N excretion coefficient based on the whole process of pig production and manure N excretion in China

The present study aimed to improve the nitrogen (N) excretion parameter system applied to pig breeding to accurately calculate the related manure N excretions. Metabolic assessment of full fecal and urine production in the whole process of pig breading (reproduction-weaning-growth-fattening, for a total of 285 days) were performed in 12 breeding sows (Yorkshire×Landrace) and 12 commercial pigs (Yorkshire×Landrace×Duroc). We recorded the feed intake, fecal and urine production, and collected samples every day for moisture and N content evaluation. The collected data were combined with the pig production performance parameters to calculate the pig breeding-associated annual N excretion coefficient. Lastly, we evaluated changes on N excretion and regional distribution of pig-production based on the statistical data and cultivated land area of different provinces (cities) from 2000 to 2018 in China. The results indicated that pigs had significantly different N intake and excretion at different growth physiological stages, being 72.32 and 49.42 g·d^-1 in open days, 55.79 and 45.36 g·d^-1 during early pregnancy, 56.25 and 22.27 g·d^-1 in mid-gestation, 72.41 and 26.36 g·d^-1 in late pregnancy, and 114.28 and 38.84 g·d^-1 during lactation, respectively. In commercial pigs, the N intake and excretion was 22.86 and 10.96 g·d^-1 in weaning, 34.87 and 18.34 g·d^-1 during early growth, 54.67 and 34.50 g·d^-1 during late growth, and 55.15 and 35.79 g·d^-1 during fattening, respectively. Moreover, urinary N excretion was higher than fecal N excretion at each stage. The annual N excretion coefficient of commercial pigs and sows was 9.00 and 11.75 kg·head^-1·a^-1, respectively. From 2000 to 2018, the total N excretion from pig breeding in China increased and then gradually decreased; however, the N excretion per unit pork product decreased every year. The N excretion by commercial pigs accounted for the largest proportion of the total manure N, with an average of 84.03%. Sichuan, Henan, Hunan, and Shandong were the top four provinces with the highest N emission, accounting for 33.67% of the total N emission from pig-production in China, whereas the provinces (cities) with the largest N load per unit cultivated area were Fujian, Guangdong, Hunan, Beijing, and Shanghai. Therefore, we should consider the population structure and the corresponding N excretion coefficient when calculating the amount of N emission from pig breeding, and fully consider the environmental carrying capacity when making development plans.