CASE DESCRIPTION Outbreaks of sudden death in apparently healthy weaned dairy calves due to Strongyloides papillosus parasitism were diagnosed on 2 separate and independent New York (NY) dairies. CLINICAL FINDINGS Most calves were found dead; however, 1 calf observed while dying showed signs of tachycardia, tachypnea, vocalization, and convulsions shortly before death. In 6 affected heifers that underwent post-mortem examination, precocious bilaterally symmetric mammary gland enlargement was seen. A portion of their parasitized living cohorts also demonstrated similar mammary gland enlargement. A diagnosis of S papillosus hyperinfection was made based upon the presence of high numbers of S papillosus ova in feces, and confirmation by S papillosus–specific PCR assays. Consistent histopathological findings in affected calves included generalized mammary gland vascular congestion, interstitial edema and hemorrhage with ductal hyperplasia. Mild multifocal cardiomyocyte degeneration was found in 5 of 14 calves examined. Factors believed to contribute to the parasite’s environmental amplification and host hyperinfection included group housing on wood shavings and high environmental temperatures and humidity. TREATMENT AND OUTCOME Treatment of calves with doramectin pour-on stopped mortality and resolved the udder enlargement. CLINICAL RELEVANCE Similar outbreaks have previously been described in Japan and South Bohemia (Czech Republic), where researchers hypothesized that sudden death may be due to fatal arrhythmia caused by a parasite-associated cardiotoxin. This report highlights the importance of including S papillosus among the differential diagnoses for sudden death alone or together with precocious udder enlargement in calves kept in confinement housing.
Selective dry cow therapy (SDCT) has been shown to be an effective way of using antimicrobials judiciously on dairy farms while decreasing treatment costs and maintaining herd health. However, adoption of the practice has been slow in the U.S. In order to improve the adoption of this practice in New York State, we formed a team of veterinarians to help interested dairy producers and their herd veterinarians to implement SDCT successfully. Not all farms are a good fit for SDCT. An in-depth discussion between the herd veterinarian and farm stakeholders before adoption is necessary. This discussion should include current practices, data available to make the selection process, best practices for dry off and dry-pen management, and how to monitor progress going forward. Our team enrolled 24 farms over the course of a year. Seventeen out of 24 farms are still using SDCT at the time of publishing. A variety of SDCT methods were used, and on average, herds decreased dry cow antibiotic use by 53%. The metrics we used to monitor herd infection dynamics before and after SDCT included average monthly somatic cell count, fresh cow mastitis incidence, average herd prevalence of a high first test, average herd prevalence of subclinical infection, average new infection risk, and cure risk. For all but a few herds, 95% confidence intervals overlapped for all outcomes before and after starting SDCT and differences were relatively small. In our experience, SDCT, if employed on the right farm, is an effective way to use antibiotics judiciously at dry off without disrupting herd health.
Selective dry cow therapy (SDCT) is both a cost-saving and antimicrobially conscientious approach to the critical time of dry off in a dairy cow’s lactation. Guidance regarding proper implementation is crucial to the success of a SDCT program, and farm and cow-level selection parameters should be carefully followed. The objective of this project was to create a formal program in which eligible dairy farms in New York State would receive guidance in the form of SDCT protocol development, software use, dry-off procedure training and data monitoring regarding udder health and milk quality parameters through the entire enrollment period. Here we describe the program and farm performance after implementation thus far.
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