Conflicto y Violencia

1.5.1.1 In vivo anthelmintic effects of forage chicory

Since the mid-1990’s, several in vivo studies have explored the potential anthelmintic effects of dietary forage chicory on parasitic nematodes, mainly in sheep (Scales et al., 1995; Marley et al., 2003b; Athanasiadou et al. 2005; Tzamaloukas et al., 2005; Tzamaloukas et al., 2006; Athanasiadou et al., 2007; Heckendorn et al., 2007; Nielsen et al., 2009; Kidane et al., 2010; Miller et al., 2011) but also in deer (Hoskin et al., 1999a) and cattle (Marley et al., 2014). The main parasitological findings of these in vivo studies, as well as the chicory cultivar used and the percentage of chicory DM in the diets, are summarised in Table 1.1. None of these studies investigated the content of SL in forage chicory, and when CT were screened they were detected at levels <0.5% CT in DM. Scales et al. (1995) reported a reduced FEC and Teladorsagia worm burden in lambs grazing forage chicory. They also recovered a lower number of infective L3 from chicory swards, as compared with ryegrass pastures. These authors described three hypothetic explanations for the reduced parasitism observed in lambs grazing chicory: i) a direct dietary modulation of chicory on the worms,

ii) an increased animal resilience to the infection (due to a higher nutritional quality) and/or iii) to an indirect reduction in pasture-borne infections (Scales et al., 1995). From the subsequent in vivo studies with chicory, particularly short feeding trials with experimental infections in lambs and preventing reinfection from pasture, it was strongly suggested that feeding forage chicory could directly affect abomasal worms, but not intestinal nematodes (Athanasiadou et al. 2005; Tzamaloukas et al., 2005; Heckendorn et al., 2007). Tzamaloukas et al. (2006) reported that lambs, trickle infected with T. circumcincta

circumcincta, evidenced by higher levels of mucosal mast cells and globule leucocytes in chicory lambs, and they attributed these findings to the high protein content in the chicory pasture, and not to a direct anthelmintic effect.

Marley et al. (2014) reported the only in vivo study to date exploring the anthelmintic effects of forage chicory in grazing cattle. In their study, beef steers were naturally infected with GI nematodes and grazed a mixed chicory/ryegrass pasture (~24% chicory DM in the field) for 18 weeks which resulted in similar FEC, proportion of O. ostertagi or Cooperia spp. L3 in larval cultures, serum pepsinogen and O. ostertagi-

antibodies levels compared to infected controls grazing ryegrass. Post-mortem worm counts were not conducted. Evidence from in vivo studies in sheep suggests that increased levels of chicory (≥50% chicory DM in the diet) may be necessary to affect GI parasitism in the host.

Table 1.1. Summary of published in vivo studies investigating the anthelmintic effects of forage chicory in ruminants. Species Chicory cv. Sown Chicory DM in diet (%)

Study design Effects in chicory fed animals Reference

Sheep Grasslands Puna

pure >85% Grazing, exp. + nat. infections with mixed GI nematodes

Lower FEC and Teladorsagia worm counts (P<0.05)

Scales et al., 1995

Deer Grasslands Puna

pure >56% Grazing, nat. infections with mixed GI nematodes and lungworms

No effect on FEC or lungworm L1 counts. Lower clinical signs associated with parasitism, requiring less anthelmintic treatment

Hoskin et al., 1999a

Sheep Grasslands Puna

pure n.i. Grazing, nat. infections with mixed GI nematodes

No effect on FEC or intestinal worm counts. 19-41% lower abomasal adult counts (P<0.001) and 32-60% lower abomasal L4 (P<0.01)

Marley et al., 2003b

Sheep n.i. pure 80% Grazing, exp. infections with

Trichostrongylus colubriformis

No effect on FEC, adult or immature worm counts

Athanasiadou et al., 2005

Sheep n.i. pure 87% Grazing, exp. infections with

Teladorsagia circumcincta

No effect on FEC, female per capita fecundity or immature worm counts. Reduction in adult male worms (P<0.01) and lower total adult counts by 43% (P=0.14)

Tzamaloukas et al., 2005

Sheep n.i. pure 91% Lambs trickle infected with T. circumcincta while grazing chicory. After anthelmintic treatment, lambs

