothyroxine Treatment on Resting Energy Expenditure of Hypothyroid Dogs

Thirty adult, client-owned dogs were diagnosed with hypothyroidism based on history, physical examination findings, hematologic and biochemical abnormalities, thyrotropin (TSH) response testing, endogenous canine thyrotropin (cTSH) concentration, or both, and total serum thryoxine concentration. All dogs received levothyroxine (L-thyroxine) at an initial dose of 22 μg/kg PO sid in either a tablet (13 dogs) or chewable form (17 dogs). Energy expenditure of each dog during apparent rest was estimated with an open-flow indirect calorimetry system by determining the rates of carbon dioxide production and oxygen consumption. Energy expenditure of apparent rest (EE) was lower in untreated hypothyroid dogs compared with reference values for EE. After treatment with L-thyroxine, EE of the hypothyroid dogs was significantly ( P < .05) higher than pretreatment values.     

A survey of feeding,management and faecal pH of Thoroughbred racehorses in the North Island of New Zealand

AIM: To identify feeding and management variables associated with variation in faecal pH within a population of intensively managed Thoroughbred racehorses in New Zealand.

METHODS: A cross-sectional survey was conducted of 16 racehorse trainers in the North Island of New Zealand. Interviews were conducted at the trainers' stables to obtain information on feeding and management of horses, and faecal samples were collected and faecal pH measured.

RESULTS: Ninety-seven percent of the horses surveyed were confined in an area ≤5 × 5 m for ≥12 h/day. Trainer's age, number of years they had trained horses, age and gender of horses, weeks in race training, racing class, frequency of feeding, bedding type, and exercise workload had no effect on mean faecal pH. Acidic faecal pH (pH ≤6.32) was associated with stables with ≤12 horses, and trainers at stables with ≤12 horses offered more concentrate feed than those at stables with >12 horses. Acidic faecal pH was associated with trainers who offered 4 kg of grain as the only form of concentrate fed, or offered ≤2.25 kg hay/day. Horses that displayed stable vices had less acidic faecal pH than horses that did not display stable vices, viz pH 6.70 (standard error of the mean (SEM) 0.135) vs 6.43 (SEM 0.029) (p=0.04).

CONCLUSIONS AND CLINICAL RELEVANCE: Racehorse management in New Zealand is similar to that observed in other major racing countries. Trainers with ≤12 horses fed more concentrates and their horses had lower faecal pH than those of trainers with >12 horses. Irrespective of management system, it appears important to provide at least 2.25 kg of hay/day ad libitum, to buffer hindgut acidosis associated with diets high in soluble carbohydrate.     

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 3. In vivo ultrasonographic assessment of the cross-sectional area and echogenicity of the superficial digital flexor tendon

AIM: To determine if the superficial digital flexor tendon (SDFT) of young Thoroughbred horses changed in size and echogenicity in association with early race training.

METHODS: Cross-sectional area (CSA) and echogenicity were determined ultrasonographically at five levels of the SDFT of the forelimbs of 2-year-old fillies (n=14), corresponding to 4, 8, 12, 16 and 20 cm distal to the accessory carpal bone (DACB). Measurements were made before and after a 13-week period in which a trained group of seven horses was compared with another group of seven untrained horses.

RESULTS: Level below the accessory carpal bone had a significant effect on CSA and Level 8 was smaller than all other levels except Level 12, while Level 12 was smaller than Levels 4 and 20 but not different from Levels 8 and 16. There was a significant interaction between level and time due to effects observed at Level 8. The CSA at Level 8 measured pre-training was different from that of Levels 4 and 20 in both pre- and post-training groups (p<0.05), but when measured post-training was not different from any other measurement. There was also a significant interaction between treatment group and time. There was no difference between CSA for the untrained and trained groups at the pre-training observation (p=0.9), but post-training the CSA (pooled over all levels) in trained horses was significantly larger than that of the untrained horses both post-training (p=0.019) and pre-training (p=0.034), and was not different from the pretraining CSA recorded in the trained group (p=0.29). Treatment group had no effect on echogenicity (p=0.43), while echogenicity was less at the end of the trial in both trained and untrained horses (p<0.001).

