Bovine leukemia virus (BLV) causes enzootic bovine leukosis and can lead to significant economic losses in dairy herds. Accurate estimation of within-herd prevalence is an essential step for effective continuous surveillance and control. The objectives of this study were: (1) to build a statistical model predicting within-herd BLV prevalence using Bulk Tank Milk (BTM) ELISA antibody titers, (2) to assess the temporal stability of this model over three years, and (3) to explore the relationship between mean individual cow antibody titers and BTM results. A convenience sample of 30 dairy herds in the Canadian Maritimes was studied. Three years of bi-monthly BTM samples were collected to measure the BTM ELISA antibody titers. Individual ELISA testing of cows contributing to BTM was performed annually for three years, permitting estimation of the true within-herd prevalence. Among the 30 herds, 1453 cows tested BLV-positive in Year 1, 899 in Year 2, and 760 in Year 3. Mean within-herd prevalence were 42 % (SD 24 %), 31 % (SD 20 %), and 29 % (SD 20 %) in Year 1, 2, and 3, respectively. Seven univariable linear regression models for true within-herd prevalence were built, with predictors consisting of single BTM results or averages from two or three rounds of BTM results in proximity to the time of individual ELISA testing. The model using the average of two BTM samples collected two months apart as a predictor prevalence in the herd was selected as the best model based on the highest R² = 0.91 and Predictive R² = 0.90. Model predictions showed strong agreement with observed within-herd prevalence in subsequent years (concordance correlation coefficients 0.94-0.98), indicating temporal stability. Mean individual cow antibody titers were strongly correlated with BTM antibody levels (r = 0.95). This study presents a practical, stable, and cost-effective approach to estimate and monitor BLV within-herd prevalence using BTM ELISA testing. The model can support surveillance programs and help guide herd-level BLV management decisions over time.

Bovine leukemia virus causes enzootic bovine leukosis, the most common neoplastic disease of dairy cattle worldwide. Infection is lifelong, with most cattle remaining asymptomatic, approximately one-third developing persistent lymphocytosis, and a small proportion progressing to lymphoma. The proviral load (PVL), measured as the number of provirus copies per estimated white blood cell, is an indicator of transmission risk and disease progression and can be used to identify animals that contribute most to virus spread in control programs. However, longitudinal data describing PVL dynamics at the individual cow level are limited. The objectives of this study were to quantify temporal changes in PVL in naturally infected dairy cows over 3 years and evaluate the implications for repeated PVL testing in BLV control programs. A total of 716 BLV-positive cows from 25 commercial dairy herds in the Canadian Maritime provinces (Prince Edward Island, Nova Scotia, and New Brunswick) were included. Cows underwent annual PVL testing using quantitative PCR and were categorized as high, moderate, low, or undetectable PVL. Temporal changes in PVL were evaluated using repeated measurements, and conversion between PVL categories was assessed over one- and 2-year intervals. BLV proviral load showed an overall temporal trend toward higher values, with corresponding shifts in PVL categories observed across initial classification groups and within individual animals. Of cows with an initial low-PVL, 12% progressed to high-PVL over the study period. Among cows initially classified as moderate-PVL, 53% transitioned to high-PVL. A subset of cows maintained undetectable-PVL despite confirmed BLV seropositivity. These findings indicate that the likelihood of PVL progression is influenced by the initial PVL category, with moderate-PVL cows representing the group at greatest risk of becoming highly infectious. The results have practical implications for BLV control programs in dairy herds. Repeated PVL testing of cows with moderate-PVL may help identify animals at increased risk of viral transmission and guide targeted culling or segregation decisions. In contrast, cows with low-PVL may require less frequent testing, and cows with persistently undetectable-PVL may not require repeated PVL monitoring. Tailoring PVL testing frequency according to initial PVL status may improve the efficiency of BLV control programs by prioritizing management of highly infectious animals and reducing herd-level virus transmission.

