Abstract
The effect of dietary crude protein (CP) level on ammonia (NH(3)) emissions from slurry from lactating Holstein-Friesian cows was studied. Twenty-four-hour total collections of faeces and urine were made from 24 lactating Holstein-Friesian cows fed four total mixed rations containing 141, 151, 177, and 201 g CP/kg DM (6 cows/diet). The collected urine and faeces from each cow were combined to form 2 kg duplicate slurry samples (weight/weight; fresh basis) according to the proportions in which they were excreted. NH(3) emissions from the slurry samples were measured, during 0-24 and 24-48 h intervals in six open-circuit respiration chambers maintained at two temperatures (8 or 18 °C). NH(3) emissions for the 0-24 and 0-48 h intervals, as well as the average daily emissions, increased linearly with increasing dietary CP level. Increasing the temperature from 8 to 18 °C positively affected NH(3) emissions, but only for the 0-24 h interval. In situations where direct measurements are impossible, NH(3) emissions from slurry can be predicted accurately using equations based on dietary CP level supported by either urinary nitrogen, faeces nitrogen, or both. In summary, increasing dietary CP level linearly increased average daily NH(3) emissions from slurry, with a 5.4 g increase for each 10 g increase in dietary CP.