Advances in nutrient metabolism and emission of livestock and poultry dietary trace elements

Abstract

Trace elements, including iron, copper, manganese, zinc, selenium, and iodine, comprise less than 0.01% of animals, yet are essential nutrients and key factors in the plant-animal-soil cycle. Trace elements have important physiological functions and are often required for enzymatic reactions, energy metabolism, and synthesis of materials, immune defense, and other activities necessary for life. Micronutrient deficiency causes developmental disorders and decreased immunity in young animals, and even leads to nutritional metabolic diseases and death. Supplementation of the diet of livestock and poultry with trace elements is closely related to growth and reproductive performance. Many studies have demonstrated that dietary supplementation with trace elements improves production performance and the content of these elements in livestock and poultry products. Due to the low bioavailability of dietary trace elements, excess trace elements may be added to livestock and poultry diets. However, animals generally have self-regulatory mechanisms of absorption and metabolism to maintain the homeostasis of trace elements. Excess dietary trace elements that are not absorbed are discharged in the excrement and pollute farm soil and water sources. In particular, heavy metals, such as copper, zinc, manganese, chromium, and cadmium, detrimentally affect the growth of crops and change the composition and structure of soil microorganism. Human health can also be affected when heavy metals bioaccumulate through the food chain. Breeding and consumption of livestock and poultry occur on a large scale in China, the excrement from livestock and poultry is an important source of heavy metals in the environment. Soil, water, and crops in most areas of China are seriously affected by heavy metal pollution. Clarifying the nutrient metabolism and emission of dietary trace elements to reduce environmental con-tamination is crucial to improve the economic benefits of breeding, protect the ecological environment of breeding areas, and promote the healthy and sustainable development of the breeding industry. In recent years, increasing attention has focused on reducing environmental pollution caused by heavy metals from livestock and poultry, while maintaining the efficiency of breeding production. Appropriate reductions of trace elements in livestock and poultry diets do not impact growth performance and reduce the content of trace elements in excreta. In addition, organic trace element additives demonstrate higher bioavailability with less emission. This article summarizes the nutritional function, absorption and metabolism mechanism, enrichment characteristics of livestock and poultry products, and fecal excretion patterns of trace elements. The appropriate lower levels, improved dosage form of supplemented dietary trace elements, and a model of combined planting and breeding may alleviate trace element pollution in livestock and poultry breeding.