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Anti-O.ostertagi antibody ODR in bulk tank milk assesses exposure not parasitism
Loughnan, T.; Beggs, D.; Mansell, P...
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Objective: International research has suggested that anti O. ostertagi antibody optical density ratio (ODR) of vat milk can indicate the level of milk production benefit producers will get from applying effective anthelmintic treatments to lactating dairy cows. ODR is an assessment of the magnitude of antibody production specific to O. ostertagi. In Australian pastoral dairy systems, lactating cows and young stock graze on pasture for 100% of their life and there will often be a prolonged worm season in dairy regions due to the high rainfall climate. The objective of this study was to look for a correlation between ODR and faecal egg count (FEC) or the presence of parasite eggs in faeces in corresponding cohorts.
Materials and Methods: Fourteen herds in south-west Victoria (Australia) were included in the study. All were commercial dairy enterprises. Milk vat samples were collected during the calving period for ODR. On the same day, faecal samples were collected from recently calved cows (less than 30 days in milk) for individual FEC (sensitive to 2.5 eggs per gram of faeces). Fifteen primiparous and 15 multiparous animals of representative ages were sampled. Farm practices including recent and routine anthelmintic use was recorded for each property and each cohort of animals. Data analysis was then undertaken using the Jamovi statistical package.
Results: Bulk milk ODR was not related to measurable FEC in corresponding herds. Bulk milk ODR was also not related to the proportion of animals in each corresponding co- hort with detected parasite eggs in faeces. Bulk milk ODR was strongly correlated to the number of days since most recent anthelmintic application (r2=0.73).
Conclusion: Anti-O. ostertagi ODR is a good measure of likely antibody presence against O. ostertagi. However, in pastoral systems in Australia where worms are present on pasture for sustained periods, possibly year-round, it may not be a good measure of current parasite load. ODR should not be used as the sole determinant of anthelmintic application in Victorian pastoral dairy herds.
Keywords: Australia, pasture-based, dairy, ODR, FEC.
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Affiliation of the authors at the time of publication
Colac Vet Clinic, Colac, Australia;
The University of Melbourne, Melbourne, Australia.
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