Summary Background Apical proximal sesamoid bone (PSB) fractures are a common occurrence in Standardbred racehorses due to the high‐intensity nature of their work. Several studies have evaluated the racing performance after surgical removal of apical fracture fragments in Thoroughbred horses, however information pertaining to Standardbred racehorses is limited. Objectives To (i) describe the distribution of apical PSB fractures in a population of Standardbred racehorses; and (ii) measure return to athletic ability in these horses following surgical removal of apical PSB fracture fragments. Study design Retrospective. Methods Medical records of Standardbred racehorses presenting to the Atlantic Veterinary College (AVC) for surgical treatment of an apical PSB fracture were reviewed. Lifetime racing records were obtained, and the five race starts before injury and the five race starts following surgical treatment were analysed for total earnings and number of top‐3 placings for each horse. Results Thirty‐three horses raced following surgery; 22 of which were racing prior to injury. No significant differences were found in top‐3 placings or monetary earnings for the 22 horses which had raced prior to and after surgery. There was no significant difference in limb or sesamoid affected and return to racing. No associations were found between type of surgery performed or degree of suspensory desmitis and whether the horse returned to racing. Main limitations Small sample size. Conclusions 88% of horses that were racing prior to injury also raced following surgical treatment of an apical PSB fracture. Surgical removal of apical PSB fractures in Standardbred racehorses does not appear to affect their future athletic ability.

Objective:For horses presenting for colic to a referral hospital in Atlantic Canada, we aimed to describe clinical findings, diagnosis, treatment, and outcome for draft breeds; identify associations between clinical findings, diagnosis, treatment, and outcome for draft compared to nondraft breeds; and identify the overall impact of draft breed on mortality. Methods:A retrospective review of equine colic cases presenting to the Atlantic Veterinary College (2004 to 2023). Logistic regression models were used to assess associations between parameters and draft breed and mortality. Results:A total of 721 horse colic events were included in the study; 68 (9.4%) were categorized as draft breeds. Among draft breeds, large intestine nonstrangulating obstruction was the most frequent diagnosis (30.9%), followed by GI-related medical (23.5%) and open (19.1%). Draft breeds did not significantly differ from nondraft breeds in the type of management received (medical or surgical). At admission, draft breeds were significantly more likely to have an increased heart rate and elevated abdominal protein, peripheral lactate, total protein, and fibrinogen concentrations. Fifty-nine percent of draft breed cases survived until discharge. In multivariable analysis, draft breeds did not significantly differ from nondraft breeds in survival. Conclusions:Although draft breeds presenting with colic were more likely than nondraft breeds to present with variables associated with nonsurvival, draft breed status was not an overall predictor for nonsurvival at this referral institution. Clinical Relevance:This study describes the clinical findings, diagnosis, treatment, and outcomes for draft breeds experiencing colic at a referral institution. Draft breed status was not a predictor for nonsurvival.

IntroductionBovine Leukemia Virus (BLV) prevalence remains high in dairy cattle in North America. Quantifying the proviral load (PVL) in BLV-positive cows can be used to control this disease in herds where BLV is prevalent by focusing culling of high PVL animals to reduce the risk of transmission. The impact of high BLV PVL on dairy cows’ performance is not well established. The objective of this study was to assess the effect of high PVL status on milk production, occurrence of subclinical ketosis or mastitis, or fertility in BLV-infected cows.MethodsTwenty-five herds from the three Maritime provinces in Atlantic Canada were enrolled in this study. BLV infected cows were first identified by individual milk or serum testing. A validated quantitative qPCR was used to quantify the PVL in cows with positive BLV antibody results. Parity, 305-day milk production, annual geometric average somatic cell count, fat-to-protein ratio in milk on the first test post-calving, days in milk at first service, and calving-to-conception interval were collected from DairyComp305 software. Two-level mixed multivariable regression models were used to assess the relationship between BLV PVL and milk production, subclinical mastitis and ketosis and reproduction performance.ResultsHigh PVL was strongly associated with reduced milk production (387 kg and 431 kg) and reproduction performance (calving-to-conception interval lengthened by 50 days and 49 days), and higher odds of subclinical mastitis (Odds ratio = 2.38 and 2.48), when compared to BLVpositive cows with a low PVL and BLV-negative cows, respectively.ConclusionThese results support implementing a control program to prioritize culling high PVL cows.

