The application of low crude protein wheat-soyabean diets to growing and finishing pigs - 2. The effects on nutrient digestibility, nitrogen excretion, faecal volatile fatty acid concentration and ammonia emission from boars
Leek, A.B.G.; Callan, J.J.; Henry, R.W.; O'Doherty, J.V.
Irish Journal of Agricultural and Food Research 44(2): 247-260
Diets containing 132, 152, 183 and 206 g/kg crude protein (CP) were fed to growing and finishing boars to evaluate the effect on nutrient digestibility, N balance, faecal volatile fatty acids (VFA) and ammonia-N (NH3-N) emission. Dietary CP concentration was adjusted by altering the ratio of wheat:soyabean meal. Lysine, threonine, tryptophan and total sulphur-containing amino acids were included in all diets at concentrations equivalent to that in the highest CP diet. All diets were formulated to provide 9.7 MJ/kg of net energy. Urine and faeces were collected from 16 boars (4 boars per treatment) housed in metabolism crates. Collections were performed at 72, 80 and 87 kg live weight. NH3-N emission was measured over 10 days using a laboratory scale procedure. Reducing the concentration of dietary CP decreased N intake (linear, P < 0.01), the excretion of urinary N, ammoniacal N and total N (linear, P < 0.001; cubic, P < 0.001) and the emission of NH3-N (linear, P < 0.001; cubic, P < 0.01). Total N excretion and NH3-N emission decreased 8.7% and 10.1% per 10 g/kg reduction in dietary CP concentration between 205.6 and 131.9 g/kg, respectively. There was no interaction between dietary CP concentration and collection period. N balance differed between the collection periods and less NH3-N was emitted at 87 kg than at 72 kg. Decreasing dietary CP reduced faecal VIA concentration (linear, P < 0.05) and the molar proportions of acetic and butyric acids (quadratic, P < 0.01).