Veterinary Science Collected Works - Theses
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ItemSouth-west Victorian dairy herd gastrointestinal parasite prevalence study( 2022)It is widely accepted that healthy adult cattle are generally not affected by worm burdens. However, the stress of intensive dairy situations globally has been thought to reduce cows’ immunity to gastrointestinal parasites and subsequently allow milk production losses due to these parasite burdens. Numerous global studies have indicated production benefits to anthelmintic use in lactating dairy cattle, but there have also been several publications showing marginal or no significant milk production benefit following anthelmintic use. Anthelmintic resistance has been illustrated in multiple studies and is likely to be reducing the overall production benefit seen with anthelmintic use. In adult cattle our gastrointestinal parasite measurement systems are largely flawed or insensitive. The aim of this project was to assess the use of highly sensitive faecal egg counts (FEC) to document the gastrointestinal worm burden of lactating dairy cows in south-west Victoria. We also aimed to investigate the relationship between farm management, previous anthelmintic use, milk production, faecal egg count and bulk milk anti-O. ostertagi antibody ELISA optical density ratio (ODR) testing in this region. Sensitive FECs from individual recently calved adult dairy cows were obtained through use of a modified Mini-FLOTAC procedure achieving an analytical sensitivity of 2.5 eggs per gram of faeces (epg). Individual faecal egg counts were collected on 18 farms from cohorts of primiparous and multiparous recently calved cows. Vat milk was also collected on the day of faecal sampling for laboratory assessment of ODR. Milk production data was available from 10/18 farms providing 247 individual milk production records. Faecal egg counts greater than or equal to 2.5 epg were much more likely to be recorded in primiparous cows (45%) than in multiparous cows (26%). Multiparous cows with a body condition score of < 4 were significantly more likely to have a positive FEC when compared with higher conditioned multiparous cows (p=0.002). O. ostertagi was the most abundant gastrointestinal species amongst all cohorts on all farms making up 85% of overall larvae cultured. ODR was not related to mean FEC on corresponding farms, nor was it related to the proportion of individual animals with a FEC greater than or equal to 2.5, 5 or 10 epg. ODR was strongly related to the interval, in days, between calving and prior anthelmintic use. Milk production data was analysed for the first 100 days of lactation and was divided into two groups: primiparous and multiparous. The primiparous cohort had a much higher proportion of animals with FEC greater than or equal to 2.5epg and produced on average 29% less milk than the multiparous cohort, subsequently the primiparous and multiparous groups were analysed separately. Across both primiparous and multiparous data sets, we did not observe a difference in the milk production of FEC positive or negative cows at various cut point thresholds (2.5, 5 or 10 epg. Great variation across farms was seen with milk production, when data was arranged into quartiles, based on production relative to peers on each farm, we did not observe a relationship between FEC and milk production. Mini-FLOTAC and sensitive FECs are successful in identifying adult cattle with worm burdens, but the application of these tests requires further investigation to make treatment or management guidelines. ODR should not be used as a sole decision-making tool in assessment of the requirement for anthelmintic use in pasture based dairy cattle of south-west Victoria. We did not find a difference in milk production of cows with and without FECs at 2.5 or 10 epg, because of these findings we would not suggest that FEC is useful in differentiating animals that may or may not benefit from anthelmintic treatment. Further work is required to establish a means to select individual cows for beneficial anthelmintic treatment.