Prevalence and seasonal dynamic of gastrointestinal parasites in equids in France during two years.

Grazing equids are constantly exposed to three clinically important gastrointestinal parasites (small strongyles/cyathostomins, Anoplocephala spp. and Parascaris spp.). Knowledge of the local seasonal dynamic of these parasitic infections is important for constructing a sustainable parasite control program with a rational number of anthelmintic treatments. However, studies describing these patterns are sparse in France. In this context, a two-year study was carried out to assess i) the seasonal dynamic and variability of strongyle faecal egg counts (FEC) and infective larvae (L3) counts on pastures, and ii) the prevalence of Anoplocephala spp. and Parascaris spp. and the dynamic evolution of their presence. During 2021 and 2022 grazing seasons, monthly individual faecal egg counts (FEC) and diarrhea scores (DS) were determined on 428 equids divided into 33 groups. A monthly body condition score (BCS) was also attributed to animals ≥3 years old and a monthly bodyweight was estimated for each animal <3 years old. At the group level, the strongyle L3 counts on grazed pastures were carried out at least in spring, summer and autumn. Eggs of strongyles were observed in 97% of equids. In 64% of the groups, the peaks of FEC were noted in September and October. At the individual level, the maximum strongyle FEC was related to age, group of breeds, number of grazed plots and number of anthelmintic treatments. No negative association was observed between strongyle FEC and BCS or average daily weight gain. In the pastures, cyathostomin larvae were found almost exclusively. Over the two years, the peaks of cyathostomin L3 counts occurred in 87% of the groups between September and November and ranged from 635 to 87,500 L3 kg-1 dry herbage. The variability of the maximum cyathostomin L3 count in each group was explained by the year and the number of grazed plots. Eggs of Anoplocephala spp. were observed in 12% of equids. Eggs of Parascaris spp. were noted in 34% of one year-old animals, 9% of two years-olds and 2% of olders. Anoplocephala spp. and Parascaris spp. eggs were observed every month with a peak in the percentage of shedders in groups in October for Anoplocephala spp. and May-June for Parascaris spp.This study highlights the prevalence of each parasite, the variability in cyathostomin egg excretion and L3 counts amongst groups and individuals and the factors involved in this variation These local epidemiological data will help us to re-think a newer strategy against these parasites.

To treat or not to treat: diagnostic thresholds in subclinical helminth infections of cattle.

Helminth infections of cattle place significant burdens on livestock production and farm economic efficiency. Heavy infections are relatively easy to detect and treat with anthelmintics. However, subclinical infections have major but often hidden impacts on animals, necessitating more refined diagnostics to detect them and ideally inform farmers about the likely impact of anthelmintic treatment on animal and herd performance. Here, we review recent advances in diagnosing three major cattle helminth infections - gastrointestinal nematodes (GINs), liver flukes, and lungworms - and the search for subclinical infection thresholds to guide treatment decisions. Combining refined diagnostic thresholds with farm-specific information on grazing systems and animal history enables farmers to tailor helminth treatments to specific epidemiological circumstances, thereby limiting anthelmintic resistance (AR) and boosting agricultural efficiency and food security.

Rapid assessment of faecal egg count and faecal egg count reduction through composite sampling in cattle.

BACKGROUND: Faecal egg counts (FEC) and the FEC reduction test (FECRT) for assessing gastrointestinal nematode (GIN) infection and efficacy of anthelmintics are rarely carried out on ruminant farms because of the cost of individual analyses. The use of pooled faecal samples is a promising method to reduce time and costs, but few studies are available for cattle, especially on the evaluation of different pool sizes and FECRT application. METHODS: A study was conducted to assess FEC strategies based on pooled faecal samples using different pool sizes and to evaluate the pen-side use of a portable FEC-kit for the assessment of FEC on cattle farms. A total of 19 farms representing 29 groups of cattle were investigated in Italy and France. On each farm, individual faecal samples from heifers were collected before (D0) and two weeks after (D14) anthelmintic treatment with ivermectin or benzimidazoles. FEC were determined individually and as pooled samples using the Mini-FLOTAC technique. Four different pool sizes were used: 5 individual samples, 10 individual samples, global and global on-farm. Correlations and agreements between individual and pooled results were estimated with Spearman's correlation coefficient and Lin's concordance correlation coefficients, respectively. RESULTS: High correlation and agreement coefficients were found between the mean of individual FEC and the mean of FEC of the different pool sizes when considering all FEC obtained at D0 and D14. However, these parameters were lower for FECR calculation due to a poorer estimate of FEC at D14 from the faecal pools. When using FEC from pooled samples only at D0, higher correlation and agreement coefficients were found between FECR data, the better results being obtained with pools of 5 samples. Interestingly, FEC obtained on pooled samples by the portable FEC-kit on-farm showed high correlation and agreement with FEC obtained on individual samples in the laboratory. This field approach has to be validated on a larger scale to assess its feasibility and reliability. CONCLUSIONS: The present study highlights that the pooling strategy and the use of portable FEC-kits on-farm are rapid and cost-effective procedures for the assessment of GIN egg excretion and can be used cautiously for FECR calculation following the administration of anthelmintics in cattle.

Design and evaluation of multi-indicator profiles for targeted-selective treatment against gastrointestinal nematodes at housing in adult dairy cows.

