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

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.

Cattle exposure to chlordecone through soil intake. The case-study of tropical grazing practices in the French West Indies

Ingested soil is a major vector of organic contaminants from environment to free-ranged animals, particularly for grazing herbivores. Therefore, a better understanding of processes driving soil intake may provide new insights to limit animal exposure to contaminants and ensure safety of animal products. To maintain the supply service of livestock farming activities in contaminated areas, it is necessary to design adapted farming practices aiming at controlling the risk for human health. This study was conducted in the French West Indies, where chlordecone, an organochlorine insecticide previously used to protect banana plantation against the black weevil and banned since 1993, has polluted nearly 20% of agricultural surfaces since the 1970s. A crossover study design was performed to estimate soil intake by twelve tethered Creole young bulls according to different grazing practices. The objectives were to characterize the influence of (i) daily herbage allowance (LOW, HIGH, ADLIB: 100, 150, 300 g DM/kg BW^0.75 respectively); (ii) and soil surface moisture (SSM) testing grazing on a water-saturated (HUM) vs dried (DRY) ground. The herbage offer was managed via the allocated surfaces varying the chain length as animal holders commonly do in informal Caribbean systems. The results evidenced an increase in soil intake with DHA reduction (2.1 to 3.8% of DM intake; P < 0.05) and with SSM increase (2.4 to 3.6% of DM intake; P < 0.05). Herbage offer reduction involved a closer-to-the-ground grazing with shorter post-grazing sward surface height (82.2 to 63.3 mm; P < 0.001), and both herbage offer reduction and SSM increase amplified sward soiling (measured from titanium content in unwashed herbage and image analysis). This work showed that soil intake is unavoidable even when herbage offer is very generous. The animals will significantly increase soil intake when herbage offer would be at 150 g DM/kg BW^0.75 or less, especially when the grazed surface is humid.

Consumo de forragem por ovinos ingerindo grama missioneira gigante com ou sem acesso a amendoim forrageiro

RESUMO A grama missioneira gigante (Axonopus catharinensis Valls) é uma espécie forrageira que merece ser melhor investigada tanto pura como recebendo a inclusão de leguminosas. Objetivou-se avaliar o consumo de MS por ovinos pastejando grama missioneira gigante com ou sem acesso a pastos de amendoim forrageiro (Arachis pintoi cv. Amarillo). Para isso, foi conduzido um experimento prévio com cordeiros alojados em gaiolas metabólicas, gerando-se uma equação para a estimativa do consumo tomando como base a excreção fecal de proteína bruta (PBf), que apresentou R2= 0,91. Em um segundo experimento, foi avaliado o consumo de forragem por ovinos em pastos de grama missioneira gigante com duas alturas de entrada (25 ou 35cm), com ou sem acesso a áreas de amendoim forrageiro por duas horas diárias. A altura de entrada na grama missioneira gigante não alterou o consumo total de MS, mas o acesso aos piquetes da leguminosa aumentou o consumo em aproximadamente 20%. Em conclusão, a grama missioneira gigante pode ser manejada com alturas de entrada entre 25 e 35cm, enquanto o acesso a áreas de amendoim forrageiro por duas horas diárias aumenta o consumo de MO por cordeiros pastejando a missioneira.

Estimating the digestibility of Sahelian roughages from faecal crude protein concentration of cattle and small ruminants

Studies on diet selection and feed intake of ruminants in extensive grazing systems often require the use of simple approaches to determine the organic matter digestibility (OMD) of the ingested feed. Therefore, we evaluated the validity of the one-factorial exponential regression established by Lukas et al. [Journal of Animal Science 83 (2005) 1332], which estimates OMD from the faecal crude protein (FCP) concentration. The equation was applied to two sets of data obtained with free grazing and pen-fed cattle, sheep and goats ingesting low and high amounts of green and dry vegetation of Sahelian pastures as well as millet leaves and cowpea hay. Data analysis showed that the livestock species did not influence the precision of estimation of OMD from FCP. For the linear regression between measured and estimated OMD (%) across n = 431 individual observations, a regression coefficient of r2 = 0.65 and a residual standard deviation (RSD) of 5.87 were obtained. The precision of estimation was influenced by the data set (p = 0.033), the type of feed (p < 0.001) and the feeding level (p = 0.009), and interactions occurred between type of feed and feeding level (p = 0.021). Adjusting the intercept and the slope of the established exponential function to the present data resulted in a compression of the curve; while r2 remained unchanged, the RSD of the regression between measured and estimated OMD was reduced, when compared with the results obtained from the equation of Lukas et al. (2005). Estimating OMD from treatment means of FCP greatly improved the correlation between measured and estimated OMD for both the established function and the newly fit equation. However, if anti-nutritional dietary factors increase the concentration of faecal nitrogen from feed or endogenous origin, the approach might considerably overestimate diet digestibility.

Relationship between fecal crude protein concentration and diet organic matter digestibility in cattle1

The positive relationship between fecal CP concentration and diet OM digestibility in cattle, which is based on increasing undigested microbial CP and decreasing fecal OM as OM digestibility increases, may be used as an indirect method for estimating diet OM digestibility from fecal CP concentration. Results of digestibility trials (445 individual observations) conducted at Hohenheim and Braunschweig, Germany, and at Gumpenstein, Austria, were used to study the relationship between CP concentration in feces (x, g/kg OM) and OM digestibility (y, %). The best fit was obtained with the curvilinear relationship y = ai -107.7e(-0.01515 x x), with a1 = 79.76 and a2 = 72.86 (R2 = 0.82; residual SD = 2.7; SE = 0.13), which takes into account the effects of location (i = 1 for Braunschweig and Hohenheim, and i = 2 for Gumpenstein). Dietary CP and crude fat concentration, and DMI had no effect on fecal CP content, whereas crude fiber content, proportion of concentrate in the diet, and forage type significantly affected CP concentration in feces; however, the magnitude of these effects was less than 2 percentage units, and the direction of the effect of proportion of concentrate in the diet was not uniform. The curvilinear relationship between fecal CP concentration (observed range, 100 to 300 g/kg of OM) and diet OM digestibility (observed range = 57 to 80%) may be used to estimate diet OM digestibility, particularly for field trials, as it requires no feed samples and does not physically restrict the animal.