Emily John

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.

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.

Summary: Lymphoma in horses is uncommon and rarely diagnosed as a cause of ataxia. This case report describes a 2‐year‐old Standardbred cryptorchid colt who presented with acute onset of grade 3–4/5 spinal ataxia in all four limbs, with the hindlimbs more severely affected than forelimbs and severe proprioceptive deficits. Due to the severity of the ataxia, a full neurologic examination could not be completed, and the colt was humanely euthanised. Post‐mortem examination revealed multiple osteochondritis dissecans lesions in the cervical and lumbar spine. Initially, this was thought to be the cause of the ataxia; however, histopathology revealed multifocal areas where the spinal nerve roots and epidural surface of the dura mater of the meninges were surrounded or covered by plaques of neoplastic round cells which infiltrated the adipose tissue surrounding the spinal tissues. Atypical round cells similar to those observed in the spinal meningeal tissues were also found in the kidneys, lungs, liver, testes and one lymph node. Immunohistochemical staining of meningeal tissue samples revealed moderate‐to‐intense cytoplasmic/membranous immunoreactivity for CD20 and a diagnosis of multicentric diffuse large B cell lymphoma was made. These results indicate that lymphoma should be included as a differential diagnosis for a horse presenting with acute ataxia that does not have evidence of spinal cord compression, equine protozoal myeloencephalitis, equine herpesvirus‐1 myeloencephalopathy, equine degenerative myeloencephalopathy, equine motor neuron disease, trauma or other more common sources of ataxia.

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.

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.

Lymphoma in horses is uncommon and rarely diagnosed as the cause of ataxia in horses. This case report describes a two-year-old Standardbred cryptorchid colt who presented with acute onset of grade 3.5/5 ataxia. Due to the severity of the ataxia, a full neurologic examination could not be completed, and the colt was humanely euthanized. Post-mortem examination revealed multiple osteochondritis dissecans lesions in the cervical and lumbar spine. Initially this was thought to be the cause of the ataxia, however histopathology revealed multifocal areas where the spinal nerve roots and epidural surface of the dural mater of the meninges were surrounded or covered by plaques of neoplastic round cells which infiltrated the adipose tissue surrounding the spinal tissues. Atypical round cells similar to those observed in the spinal meningeal tissues were also found in the kidneys, lungs, liver, testes and one lymph node. Immunohistochemical staining of meningeal tissue samples revealed moderate to intense cytoplasmic/membranous immunoreactivity for CD20 and a diagnosis of multicentric diffuse large B cell lymphoma was made. Lymphoma should be included in the differential diagnoses for a horse presenting with ataxia and neurologic deficits

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. 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. 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. 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.

OBJECTIVE: To describe a unique presentation of systemic Listeria monocytogenes infection in a lactating adult Holstein cow. ANIMAL: 3-year-old second-parity female Holstein, 200 days in milk. CLINICAL PRESENTATION, PROGRESSION, AND PROCEDURES: A 3-year-old Holstein dairy cow was presented for decreased appetite, decreased milk production, and pyrexia. Blood work displayed marked abnormalities in liver-associated parameters. A diagnosis of L monocytogenes cholangiohepatitis was made following liver biopsy, histopathology, and bacterial culture. TREATMENT AND OUTCOME: The cow was treated with systemic antimicrobial and antipyretic therapy. The cow was discharged to continue treatment on farm, and at time of last communication with the owner, the cow was doing very well, with full resolution of clinical signs. CLINICAL RELEVANCE: This case report describes a novel presentation of L monocytogenes infection in an adult bovine. L monocytogenes cholangiohepatitis should be considered a rare differential diagnosis in cattle presenting with evidence of pyrexia and liver disease.