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Abstract Copper (Cu) and zinc (Zn) are essential nutrients for swine. However, as pigs have a low retention rate for these elements, more than 90% of ingested Cu and Zn are excreted, mainly in feces. After spreading manure, these trace elements could accumulate in the soil and potentially have negative environmental effects. Moreover, Cu and Zn are also limited natural resources that should be preserved. A better understanding of the behavior of these elements throughout the feed-animal-effluent-treatment continuum according to feed composition and manure management chain is thus required to propose alternative ways to reduce these environmental impacts. Three feeding strategies differing in their Cu and Zn contents were compared in 72 growing-finishing pigs raised in individual pens from 24.3 ± 3.3 up to 110 ± 9.0 kg body weight (BW), one-half males; and one-half females a first diet with Cu and Zn at maximum EU regulation levels (20 and 100 ppm of Cu and Zn, respectively; REG), a second diet without any Cu and Zn supplementation (5 ppm Cu, 30 ppm Zn; WS) and a third diet with Cu and Zn at an intermediary level (10 and 50 ppm of Cu and Zn; INT). Cu and Zn were supplemented as Cu2O (CoRouge, Animine) and ZnO (HiZox, Animine), respectively. Eighteen additional finishing pigs (6 per diet) were raised in digestibility cages for excreta collection over 10 d, and their feces were submitted to two types of manure treatment: anaerobic digestion (AD) and composting with straw. Over the entire experimental period, the dietary Cu and Zn content did not influence growth performance of pigs. The Cu and Zn concentrations of the feces decreased linearly (P 0.001) with dietary content from 191 and 834 (REG) up to 63 and 359 (INT) and 40 and 213 (WS) mg Cu and Zn/kg dry matter (DM) respectively. After both manure treatments, the degradation of the organic matter resulted in a significant increase (twice as much) in Cu and Zn concentration per kg of DM. Feeding strategy appears to be the main lever to reduce the Cu and Zn content of effluents. However, in the context of the diversification of manure management strategies, it is also important to take into account the effect of the effluent collection and treatment chain (e.g., spreading of raw slurry, phase separation, anaerobic digestion, composting), which has also an impact on the behavior of Cu and Zn and consequently on the risk for the environment.
Gourlez et al. (Sun,) studied this question.