Objective The primary objective was to determine the youngest age group where bovine leukemia virus (BLV)-infected dairy animals were identified. The secondary objective was to investigate associations between age-specific management practices and BLV infection status of different age groups of dairy calves and heifers. Procedure For enrolled herds, BLV status was determined using blood samples from pre-weaned calves, weaned calves, and breeding-age heifers; and bulk tank milk from the adult herd. A questionnaire investigating age-specific management factors was administered for each herd. Ordinal logistic regression was performed to identify management factors associated with the youngest age range in which BLV was identified. Results Fifty-three dairy herds from the 4 provinces in Atlantic Canada were enrolled. Bovine leukemia virus was most commonly earliest identified in pre-weaned heifers (18 herds, 32.1%) and the adult herd (18 herds, 32.1%). Ordinal logistic regression revealed that BLV was first identified in older age groups more often than in younger age groups when herds regrouped weaned heifers at least once, when fly control was used for breeding-age heifers, when herds practiced foot trimming on breeding-age heifers, and when bred heifers were brought in. Conclusion Producers can use results to identify the youngest age group(s) in which BLV is identified and to tailor management strategies to prevent new infections.

Background This study aimed to describe and compare therapeutic approaches for horses with acute diarrhea in different geographic regions worldwide. Methods Clinical information was retrospectively collected from diarrheic horses presented to participating institutions between 2016 and 2020, including fluid therapy on admission, antimicrobial drugs, probiotics, anti-endotoxic medications, anti-inflammatory drugs, gastroprotectants, digital cryotherapy, and toxin-binding agents. Seasonal and geographic differences were investigated. Results 1438 horses from 26 participating hospitals from 5 continents were included. On admission, 65% (926/1419) of horses were administered a fluid bolus. Antimicrobial drugs were administered to 55% (792/1419) within the first 24 hours of admission, with penicillin and gentamicin being the most used combination (25%, 198/792). Horses with leukopenia (OR: 2.264, 95%CI: 1.754 to 2.921; P<0.001) or meeting systemic inflammatory response syndrome criteria (OR: 2.542, 95%CI: 1.919 to 3.368; P<0.001) had higher odds of being administered antimicrobial drugs. Other treatments administered included probiotics (15%, 215/1438), polymyxin B (13%; 187/1438), pentoxifylline (8%; 118/1438), gastroprotectants (44%; 626/1419), digital cryotherapy (34%; 489/1435), plasma transfusion (13%; 182/1410) and toxin-binding agents (36%; 515/1438). Limitations Due to the retrospective nature of the study, the rationale for treatment decisions was unavailable, and associations with survival could not be evaluated. Conclusions Treatments varied between hospitals from different geographic regions. Prospective clinical trials are required to evaluate the effects of various treatments on survival.

Respiratory disease is common in the horse population and is often be associated with poor performance in equine athletes. Despite their outstanding strength and aerobic capacity, little regard is given to draft horses and the respiratory disorders they may encounter when performing athletic activity. For this reason, the objectives of this study were: (1) to determine the prevalence of exercise-induced pulmonary hemorrhage (EIPH), tracheal mucus (TM) and recurrent laryngeal hemiplegia (RLH) in a population of competitive draft pulling horses, and (2) to determine if there was an association between horse weight, height, age, amount pulled, or competition placing with EIPH or laryngeal disorders in draft pullers. Results of this study identified EIPH in 26% of the study population, RLH in 32% and TM in 82% of participating horses; however, no risk factors were identified for the development of these problems in draft pulling horses

Two equine patients presented separately with severe abdominal distention, colic, lethargy, and decreased appetite. An ante-mortem diagnosis of lymphoma was reached in each case based on peritoneal fluid cytology. Due to a poor prognosis, the horses were humanely euthanized. Post-mortem examination with histology and immunohistochemistry confirmed both cases as lymphoma: alimentary B-cell lymphoma of the distal jejunum and cecum in one case, and T-cell lymphoma of the cecum in the second case. Both cases exhibited extensive metastasis with peritoneal and pleural serosae covered in small nodules and plaque like masses consistent with lymphomatosis. These cases document a unique presentation of lymphoma in equine patients presenting as peritoneal lymphomatosis with ascites.

