Effect of sainfoin (Onobrychis viciifolia) on cyathostomin eggs excretion, larval development, larval community structure and efficacy of ivermectin treatment in horses.

Alternative strategies to chemical anthelmintics are needed for the sustainable control of equine strongylids. Bioactive forages like sainfoin (Onobrychis viciifolia) could contribute to reducing drug use, with the first hints of in vitro activity against cyathostomin free-living stages observed in the past. We analysed the effect of a sainfoin-rich diet on cyathostomin population and the efficacy of oral ivermectin treatment. Two groups of 10 naturally infected horses were enrolled in a 78-day experimental trial. Following a 1-week adaptation period, they were either fed with dehydrated sainfoin pellets (70% of their diet dry matter) or with alfalfa pellets (control group) for 21-days. No difference was found between the average fecal egg counts (FECs) of the two groups, but a significantly lower increase in larval development rate was observed for the sainfoin group, at the end of the trial. Quantification of cyathostomin species abundances with an ITS-2-based metabarcoding approach revealed that the sainfoin diet did not affect the nemabiome structure compared to the control diet. Following oral ivermectin treatment of all horses on day 21, the drug concentration was lower in horses fed with sainfoin, and cyathostomin eggs reappeared earlier in that group. Our results demonstrated that short-term consumption of a sainfoin-rich diet does not decrease cyathostomin FEC but seems to slightly reduce larval development. Consumption of dehydrated sainfoin pellets also negatively affected ivermectin pharmacokinetics, underscoring the need to monitor horse feeding regimes when assessing ivermectin efficacy in the field.

Chicory (Cichorium intybus) reduces cyathostomin egg excretion and larval development in grazing horses.

Cyathostomins are the most prevalent parasitic nematodes of grazing horses. They are responsible for colic and diarrhea in their hosts. After several decades of exposure to synthetic anthelmintics, they have evolved to become resistant to most compounds. In addition, the drug-associated environmental side-effects question their use in the field. Alternative control strategies, like bioactive forages, are needed to face these challenges. Among these, chicory (Cichorium intybus, Puna II cultivar (cv.)) is known to convey anthelmintic compounds and may control cyathostomins in grazing horses. To challenge this hypothesis, we measured fecal egg counts and the rate of larval development in 20 naturally infected young saddle horses (2-year-old) grazing either (i) a pasture sown with chicory (n = 10) or (ii) a mesophile grassland (n = 10) at the same stocking rate (2.4 livestock unit (LU)/ha). The grazing period lasted 45 days to prevent horse reinfection. Horses in the chicory group mostly grazed chicory (89% of the bites), while those of the control group grazed mainly grasses (73%). Cyathostomins egg excretion decreased in both groups throughout the experiment. Accounting for this trajectory, the fecal egg count reduction (FECR) measured in individuals grazing chicory relative to control individuals increased from 72.9% at day 16 to 85.5% at the end of the study. In addition, larval development in feces from horses grazed on chicory was reduced by more than 60% from d31 compared to control individuals. Using a metabarcoding approach, we also evidenced a significant decrease in cyathostomin species abundance in horses grazing chicory. Chicory extract enriched in sesquiterpenes lactones was tested on two cyathostomins isolates. The estimated IC50 was high (1 and 3.4 mg/ml) and varied according to the pyrantel sensitivity status of the worm isolate. We conclude that the grazing of chicory (cv. Puna II) by horses is a promising strategy for reducing cyathostomin egg excretion and larval development that may contribute to lower the reliance on synthetic anthelmintics. The underpinning modes of action remain to be explored further.

Do sheep (Ovis aries) categorize plant species according to botanical family?

