Operation effects of dead pigs composted with swine manure in winter

Abstract: Composting is an environment-friendly method for animal carcass disposal, but in China there is a lack of literature on mortality composting, which is scarcely applied in livestock industries by far. This pilot experiment was conducted to investigate the disposal load and the feasibility of composting swine mortalities in northern parts of China during winter. Composting bins with capacity of 0.95 m3 were used to dispose nursery mortalities, and on-farm swine manure and the available agricultural waste (corn stalk) were collected and mixed according to the requirements of manure composting. Two treatments of double-layer carcasses and single-layer carcasses, and no carcass control were designed. There were twelve composting bins, among which four were allocated to each treatment and control groups. Inside each composting bin of the treatment groups, dead nursery pigs with weight of 4.6-21.4 kg each were placed in layer (s), each layer contained 3 dead animals with total weight of 28.0-30.0 kg. For the single-layer treatment, dead nursery pigs were put in the middle of each bin with the upper and lower parts filled with mixture of swine manure and corn stalk. Inside the composting bins of double-layer treatment, 30 cm mixture was placed between two layers of dead nursery pigs, with mixture beneath and over dead pig layers too. The composting bins were aerated with ventilation rate of 100 L/(m3·min), the experiment lasted for 8 weeks from December 2012 to January 2013 in Beijing. The results showed: the daily ambient temperatures ranged from 2.7℃ to -11.2℃, with the valley value of -17.8℃ during the entire experimental period. The daily average temperatures inside composing bins exceeded 50℃ within 3-5 d, and the daily average temperatures inside composting bins kept above 50℃ for 32 and 23 d for the double-layer and single-layer treatment groups respectively, which could secure pathogen inactivation and meet the non-hazardous requirement of national standards. No significant difference in degradation rates was found between single-layer and double-layer carcasses composting, and the average degradation rates after 6 w and 8 w composting were 93.6%±3.5% and 96.8%±0.8%, respectively, only small portion of skeletons of the carcasses was left. Therefore, dead swine composting with animal manure is feasible, and the composting bin with height of 1m could disposal two-layer dead nursery pigs simultaneously with the total mass of 58 kg. The pH value of the composting mixture varied in the range of 7.9 to 8.6. Organic matter and total carbon contents of the composting mixture declined with time, and turned to be 47% and 27% respectively at end of experiment. However nitrogen content showed different variation trend, it increased with time and reached 2.9% after 8 w composting, and nitrogen contents of double-layer and single-layer treatments increased by 8.9% and 3.7% from their control basement, respectively. Since the substrate used for swine carcasses composting in this study was the same as swine manure composting, carcasses composting can be incorporated into swine manure composting system. The combined system can operate all the year round, even in the northern part of China.