Respiratory disease is common in the horse population and is often associated with poor performance in equine athletes. Despite their outstanding strength and aerobic capacity, little regard is given to draft horses and the respiratory disorders they may encounter when performing athletic activity. For this reason, the objectives of this study were: (1) to determine the prevalence of exercise-induced pulmonary hemorrhage (EIPH), tracheal mucus (TM) and recurrent laryngeal hemiplegia (RLH) in a population of competitive draft pulling horses, and (2) to determine if there was an association between horse weight, height, age, amount pulled, or competition placing with EIPH, TM or RLH in draft pullers. Results of this study identified EIPH in 26% of the study population, RLH in 32% and TM in 82% of participating horses; however, no risk factors were identified for the development of these problems in draft pulling horses.

Abstract Background There is currently no commercially available method in Canada to identify bovine leukemia virus (BLV)‐positive cows with high proviral load (PVL). Objectives First, develop a model to predict PVL using common, commercially available, cost‐effective diagnostic tests. Second, investigate the relationship between lymphocyte count and PVL in BLV‐positive cows. Animals A total of 339 BLV‐positive and 62 BLV‐seronegative cows on 15 dairy farms. Methods Cross‐sectional study. Blood and milk samples were collected from all lactating BLV‐positive cows on each farm and 5 to 10 BLV‐seronegative cows depending on herd size. Blood and milk samples were tested for anti‐BLV antibodies using enzyme‐linked immunosorbent assay (ELISA). Complete blood counts were performed on blood samples, and standard components analyses were obtained for milk samples. Proviral load was determined by quantitative polymerase chain reaction for each cow. Results The inverse of lymphocyte count, the square of the inverse of lymphocyte count, and milk ELISA percent positivity were positively associated with increasing PVL in BLV‐positive cows. For BLV‐positive cows, lymphocyte count >5.2 × 109/L predicted a high PVL (BLV:Bovine DNA of >1 in blood) with a sensitivity of 92.4% and a specificity of 79.8%. For BLV‐positive cows, white blood cell count >10.8 × 109/L predicted a high PVL, with a sensitivity of 85.5% and a specificity of 83.6%. Conclusions and Clinical Importance Based on these results, producers can implement commonly available diagnostic tests to identify cows with high probability of having high PVL, which may help in designing effective disease control strategies for BLV‐positive herds.

Atrial fibrillation (AF) is the most clinically relevant cardiac arrhythmia identified in the Standardbred racehorse. However, there is limited literature regarding athletic ability in Standardbred racehorses following AF conversion. To investigate this issue, the objectives of this review were to: i) determine the success rate in using quinidine sulphate to treat AF in a population of hospitalized equine patients in Atlantic Canada between January 2008 and December 2019; and ii) measure return to athletic ability (using racetrack earnings and top-3 finishes) following cardioversion with quinidine sulphate in a population of Standardbred racehorses. Overall, 73% (16/22) of AF instances in this study were successfully treated with enteral quinidine sulphate. No significant difference was detected in racetrack earnings or number of top-3 finishes for each horse that raced at least 5 times pre- and post-conversion. Key clinical message: To the authors' knowledge, this is the first published review to assess the athletic ability of Standardbred racehorses following cardioversion with enteral quinidine sulphate. Based on the current information, it does not appear that treatment of AF with quinidine sulphate affects future athletic performance in horses that achieved cardioversion.

