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.

Energy supplementation and herbage allowance effects on daily intake in lactating mares

Little is known about how to manage grazing horses, including the thresholds under which energy supplementation is required. Here we investigated the effects of daily herbage allowance (DHA) and energy supplementation (ES) on daily herbage intake in lactating mares of light breeds grazing high-quality regrowth during summer. Three contrasting DHA, low (LOW), medium (MED), and high (HIGH), that is, 35.0, 52.5, and 70.0 g DM∙kg BW(-1)∙d(-1), respectively, were obtained by adjusting pasture strip width. Eighteen Anglo-Arab and French Saddle lactating mares were either supplemented with 2.6 kg DM barley/d (SUP group; n= 9) or left nonsupplemented (NSUP group; n = 9) throughout the experiment. For 3 successive 2-wk periods, 3 groups of SUP mares (n = 3) and 3 groups of NSUP mares (n = 3) grazed each DHA according to a 3 × 3 Latin square design. Pregrazing sward surface height (SSH) was similar between treatments (26.6 cm), but postgrazing SSH differed significantly between each DHA (2.9, 4.4, and 5.7 cm for LOW, MED, and HIGH, respectively; P < 0.001). Herbage DMI (HDMI) increased linearly from 18.5 to 23.4 g DM∙kg BW(-1)∙d(-1) with increasing DHA (i.e., 0.13 kg DM eaten/kg DM of herbage offered; P < 0.001) independently of ES and with no significant ES × DHA interaction. This increase in HDMI resulted from an increase in grazing time between LOW (961 min/d) and MED and HIGH (1,021 min/d; P < 0.01) and from an increase in intake rate between LOW and MED (11.8 g DM/min) and HIGH (13.6 g DM/min; P < 0.01). Total digestible DMI (TDDMI) and NE intake (NEI) increased linearly from 12.3 to 15.2 g DM∙kg BW∙(-1)d(-1) and from 136.6 to 165.8 kJ∙kg BW(-1)∙d (-1)with increasing DHA (P < 0.001), respectively. Total digestible DMI and NEI were significantly lower for NSUP than for SUP mares: 12.5 vs. 14.9 g DM∙kg BW(-1)∙d(-1) (P < 0.01) and 134.6 vs. 166.5 kJ∙kg BW(-1)∙d(-1) (P < 0.001), respectively. Whereas SUP mares always met their energy requirements, NSUP mares no longer met theirs when DHA fell below 66 g DM∙kg BW(-1)∙d(-1) (i.e., 39 kg DM∙mare(-1)∙d(-1)).