Dietary protein affects nitrogen excretion and ammonia emission from slurry of growing-finishing pigs

The effects of dietary protein on nitrogen excretion and ammonia emission from slurry of growing-finishing pigs were studied both in vitro and in a pig house. The three diets had similar contents of NE, minerals, vitamins and ileal digestible lysine, methionine + cystine, threonine and tryptophan, but differed in CP content (16.5, 14.5 and 12.5%). In the balance experiment, 18 castrated males of about 55 kg body weight were allotted to the three diets. The experiment lasted 9 weeks, which were divided into three 3-week periods. In each period, urine and faeces were collected separately for 7 days in metabolism cages and mixed as slurry. A sample of this slurry was placed in a laboratory system to measure ammonia emission for 7 days. In the barn experiment, 216 pigs were housed in three compartments and fed the experimental diets. Ammonia emission was measured directly from the compartments for 7 days during each of the 3-week periods. There was no effect of dietary CP level on faecal nitrogen excretion. Urinary nitrogen excretion and slurry pH decreased when dietary CP decreased. Both balance and barn experiments showed similar effects of dietary CP on ammonia emission from slurry. Ammonia emission was reduced by 10-12.5% for each percent decrease in dietary CP. It is concluded that lowering dietary CP and supplementing essential amino acids while maintaining normal growth rate reduces urinary nitrogen and ammonia emission from the slurry of growing-finishing pigs. (C) 1998 Elsevier Science B.V. All rights reserved.