Dispersal and concentration of sheep gastrointestinal nematode larvae on tropical pastures
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© 2019 Elsevier B.V. Knowledge of free-living stages of endoparasite population ecology may guide their control in domesticated ruminants. Our objective was to evaluate sheep gastro-intestinal nematode (GIN) L3 distribution in tropical pasture profiles (grass and legume). Three different swards (treatments) were compared: 1) grass-only (G), 2) legume-only (L), and 3) one half of the paddock with grass and another half with legume (GL). We assessed pasture larval counts (PLC) in upper, medium and bottom strata, each representing one third of the sward height. Lamb health and performance characteristics were also evaluated. The PLC per kg of herbage dry matter (DM) tended to be 129% greater (P = 0.08) in the upper pasture profile compared to the lower stratum in GL pasture. However, the largest PLC dispersed per area (PLC/m²) was found (P < 0.01) in the lowest stratum in all pasture types. The overall PLC, averaged over strata, tended to be greatest (P = 0.09) in GL pasture (377 ± 45 L3/kg DM) when compared to G or L pastures (178 ± 13 L3/kg DM and 160 ± 16 L3/kg DM, respectively). The PLC dispersion in the area (L3/m²) was not different among pasture types (47.0 ± 4.1 L3/m²; P = 0.63). The PLC dispersion by area was negatively correlated with lamb average daily gain (ADG; r = -0.68, P < 0.01) and positively correlated with precipitation (r = 0.78; P < 0.01). No differences among treatments were detected for lamb performance (P = 0.19). All treatments showed high infection rates but L tended to have greater fecal egg counts (FEC; P = 0.062). The GL swards also tended to have 112 and 136% greater (P = 0.09) PLC per kilogram of DM compared to G and L, respectively. The dispersal of larvae by area showed to be an important measure to describe the pasture L3 contamination, it is highly correlated with lamb average daily gain.
author list (cited authors)
Tontini, J. F., Poli, C., da Silva Hampel, V., Fajardo, N. M., Martins, A. A., Minho, A. P., & Muir, J. P.