Effect of different quality wheat dried distiller's grain solubles (DDGS) in pig diets on composition of excreta and methane production from faeces and slurry

This study was conducted to investigate the effects of the incorporation in pig diets of 25% of ten different wheat dried distiller's grain solubles (DDGS) from biofuel production, on (i) the excretion of organic matter (OM), nitrogen (N) and carbon (C), and (ii) on the potential of methane (CH4) emission from effluents (faeces and slurry). Eleven experimental diets were formulated: a control diet mainly based on cereals and soybean meal, and ten experimental diets obtained by adding to the control diet 25% of one of the ten samples of DDGS. The DDGS differed by their origin and the process of biofuel production. They were classified according to a colour score used as an indicator of processing conditions. The ultimate methane potential of effluents (B0, expressed in L CH4/kg OM) was measured for each diet in anaerobic storage conditions over 100days. The addition of DDGS to pig diets increased the amount of faeces excreted by 27 to 50% and the amount of slurry excreted by 7 to 50%, compared to the control diet. The OM excretions in faeces and in slurry were significantly increased by 59% and 75% respectively, with wheat DDGS inclusion, compared to the control diet. As for total N and C excretory patterns, the addition of wheat DDGS increased their excretions by 65% and 54%, respectively, compared to the control diet. The results indicated that the partitioning of N was shifted from urine to faeces with the inclusion of fibre from wheat DDGS. B0 values measured on faeces and slurry were respectively in a range from 202 to 294 and from 278 to 368L CH4/kg OM. On average, B0 values were lower for the effluents from the DDGS diets compared to the effluent from the control diet. The type of DDGS also affected the B0, with lower values obtained for dark compared to medium or light DDGS. When methane emission was expressed per pig and per day, potential productions for slurry and faeces from the control diet were 51 and 68L/day, respectively. On average, the values were significantly higher, by about 40%, for slurry and faeces from DDGS diets, with 72 and 98L/day, respectively. It was concluded that the heating process of DDGS may reduce the methane production potential of their indigestible OM. However, because of the increased OM excretion, incorporating DDGS in pig diets increases the potential methane production per pig produced.