Targeted-selective treatments against gastrointestinal nematode (GIN) in adult dairy cows require the identification of "cows to treat", i.e. cows whose milk production (MP) would increase after treatment. This study aimed at quantifying the ability of multi-indicator profiles to identify such cows. A randomized controlled clinical trial was conducted at housing in 25 French pasturing dairy herds. In each herd, treated cows received fenbendazole orally, control cows remained untreated. Daily MP was recorded and the MP variation between the pre- and post-visit periods was calculated (ΔMP) for each cow. ΔMP was modelled with control cows data (n=412) (piecewise linear mixed model). Estimated parameters were applied to treated cows data (n=414) to predict the expected ΔMP in treated cows if they had not been treated. Treated cows with an observed ΔMP (with treatment) higher than the expected ΔMP (without treatment) were labelled as "cows to treat". Herds where at least 50% of the young cows were "cows to treat" were qualified as "herds to target". To characterize such cows and herds, the available candidate indicators were (i) at the cow-level: parity, stage of lactation and production level, faecal egg count (FEC), serum pepsinogen level and anti-Ostertagia antibody level (expressed as ODR); (ii) at the herd-level: bulk tank milk (BTM) Ostertagia ODR, Time of Effective Contact (TEC, in months) with GIN infective larvae before the first calving, and percentage of positive FEC. These indicators were tested one-by-one or in combination to assess their ability to characterize "herds to target" and "cows to treat" (Chi-square tests). 115 out of 414 treated cows (27.8%) were considered as "cows to treat", and 9 out of 22 herds were qualified as "herds to target". The indicators retained to profile such cows and herds were the parity, the production level, the BTM Ostertagia ODR and the TEC. Multi-indicator profiles were much more specific than single indicator profiles, induced lower treatment rates, thereby minimizing the selection pressure on parasite populations. Particularly, to target a herd, the specificity was better with the profile "high BTM Ostertagia ODR and low-TEC" than with the BTM ODR value taken into account alone. The targeted-selective treatment of "young cows, belonging to herds with a high BTM ODR at housing and a low TEC" appeared as a pertinent solution, enabling a global approach for the control of GIN infection in which GIN control in heifers is connected to GIN control in adult cows.

Impact of Low and High Doses of Marbofloxacin on the Selection of Resistant Enterobacteriaceae in the Commensal Gut Flora of Young Cattle: Discussion of Data from 2 Study Populations.

In the context of requested decrease of antimicrobial use in veterinary medicine, our objective was to assess the impact of two doses of marbofloxacin administered on young bulls (YBs) and veal calves (VCs) treated for bovine respiratory disease, on the total population of Enterobacteriaceae in gut flora and on the emergence of resistant Enterobacteriaceae. In two independent experiments, 48 YBs from 6 commercial farms and 33 VCs previously colostrum deprived and exposed to cefquinome were randomly assigned to one of the three groups LOW, HIGH, and Control. In LOW and HIGH groups, animals received a single injection of, respectively, 2 and 10 mg/kg marbofloxacin. Feces were sampled before treatment, and at several times after treatment. Total and resistant Enterobacteriaceae enumerating were performed by plating dilutions of fecal samples on MacConkey agar plates that were supplemented or not with quinolone. In YBs, marbofloxacin treatment was associated with a transient decrease in total Enterobacteriaceae count between day (D)1 and D3 after treatment. Total Enterobacteriaceae count returned to baseline between D5 and D7 in all groups. None of the 48 YBs harbored marbofloxacin-resistant Enterobacteriaceae before treatment. After treatment, 1 out of 20 YBs from the Control group and 1 out of 14 YBs from the HIGH group exhibited marbofloxacin-resistant Enterobacteriaceae. In VCs, the rate of fluoroquinolone-resistant Enterobacteriaceae significantly increased after low and high doses of marbofloxacin treatment. However, the effect was similar for the two doses, which was probably related to the high level of resistant Enterobacteriaceae exhibited before treatment. Our results suggest that a single treatment with 2 or 10 mg/kg marbofloxacin exerts a moderate selective pressure on commensal Enterobacteriaceae in YBs and in VCs. A fivefold decrease of marbofloxacin regimen did not affect the selection of resistances among commensal bacteria.

Unexpected Decrease in Milk Production after Fenbendazole Treatment of Dairy Cows during Early Grazing Season.

Gastrointestinal nematodes (GIN) infection can impair milk production (MP) in dairy cows. To investigate whether MP would be optimized by spring targeted-selective anthelmintic treatment in grazing cows, we assessed (1) the effect on MP of an anthelmintic treatment applied 1.5 to 2 months after turn-out, and (2) herd and individual indicators associated with the post-treatment MP response. A randomized controlled clinical trial was conducted in 13 dairy farms (578 cows) in western France in spring 2012. In each herd, lactating cows of the treatment group received fenbendazole orally, control cows remained untreated. Daily cow MP was recorded from 2 weeks before until 15 weeks after treatment. Individual serum pepsinogen and anti-Ostertagia antibody levels (expressed as ODR), faecal egg count and bulk tank milk (BTM) Ostertagia ODR were measured at treatment time. Anthelmintic treatment applied during the previous housing period was recorded for each cow. In each herd, information regarding heifers' grazing and anthelmintic treatment history was collected to assess the Time of Effective Contact (TEC, in months) with GIN infective larvae before the first calving. The effect of treatment on weekly MP averages and its relationships with herd and individual indicators were studied using linear mixed models with two nested random effects (cow within herd). Unexpectedly, spring treatment had a significant detrimental effect on MP (-0.92 kg/cow/day on average). This negative MP response was particularly marked in high producing cows, in cows not treated during the previous housing period or with high pepsinogen levels, and in cows from herds with a high TEC or a high BTM ODR. This post-treatment decrease in MP may be associated with immuno-inflammatory mechanisms. Until further studies can assess whether this unexpected result can be generalized, non-persistent treatment of immunized adult dairy cows against GIN should not be recommended in early grazing season.