The ability of grazing herbivores to assign food types to categories by relying on certain relevant criteria could considerably reduce cognitive demand and increase their foraging efficiency when selecting among many different plant items. Grasses and legumes differ functionally in vegetation communities as well as in nutritive value. We aimed to determine whether sheep can generalize an aversion they learnt for a grass or a legume species to another species of the same functional type and consequently whether botanical family is a potential level of categorization. Over four successive weeks, 12 lambs were conditioned against either a freshly cut grass (tall fescue-Festuca arundinacea, N = 6) or legume species (sainfoin-Onobrychis viciifolia, N = 6) using a negative post-ingestive stimulus (lithium chloride) on day 1. Preference of all lambs between another grass (cocksfoot-Dactylis glomerata) and another legume (alfalfa-Medicago sativa) was assessed on day 3 by measuring their relative consumptions. Preference for alfalfa progressively became lower for lambs that were conditioned against sainfoin than against tall fescue, indicating that lambs generalized the aversion between species along some perceptual gradient and classed the considered grasses and legumes in distinct categories. Beyond this original result, the question now is to identify which specific plant characteristics or functional traits the animals rely on in order to form categories.

Generalization of conditioned food aversions in grazing sheep and its implications for food categorization.

When grazing on heterogeneous pastures, herbivores may rely on food item generalization and categorization processes for reducing information processing while selecting their diet. The objective of this study was to assess the generalization of an aversion by grazing sheep for items differing by one or two criteria from an item against which they were negatively conditioned. Four items cultivated in pots were offered to the animals, resulting from the combination of an intrinsic criterion, i.e. grass species (ryegrass and fescue) and a transitory criterion, i.e. sward height (tall and short). We assessed the generalization process by comparing binary choices between the initially preferred tall ryegrass and the three other items, before and after animals had been partially conditioned against tall ryegrass. This method proved useful in assessing the generalization of an aversion. Sheep did not generalize their aversion on the basis of sward height but rather on species: they increased their preference for tall fescue and decreased their instantaneous preference for short ryegrass after having been conditioned against tall ryegrass. The generalization of an aversion through different states of a same species could indicate the possibility of a species-based categorization by grazing herbivores.

Do grazing sheep use species-based categorization to select their diet?

Food item categorization should reduce the cost of information processing by herbivores when selecting their diet in complex environments. We assessed the ability of sheep to categorize food items by offering them ryegrass (Rg) and fescue (Fe) in pots cut tall (T) or short (S). Ewes' preferences were tested in three binary choices, RgS-FeT, RgS-FeS and FeT-FeS, before and after aversive conditioning against RgT. After conditioning, the ewes decreased their preference for RgS, but their choice between tall and short fescue was unchanged. Thus the ewes generalized their aversion to the species but not to the sward height. Comparing the choices between the two species offered at the same height showed choices were similar between RgS and FeS here and between RgT and FeT in Ginane and Dumont (2006). We conclude that sheep can use species-based, open-ended categorization when selecting their diet, while other plant characteristics, such as sward height, are not used to define a category, despite their importance in diet selection.

Selection for nutrients by red deer hinds feeding on a mixed forest edge.

We studied the nutritional behaviour of hinds foraging on a mixed-forest edge by direct observation of their choices at each season and by measuring nutrient concentration in the plants. We compared nutrient concentrations in the observed diets with those in the total available vegetation, and with those of 1,000 randomly simulated diets in which we included only those plants that were actually eaten by the animal. Whether the available or the consumed feeds were used as the basis for comparisons had important consequences due to the presence of conifers and ferns, which were high in soluble sugars but were never eaten by the animals (potentially due to their toxicity). The selected diets were lower in sugars than the total available vegetation in summer, but were actually higher in sugars than the random diets generated from consumed forage species only. Hind diets contained more soluble sugars but not more protein than simulated diets in all seasons. Contrary to our prediction, anti-nutritional compounds (ADL and tannins) were avoided only in winter. Compared to simulated diets, hinds consumed more tannins in spring and summer and more ADL in summer and autumn. We suggest that this was a consequence of selection for soluble sugars, because the preferred plant species, which had high soluble sugar concentrations, also contained a large proportion of the anti-nutritional compounds eaten. In winter, the grass-dominated diets contained more fibre (NDF) and less ADL than the simulated diets, indicating that hinds orient their feeding towards digestible fibres. The switch from a browser to a grazer diet was related to a change in the availability of the nutrients, mainly soluble sugars. In our study, grasses contained more soluble sugars and proteins than deciduous browse during winter. This calls into question the dichotomy usually assumed in the literature between grass and browse in terms of nutrient content.