CONCLUSIONS: Early training for racing was associated with an increase in mean CSA of the SDFT. Other factors such as age and maturity may play a role in limiting this increase.     

Musculoskeletal responses of 2-year-old Thoroughbred horses to early training. 1. Study design,and clinical,nutritional, radiological and histological observations

AIMS: This is the first in a series of papers reporting studies in 2-year-old Thoroughbred racehorses that aimed to determine the response of musculoskeletal tissues to early training on grass and sand racetracks. In this paper, the experimental set-up of the whole study is described, and nutritional, workload, and clinical, radiographic and pathological outcomes are reported, including semi-quantitative assessment of macroscopic changes in articular cartilage.

METHODS: The study group comprised 14 two-year-old Thoroughbred fillies reared entirely at pasture. Of these, seven were selected by a licensed racehorse trainer to undergo a 4-week period of initial training in which they were taught to accept saddle and rider, followed by a 13-week period of flatrace training at a racetrack (Weeks 1–13); the other seven fillies were confined to large grass enclosures and were not trained. Nutrient, including macro- and trace-element intakes were estimated. Distances cantered or galloped and average velocities were quantified for the trained horses. All horses were observed daily, weighed approximately weekly, and underwent a clinical lameness examination at Weeks 5, 9 and 13. Distal forelimbs were radiographed prior to Week 1, during Weeks 7–8, and again at the end of the study, when macroscopic changes in articular cartilage of the proximal surface of the proximal phalanx were also scored after staining with India ink.

RESULTS: Dietary intakes met or exceeded recommended requirements for all nutrients except sodium, which was low in the trained horses. Bodyweight increased throughout the study in the untrained horses, and increased until Week 7 and then decreased slightly in the trained horses. Mean velocity data were used to define three stages of the training programme: Stage 1 comprised canter in Weeks 1–4; Stage 2 comprised canter in Weeks 5–8; and Stage 3 comprised canter in Weeks 9–13 and galloping twice weekly. Four of seven horses completed training. These covered a mean distance of 179.2 km at mean velocities (excluding gallops) of 7.63 m/sec (SD 0.58), 8.99 m/sec (SD 0.56), and 8.43 m/sec (SD 0.74) for Stages 1–3, respectively, and galloped 4.45 km at 14.4 (SD 0.1) m/sec. The three horses that did not complete training became lame in Weeks 9, 10 and 11, and covered 147.9 km at velocities of 7.38 m/sec (SD 0.44), 8.88 m/sec (SD 0.33) and 8.43 m/sec (SD 0.59) and galloped 2.1 km. Overall, slight or intermittent lameness in trained horses was noted on 76/655 (12%) of horse observation days. Swelling was evident on 284/655 (41%) of horse observation days in the metacarpophalangeal (MCPJ) and metatarsophalangeal (MTPJ) joints (92%), palmar metacarpal tendon region (7%) or carpus (1%). Swelling of the MCPJ or MTPJ was not associated with obvious lameness. Radiographic changes were minor and no gross lesions in bone or tendon tissue were evident except for one case of dorsal metacarpal disease. Post mortem, the cartilage of some MCPJ and MTPJ had obvious wear lines and high lesion scores, which were not consistently related to clinical evidence of pain, lameness or joint swelling. Mean lesion scores were not significantly different between the MCPJ and MTPJ, or between trained and untrained horses.

CONCLUSIONS: Workload can be readily quantified in racehorses under semi-commercial training conditions. Obvious lesions in cartilage of the MCPJ or MTPJ were present in some trained and some untrained horses and not consistently associated with clinical evidence of lameness, joint swelling or change in other connective tissues.

CLINICAL RELEVANCE: Workload data in racing horses are likely to be highly relevant for studying the pathogenesis of changes in bone, tendon and cartilage during training, for training management and for risk analysis in racehorse populations. Although obvious cartilage lesions produced little clinical effect, such lesions have previously been shown to be progressive and to prejudice athletic capability. Detection of such occult lesions in young horses will require more sophisticated detection methods.     