No effect on FEC. Reduced numbers of late L4 and adult worms (P<0.05)

(continuation Table 1.1)

Sheep Grasslands Puna

pure ~80% Stabled lambs fed fresh-cut chicory. Exp. infections with Haemonchus contortus and Cooperia curticei

Reduced total egg output and FECDM of H. contortus (P<0.01). No effect on FECDM of C. curticei, on total FECDM or on adult worm counts

Heckendorn et al., 2007

Sheep Grasslands Puna

pure ~80% Grazing, nat. infections with mixed GI nematodes in ewes and lambs. Ewes were treated or not with anthelmintics

Lower FEC in lambs from untreated ewes on chicory (P<0.001). No effect on FEC of undrenched ewes or on adult worm burden in lambs

Athanasiadou et al., 2007 Sheep Grasslands Puna mixed 2-51% in the field; <6% intake

Grazing, nat. infections with mixed GI nematodes

No effect on FEC Nielsen et al., 2009

Sheep Puna II pure 50% Grazing, nat. infections with T. circumcincta

Reduced FEC (P<0.001) and lower L3 recovered from chicory swards (P=0.07)

Kidane et al., 2010

Sheep Oasis pure n.i. Grazing, nat. infections with mixed GI nematodes

Reduced FEC counts (P<0.05), lower FAMACHA scores requiring less anthelmintic treatments

Miller et al., 2011

Cattle Puna II mixed ~24% Grazing, nat. infections with GI nematodes

No effect on FEC, proportion of O. ostertagi or Cooperia spp. L3 in larval cultures, serum pepsinogen or O. ostertagi-antibodies

Marley et al., 2014

1.5.1.2 Effect of forage chicory on the development and survival of free-living nematode stages

Studies have also described a lower recovery of infective L3 in chicory pastures, potentially attributed to a reduced development of free-living stages. Moss and Vlassoff (1993) reported a lower recovery of total L3 from a pure chicory sward, compared with a ryegrass field, seeded with strongyle and Nematodirus spp. eggs. The authors attributed their findings to the markedly lower DM in the chicory field (40% less DM, compared with ryegrass) which could have changed the micro-climate in the sward and limited the development and survival of L3 (Moss and Vlassoff, 1993). Reduced herbage mass and plant cover has also been suggested to limit the development and survival of larval stages from sheep nematode (Thamsborg et al., 1996). Niezen et al. (1998) described a lower total number of L3 and reduced larval survival, particularly of T. circumcincta, recovered from a chicory sward seeded with GI nematode eggs, as compared with a ryegrass field. No information of the DM in the chicory field was provided. Marley et al. (2006) reported a significantly lower recovery of L3 (per kg forage DM) from chicory seeded with C. curticei eggs and cultivated under greenhouse conditions (as compared with ryegrass) and a significantly lower T. circumcincta L3 (per kg forage DM) from chicory swards (compared to ryegrass pastures). Kidane et al. (2010) recovered a lower number of L3 from a chicory sward grazed by naturally infected lambs, although not significantly different from the larval recovery from a ryegrass/clover field. These studies strongly suggest a potentially lower infection pressure on animals grazing chicory swards. Experiments have also explored a potentially reduced development of free-living nematode stages isolated from animals fed with forage chicory. Schreurs et al. (2002) reported no differences in the in vitro

egg hatching or larval development of GI nematodes isolated from faeces of deer grazing chicory. In contrast, Marley et al. (2003a) observed a significantly lower development of H. contortus and C. curticei eggs into L3 in cultured faeces from lambs fed with forage chicory, in comparison with the larval development in faeces from animals grazing ryegrass/clover. A decreased larval development of T. colubriformis has also been reported in faeces from animals fed CT-rich diets (Niezen et al., 2002).

The available literature summarised here suggests that forage chicory can negatively affect infections with GI nematodes through: a) direct anthelmintic effects on parasites in the host, b) indirect effects through improved nutrition and enhancement of immunity, and c) a reduced larval intake from pasture due to a lower development and survival of infective nematode stages in chicory swards and in faeces of chicory-fed animals. The direct anthelmintic effects of chicory, which are the main subject of this PhD thesis, are believed to derive from its content of bioactive compounds or plant secondary metabolites (PSM).