Evaluation of soil intake by growing Creole young bulls in common grazing systems in humid tropical conditions

Abstract

Soil is the main matrix which contributes to the transfer of environmental pollutants to animals and consequently into the food chain. In the French West Indies, chlordecone, a very persistent organochlorine pesticide, has been widely used on banana growing areas and this process has resulted in a long-term pollution of the corresponding soils. Domestic outside-reared herbivores are exposed to involuntary soil intake, and tethered grazing commonly used in West Indian systems can potentially favour their exposure to chlordecone. Thus, it appears necessary to quantify to what extent grazing conditions will influence soil intake. This experiment consisted of a cross-over design with two daily herbage allowance (DHA) grazed alternatively. Six young Creole bulls were distributed into two groups (G1 and G2) according to their BW. The animals were individually tethered and grazed on a restrictive (RES) or non-restrictive (NRES) levels of DHA during two successive 10-days periods. Each bull progressed on a new circular area every day. The two contrasting levels of DHA (P < 0.001) were obtained via a different daily grazing surface area (RES: 20 m 2 /animal, NRES: 31 m 2 /animal; P < 0.01) offered to the animals by the modulation of the length of the tethering chain (RES: 1.9 m, NRES: 2.6 m). These differences in offered grazing areas resulted in DHA of 71 and 128 g DM/kg BW 0.75 , respectively for RES and NRES treatments. As expected, the animals grazing on the reduced area realized a lower daily dry matter intake (DMI) (RES: 1.12 kg/100 kg BW, NRES: 1.83 kg/100 kg BW; P < 0.05) and present a lower organic matter digestibility (RES: 0.67, NRES: 0.73; P < 0.01) than NRES ones, due in part to the shorter post-grazing sward surface height (RES: 3.3 cm, NRES: 5.2 cm; P < 0.01) of their grazing circles. Soil intake was estimated on an individual level based on the ratio of the marker titanium in soil, herbage and faeces. Grazing closer to the ground, animals on RES treatment ingested a significantly higher proportion of soil in their total DMI (RES: 9.3%, NRES: 4.4%; P < 0.01). The amount of ingested soil in the diet was not significantly different between the two treatments (RES: 98 g/100 kg BW, NRES: 78 g/100 kg BW; P > 0.05) due to the lower DMI of RES compared with NRES treatment.

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

“…2). This postgrazing sward height near to 14 cm seemed to be relatively high compared to the range of 3.3-8.2 cm reported in previous works 5,6 but the important differences in postgrazing vegetation structure (long lying stems vs. short erected ones) limiting the comparison of postgrazing sward heights with these studies. Indeed, animals grazed on the experimental plot until resource depletion and at D12 the remaining vegetation cover was only constituted of lying fibrous stems forming an 'insulating carpet' above the ground (Fig.…”

“…3b and 3c). Previous studies conducted in tether-grazing growing bulls already reported a large range of variability in soil ingestions 5,6 ( Table 1). Given that in these experiments the animals presented similar age and BW, this interindividual variability can be attributed to differences in feeding behaviour between individuals.…”

“…While literature reported soil ingestion by cattle reaching 10% of the daily ingested DM 5,8 , the consequences on animal health, or on the diet digestibility, of such soil ingestions remain poorly documented to date. In chickens, high soil ingestion has been shown to decrease diet digestibility 12 .…”

Evidence for extensive anaerobic dechlorination and transformation of the pesticide chlordecone (C10Cl10O) by indigenous microbes in microcosms from Guadeloupe soil

“…Surface water, ground water, sediments and receiving coastal wasters have all been impacted. CLD has also been found to accumulate in animals [15][16][17] and plants used for food, including tubers and other vegetables grown in soil [18,19] as well as in marine fauna [9,20]. Effective methods to decontaminate soil and protect downgradient environments, food and water supply are clearly needed.…”

Relationship of mineral elements in sheep grazing in the highland agro-ecosystem

“…Among many important factors, soil minerals play an important role in sheep productivity and health status because sheep obtain their required nutrients from the feeds and fodder trees, which in turn derive in nutrients from the soil. During the grazing process, livestock intentionally or unintentionally ingest a small amount of soil, so a small amount of mineral elements from soil is directly consumed by the animals (Figure 1) [9]. The contribution of soil type and its nutritive composition of herbage can greatly contribute to the performance of live stock and are dependable in each environment [10].…”