A combined effort to avoid strongyle infection in horses in an oceanic climate region: rotational grazing and parasiticidal fungi

Abstract

Background: An approach to preventing strongyle infection in horses was tested, comprising rotational pasturing and the administration of spores of two parasiticidal fungi, Mucor circinelloides and Duddingtonia flagrans.

Methods: Twenty-two adult Spanish Sport Horses were dewormed with ivermectin (1 mg pour-on/kg body weight) and then randomly divided into three groups. G-1 was maintained with continuous grazing, and G-2 and G-3 were kept on a four-paddock rotation system. Commercial pelleted feed (2.5 kg/horse) was supplied to G-1 and G-2 twice a week; horses in G-3 received pellets containing 2 × 10⁶ spores/kg of each fungus. Fecal samples were analyzed by the flotation method to estimate the reduction in the fecal egg counts (FECR), the percentage of horses shedding eggs (PHR), and the egg reappearance period (ERP).

Results: Third-stage larvae were identified in fecal pats as Cyathostomum (sensu lato) types A, C and D, Gyalocephalus capitatus, Triodontophorus serratus, Poteriosthomum spp., Strongylus vulgaris and S. edentatus. Two weeks after treatment, the FECR values were 100% in G-1, 96% in G-2 and 99% in G-3; the PHR values were 100% in G-1, 75% in G-2 and 88% in G-3. A strongyle ERP of 6 weeks was observed in G-1, ERP of 10 weeks was observed in G-2, and ERP of 16 weeks was observed in G-3. The counts of eggs per gram of feces (EPG) were > 300 EPG in G-1 and G-2 but remained below 250 EPG in G-3 throughout the observation period of 12 months.

Conclusions: These results suggest that horse strongyle infection could be decreased by combining rotational pasturing with feeding pellets containing the spores of parasiticidal fungi.

Keywords: Duddingtonia flagrans; Horses; Integrated control; Mucor circinelloides; Pelleted feed; Rotational pasturing; Strongyles.

Fig. 1

Variations of climatic parameters in an oceanic climate area (NW Spain). Key: ♦, maximum temperature (°C); ▁, average temperature (°C); ▲, minimum temperature (°C); ✕, relative humidity (%); ■, number of frost days; ○, rainfall (l/m²); ┼, water balance (l/m²)

Fig. 2

Spores of Mucor circinelloides (a) and Duddingtonia flagrans (b) in feces of Spanish Sport Horses under a four-paddock rotation system, two days after provided pellets containing 2 × 10⁶ spores/kg of each fungus

Fig. 3

Kinetics of strongyle egg-output in Spanish Sport Horses under different pasturing regimes in an oceanic climate area (NW Spain). Key: (▬ ▬) G-1: continuous grazing and given pellets without fungal spores; (▬) G-2: four-paddock rotation system and pellets without fungal spores; (▪▪▪▪▪▪) G-3: four-paddock rotation system and pellets containing 2 × 10⁶ spores of Mucor circinelloides + 2 × 10⁶ spores Duddingtonia flagrans/kg. Points mean the average value, and error bars mean 2SD. Superscripts indicate time points differences between the strongyle egg-output values from G-1 and G-2 (1), G-2 and G-3 (2) and G-1 and G-3 (3)