The aim of this review is to focus the attention on the nutrition ecology of the heavy metals and on the major criticisms related to the heavy metals content in animal feeds, manure, soil and animal-origin products. Heavy metals are metallic elements that have a high density that have progressively accumulated in the food chain with negative effects for human health. Some metals are essential (Fe, I, Co, Zn, Cu, Mn, Mo, Se) to maintain various physiological functions and are usually added as nutritional additives in animal feed. Other metals (As, Cd, F, Pb, Hg) have no established biological functions and are considered as contaminants/undesirable substances. The European Union adopted several measures in order to control their presence in the environment, as a result of human activities such as: farming, industry or food processing and storage contamination. The control of the animal input could be an effective strategy to reduce human health risks related to the consumption of animal-origin products and the environmental pollution by manure. Different management of raw materials and feed, animal species as well as different legal limits can influence the spread of heavy metals. To set up effective strategies against heavy metals the complex interrelationships in rural processes, the widely variability of farming practices, the soil and climatic conditions must be considered. Innovative and sustainable approaches have discussed for the heavy metal nutrition ecology to control the environmental pollution from livestock-related activities.

An investigation was conducted to test the hypothesis that dietary oil inclusion increases ammonia nitrogen (NH3-N) emission from the manure, due to a negative effect of either unsaturated or saturated oil on microbial activity in the intestine. Dietary oil was included at 45 g/kg, as either crude palm oil (PO), soya oil (SO) or a 50: 50 SO: PO blend (OB), to a basal barley-soya-wheat diet (control) at the expense of dextrose and maize starch. Diets were formulated to contain 13·2 MJ digestible energy per kg and 11·0 g/kg lysine. Four boars were assigned to each dietary treatment, and were transferred to metabolism crates (mean live weight, 74·0 (± 2·89) kg) following 14 days dietary acclimatization. Urine and faeces were collected separately over a 5-day digestibility/nitrogen (N) balance period and a 2-day manure collection period. Inclusion of dietary oil increased apparent digestibility of oil (P < 0·01) and decreased the apparent digestibility of dry matter (P < 0·01) and gross energy (P < 0·05). Dietary oil did not affect the apparent digestibility of nitrogen, acid-detergent fibre, neutral-detergent fibre or hemicellulose. Apparent digestibility of oil was lower when oil was included as PO compared with SO and OB (P < 0·001). The concentration of faecal volatile fatty acid (VFA) was similar in all treatments, although the acetic: propionic acid ratio was lower when oil was included as PO and OB compared with SO (P < 0·05). N balance, manure N concentration and NH3-N emission was not affected by oil inclusion or oil source. In conclusion, dietary oil inclusion reduced apparent dry matter and energy digestibilities, although no effect on fermentation was indicated by digestibility of fibre or faecal VFA content. Consequently, ammonia emission was not affected by dietary oil included at 45 g/kg.