Genetic structure of Fusarium pseudograminearum populations from the Australian grain belt

Crown rot, caused by the fungus Fusarium pseudograminearum (teleomorph Gibberella coronicola) is a major disease of wheat in the Australian grain belt. However, there is little information available on the population structure of this pathogen. We measured genetic diversity as assessed with amplified fragment length polymorphism (AFLP) analysis within and between populations of F. pseudograminearum from northeastern, south central, and southwestern regions of the Australian grain belt. Amongst the 217 isolates, 176 haplotypes were identified and grouped into two main clusters. One cluster contained isolates from populations in northeastern Australia, and the other cluster contained isolates from populations in south central and southwestern Australia. The southern populations were distinguished from the northeastern populations by higher levels of population differentiation (Gst) between them and genetic identity amongst the regional populations. We hypothesize that the F. pseudograminearum populations from northeastern and southern Australia are independent, which could result from different founding events or from geographic isolation and the accumulation of genetic differences due to genetic drift and/or selection.     

Limited morphological,physiological and genetic diversity of Phytophthora palmivora from cocoa in Papua New Guinea

In Papua New Guinea (PNG) cocoa (Theobroma cacao) is one of the most important cash crops grown in the tropical lowland and island regions. As in most cocoa‐growing areas, phytophthora black pod and canker cause significant yield losses. Cocoa breeding activities in PNG are focused in East New Britain province where disease control recommendations are also developed. This study tested the hypothesis that there was no diversity in the Phytophthora palmivora population causing black pod on cocoa by characterizing the variation in pathogen populations within and between the five major cocoa‐growing areas. Diseased pods were sampled hierarchically from the five locations and additional isolates were collected from soil, stem and leaf lesions, or retrieved from culture collections. Morphological characters showed continuous variation within the range described for P. palmivora. Genetic analysis revealed that the isolates belonged to one dominant clonal lineage, with restricted distributions of several other subpopulations. Lowest diversities were found in the geographically isolated Karkar Island and East Sepik province. Soil isolates showed greater genetic diversity than isolates from cocoa lesions. Intra‐farm variation was as much as inter‐farm or inter‐province variation. Both mating types were detected, although no strong evidence of sexual recombination was observed. The analysis revealed limited geographic, temporal or host specialization, suggesting continuous selection for pathogenicity from a genetic pool of P. palmivora. These findings have significant implications on the deployment of cocoa genotypes, enforcement of inter‐province quarantine and sustainable disease management strategies.     

Fusarium oxysporum f. sp. radicis‐vanillae is the causal agent of root and stem rot of vanilla

Root and stem rot (RSR) is a very detrimental disease of vanilla worldwide. Fusarium oxysporum is frequently associated with the disease but other Fusarium species are also reported. In this international study, 52 vanilla plots were surveyed in three of the most important vanilla producing countries (Madagascar, Reunion Island and French Polynesia) in order to determine the aetiology of RSR disease. Subsets from the 377 single‐spored Fusarium isolates recovered from rotten roots and stems in the surveys were characterized by molecular genotyping (EF1α and IGS gene sequences) and pathogenicity assays on Vanilla planifolia and V. ×tahitensis, the two commercially grown vanilla species. Fusarium oxysporum was shown to be the principal species responsible for the disease, representing 79% of the isolates recovered from the RSR tissues, 40% of which induced severe symptoms on inoculated plantlets. Fusarium oxysporum isolates were highly polyphyletic regardless of geographic origin or pathogenicity. Fusarium solani, found in 15% of the samples and inducing only mild symptoms on plantlets, was considered a secondary pathogen of vanilla. Three additional Fusarium species were occasionally isolated in the study (F. proliferatum, F. concentricum and F. mangiferae) but were nonpathogenic. Histopathological preparations observed in wide field and multiphoton microscopy showed that F. oxysporum penetrated the root hair region of roots, then invaded the cortical cells where it induced necrosis in both V. planifolia and V. ×tahitensis. The hyphae never invaded the root vascular system up to 9 days post‐inoculation. As a whole, the data demonstrated that RSR of vanilla is present worldwide and that its causal agent should be named F. oxysporum f. sp. radicis‐vanillae.