Effects of low protein feeding technology on maturity of the pig manure composting

Objectives It is difficult to store and treat pig manure due to its large production, low C/N and high water content. The aerobic stacking of pig manure results in low stacking efficiency due to the poor microbial activity environment provided by raw materials. The low protein feeding technology can reduce the nitrogen input in the feed without affecting the growth and development of pigs, and can change the nutrient composition of pig manure. This study analyzed whether pig manure produced by low protein diet feed could quickly and effectively reach maturity through different stacking methods and judging various organic manure maturity indexes, which met the safety application standards.

Methods In animal experiments, 72 castrated boars with an initial weight of 50 kg were selected and divided into high and low protein feeding groups with 6 replicates for each group and 6 pigs for each replicate. The experimental pigs took 7 days to get used to the diets before the dung collection was started, and the whole collection period was 60 days long. The dung produced by both the high and low protein feeding groups were composted under static and aerobic conditions, the four treatments were namely high protein feeding static stacking (MH), low protein feeding static stacking (ML), high protein feeding aerobic stacking (CH), low protein feeding aerobic stacking (CL). The stack temperature, and the carbon and nitrogen contents were monitored during composting.

Results The duration of high temperature, NH₄⁺-N content, T value (ratio of final to initial C/N) and seed germination index (GI) are generally used as the judging indices of the maturity of composting. In a short period (14 days), the four indices in the composting of pig manure produced by traditional high protein feeding under static composting condition (MH) were 0 d, 0.43 g/kg, 0.91 and 0, respectively, failed to meet the maturity standard. Those of the pig manure compost produced by high protein feeding under aerobic condition were 5 d, 0.33 g/kg, 0.70 and 0.31, and the T value and GI value failed to meet the maturity standard. The four indices of pig manure produced by low protein feeding in static compost (ML) were 0 d, 0.54 g/kg, 0.81, 0.25, and failed to meet the standard of maturity, while in aerobic compost (CL), the four indexes were 6 d, 0.14 g/kg, 0.57, 0.96.

Conclusions Neither manure produced by high protein feeding pigs under static and aerobic fermentation conditions nor manure produced by low protein feeding pigs under static condition can reach the standard of maturity within 14 days. Only the pig manures produced by low-protein feeding can be decomposed in 14 days under aerobic conditions. Therefore, decreasing protein content in feeding of pigs properly will help the rapid maturity of composting in the downstream of intensive farming.