This study describes the clinicopathological findings, diagnostic approach, treatment, and factors associated with non-survival of diarrheic horses admitted to 4 Canadian university teaching hospitals between 2015 and 2019. A total of 300 horses, ≥1-year-old, with acute diarrhea were included and represented 1.6% (300/18 481; range: 0.7 to 3%) of admissions during that period, 70% of the horses survived to discharge. Testing for enteropathogens was limited to a single fecal culture for Salmonella spp. in most cases. An enteropathogen was identified in 14% (42/300) of the horses, but in the hospital with higher testing rates enteropathogens were detected in 29% (16/55) of cases. Neorickettsia risticii was the pathogen most frequently detected (31%, 32/102). Antimicrobial drugs and plasma were administered to 57 and 8% of the cases, respectively. Laminitis occurred in 24/298 (8%) of the horses. A multivariable regression model identified an association between non-survival of diarrheic horses and colic signs, increased heart rate, packed cell volume, creatinine concentration, and decreased total protein concentration. A standardized approach for pathogen detection in diarrheic horses is not consistent among Canadian veterinary teaching hospitals, and testing for known pathogens is limited. Signs of colic, severe dehydration, endotoxemia, and hypoproteinemia are associated with non-survival of diarrheic horses.

Bulk tank milk (BTM) samples are used to determine the infection status and estimate dairy herd prevalence for bovine leukaemia virus (BLV) using an antibody ELISA assay. BLV ELISA variability between samples from the same herd or from different herds has not been investigated over long time periods. The main objective of this study was to determine the within-herd and between-herd variability of a BTM BLV ELISA assay over 1-month, 3-month, and 3-year sampling intervals. All of the Canadian Maritime region dairy herds (n = 523) that were active in 2013 and 2016 were included (83.9% and 86.9% of total herds in 2013 and 2016, respectively). BLV antibody levels were measured in three BTM samples collected at 1-month intervals in early 2013 as well as two BTM samples collected over a 3-month interval in early 2016. Random-effects models, with fixed effects for sample replicate and province and random effects for herd, were used to estimate the variability between BTM samples from the same herd and between herds for 1-month, 3-month, and 3-year sampling intervals. The majority of variability of BTM BLV ELISA results was seen between herds (1-month, 6.792 ± 0.533; 3-month, 7.806 ± 0.652; 3-year, 6.222 ± 0.528). Unexplained variance between samples from the same herd, on square-root scale, was greatest for the 3-year (0.976 ± 0.104), followed by the 1-month (0.611 ± 0.035) then the 3-month (0.557 ± 0.071) intervals. Variability of BTM antibody levels within the same herd was present but was much smaller than the variability between herds, and was greatest for the 3-year sampling interval. The 3-month sampling interval resulted in the least variability and is appropriate to use for estimating the baseline level of within-herd prevalence for BLV control programs. Knowledge of the baseline variability and within-herd prevalence can help to determine effectiveness of control programs when BTM sampling is repeated at longer intervals.

An 8-day-old alpaca was presented for suspected meconium impaction and abnormal gait and posture. Physical examination revealed bilateral medial patellar luxation. In previous reports, medical treatment of patellar luxation in crias has been associated with a poor to grave prognosis; here we report a case of successful resolution.

Congenital stationary night-blindness (CSNB) is a recessive autosomal defect in low-light vision in Appaloosa and other horse breeds. This condition has been mapped by linkage analysis to a gene coding for the Transient Receptor Potential cation channel Member 1 (TRPM1). TRPM1 is normally expressed in the ON-bipolar cells of the inner nuclear layer of the retina. Down-regulation of TRPM1 expression in CSNB results from a transposon-like insertion in intron 1 of the TRPM1 gene. Stop transcription signals in this transposon significantly reduce TRPM1 primary transcript levels in CSNB horses. This study describes additional contributions by a second mutation of the TRPM1 gene, the ECA1 108,249,293 C > T SNP, to down-regulation of transcription of the TRPM1 gene in night-blind horses. This TRPM1 SNP introduces a consensus binding site for neuro-oncological ventral antigen 1 (Nova-1) protein in the primary transcript. Nova-1 binding disrupts normal splicing signals, producing unstable, non-functional mRNA transcripts.