Dynamics of soil ingestion by growing bulls during grazing on a high sward height in the French West Indies

Claire Collas,Pierre-Marie Badot,Nadia Crini,Maurice Mahieu,Cyril Feidt,Stefan Jurjanz,Guido Rychen

doi:10.1038/s41598-020-74317-0

Abstract

Free-range livestock are exposed to environmental contaminants by ingesting contaminated matrices mainly soil. Several works evaluated precisely the soil ingestion and its variation factors in ruminants. Contrary to temperate grazing systems, tropical ones were poorly documented whereas weather or traditional grazing practices may change models established in temperate systems. The study was performed in the French West Indies, which are concerned by a widespread environmental chlordecone contamination. The work evaluated daily soil and grass ingestions by tethered growing bulls grazing on a very high sward close to 50 cm for 11 days without being moved. This grazing management is representative to local practices by small farmers or not professional holders and allows completing the results previously obtained. Daily soil ingestion did not significantly increase across time and was on average 26.9 g dry matter/100 kg body weight (i.e. 1.4% of the total mass ingested). Marked individual variations indicated that exposure risk assessments would require experimental designs based on a sufficient number of individuals. This study was also the first to investigate the changes in sward soiling with respect to the distance from the stake and reported lower soil loading on grass in the peripheral than central and intermediate areas.

Highlights

Soil ingestion represents a major risk of exposure to environmental pollutants for free range animals without any supply of bioavailable n utrients[1,2]
These results suggest that restricted animals would graze closer to the ground and could be subjected to a higher soil ingestion, so sward height can be a grazing management tool to limit soil ingestion
The present study completed the approach of soil ingestion in tethered growing cattle with estimation of soil ingestion when tethered cattle stay during 11 days on the same plot with a large surface (‘long chain’) and a very high sward as it is frequently met in grazing practices among Caribbean breeders

Summary

Introduction

Soil ingestion represents a major risk of exposure to environmental pollutants for free range animals without any supply of bioavailable n utrients[1,2]. For similar pregrazing sward heights, it was observed that the postgrazing sward height was lower for animals receiving a restricted herbage allowance than for animals receiving a higher herbage allowance (3.3 vs 5.2 cm5; 6.3 vs 8.2 cm[6]) These results suggest that restricted animals would graze closer to the ground and could be subjected to a higher soil ingestion, so sward height can be a grazing management tool to limit soil ingestion. Tethered-grazing is a common practice in Caribbean especially for not professional private holders[7] It can be conducted differently when available biomass is very high, with tall forage species often reaching a height over 0.5 m above the ground, as in ancient banana plantations potentially polluted by chlordecone. This study targeted to understand better the influence of grazing on spatial and temporal variations of soil loading on grass

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Conclusion