Faecal egg counts in Australian pasture-based dairy herds

In Australian pastoral dairy systems, a variety of 'routine' anthelmintic programs are used in lactating cows varying from nil anthelmintic use to bi-annual application. Anthelmintic resistance has been repeatedly diagnosed on dairy farms and studies have indicated variable milk production benefits from anthelmintics internationally. We aimed to identify the predominant gastrointestinal parasites in recently calved dairy cows in south-west Victoria and examined the relationship between individual faecal egg counts (FEC) and other cow and management factors such as body condition score, age, and historical anthelmintic use. This study included 18 pasture-based dairy farms in south-west Victoria. FECs were measured in recently calved primiparous and multiparous cows. Individual FEC tests with a minimum detectable FEC of 2.5 eggs per gram of faeces (epg) and group larval cultures were completed. Farm management data and cow information was recorded for data analysis with the Jamovi statistical package. Overall, 35% of all cows had FEC ≥ 2.5 epg (26% of multiparous and 45% of primiparous). Ostertagi ostertagi was the predominant gastrointestinal nematode in all cohorts. Cooperia pectinata or C. punctata were also present in mixed infestations alongside C. oncophora. Multiparous cows in low body condition score post calving (<4) were more likely to have a FEC of >5 epg. Faecal egg counts at a minimum detectable FEC of 2.5 epg are effective indicators of parasitism in recently calved primiparous and poorly conditioned multiparous dairy cows. Increasing the test sensitivity (minimum detectable count) of FECs from 10 epg to 2.5 epg resulted in increasing the overall positive FEC rate from 15% to 35%. Further investigation of sensitive FECs and their relevance to production along with the timing and value of anthelmintic use in dairy cattle is warranted.