UR Animal et Fonctionnalités des Produits Animaux, INRA Nancy Université, 2 av. de la forêt de Haye, BP 172, 54505 Vandoeuvre cedex, France.
Animal. 2012 Aug;6(8):1350-9. doi: 10.1017/S1751731111002734.
Involuntary soil intake by cows on pasture can be a potential route of entry for pollutants into the food chain. Therefore, it appears necessary to know and quantify factors affecting soil intake in order to ensure the food safety in outside rearing systems. Thus, soil intake was determined in two Latin square trials with 24 and 12 lactating dairy cows. In Trial 1, the effect of pasture allowance (20 v. 35 kg dry matter (DM) above ground level/cow daily) was studied for two sward types (pure perennial ryegrass v. mixed perennial ryegrass-white clover) in spring. In Trial 2, the effect of pasture allowance (40 v. 65 kg DM above ground level/cow daily) was studied at two supplementation levels (0 or 8 kg DM of a maize silage-based supplement) in autumn. Soil intake was determined by the method based on acid-insoluble ash used as an internal marker. The daily dry soil intake ranged, between treatments, from 0.17 to 0.83 kg per cow in Trial 1 and from 0.15 to 0.85 kg per cow in Trial 2, reaching up to 1.3 kg during some periods. In both trials, soil intake increased with decreasing pasture allowance, by 0.46 and 0.15 kg in Trials 1 and 2, respectively. In Trial 1, this pasture allowance effect was greater on mixed swards than on pure ryegrass swards (0.66 v. 0.26 kg reduction of daily soil intake between medium and low pasture allowance, respectively). In Trial 2, the pasture allowance effect was similar at both supplementation levels. In Trial 2, supplemented cows ate much less soil than unsupplemented cows (0.20 v. 0.75 kg/day, respectively). Differences in soil intake between trials and treatments can be related to grazing conditions, particularly pre-grazing and post-grazing sward height, determining at least in part the time spent grazing close to the ground. A post-grazing sward height lower than 50 mm can be considered as a critical threshold. Finally, a dietary supplement and a low grazing pressure, that is, high pasture allowance increasing post-grazing sward height, would efficiently limit the risk for high level of soil intake, especially when grazing conditions are difficult. Pre-grazing and post-grazing sward heights, as well as faecal crude ash concentration appear to be simple and practical tools for evaluating the risk for critical soil intake in grazing dairy cows.
在牧场上，奶牛非自愿地摄入土壤可能是污染物进入食物链的一个潜在途径。因此，了解和量化影响土壤摄入的因素似乎是必要的，以确保场外饲养系统的食品安全。因此，在两个拉丁方试验中用 24 头和 12 头泌乳奶牛确定了土壤摄入。在第 1 个试验中，研究了在春季两种草地类型（纯多年生黑麦草 v. 多年生黑麦草-白三叶草混合）下，草地允许量（20 或 35 公斤干物质（DM）高于地面水平/奶牛每天）的影响。在第 2 个试验中，研究了在秋季两个补充水平（0 或 8 公斤 DM 基于玉米青贮的补充）下，草地允许量（40 或 65 公斤 DM 高于地面水平/奶牛每天）的影响。土壤摄入是通过使用酸不溶性灰分作为内部标记的方法来确定的。在处理之间，第 1 个试验中每头奶牛的日干土摄入量范围为 0.17 至 0.83 公斤，第 2 个试验中为 0.15 至 0.85 公斤，在某些时期高达 1.3 公斤。在这两个试验中，土壤摄入量随着草地允许量的减少而增加，分别为第 1 个和第 2 个试验中的 0.46 和 0.15 公斤。在第 1 个试验中，这种草地允许量的影响在混合草地比在纯黑麦草地更大（中等和低草地允许量之间，每日土壤摄入减少 0.66 和 0.26 公斤，分别）。在第 2 个试验中，补充水平的草地允许量效应相似。在第 2 个试验中，补充喂养的奶牛比未补充喂养的奶牛吃的土壤少（分别为 0.20 和 0.75 公斤/天）。试验和处理之间的土壤摄入差异可以与放牧条件有关，特别是放牧前和放牧后的草地高度，这至少部分决定了在靠近地面放牧的时间。放牧后的草地高度低于 50 毫米可以被认为是一个临界阈值。最后，膳食补充剂和低放牧压力，即高草地允许量增加放牧后的草地高度，将有效地限制高水平土壤摄入的风险，特别是在放牧条件困难时。放牧前和放牧后的草地高度以及粪便粗灰浓度似乎是评估放牧奶牛临界土壤摄入风险的简单实用工具。
