Breath ammonia as a bioindicator of protein nutrition in heifers

Abstract The objective of the current study was to determine if breath ammonia excretion could be used as a bioindicator of protein metabolism in heifers. Four Holstein heifers distributed in a 4 × 4 Latin Square design were fed diets containing 9, 12, 15 and 18% crude protein (CP). Breath ammonia (BA) excretion and serum urea nitrogen (SUN) levels were evaluated at 6 a.m., 12 p.m., 6 p.m. and 12 a.m. Urinary urea nitrogen (UUN) excretion was measured daily. The BA excretion increased linearly with dietary CP levels. The correlations between BA excretion and SUN levels (0.67) and between BA excretion and UUN excretion (0.55) were high. In conclusion, BA excretion has the potential to be used as an indicator of protein nutrition.