Odor Evaluation and Gas Emission from Manure of Dairy Heifers Fed High/Low - Forage Quality and High/Low-Concentrate Diets

A heifer feeding trial evaluated the impact of high/low forage quality and high/low concentrate level nutrient-balanced diets on simultaneous odor and gas emissions from the manure. Gas concentration was determined using an infrared photoacoustic analyzer over a 24-hour period using a steady-state flux chamber setup containing urine:feces as-excreted from eight individual heifers. Odorous air samples were collected from chamber headspace and evaluated by six human assessors for pleasantness, intensity and detection threshold using a forced-choice dynamic olfactometer. Ammonia emission ranged from 0.64 to 3.94 mg NH3 cm d across diets. Average ammonia emission from the low concentrate (80% forage) diets (2.11 mg NH3 cm d) was larger than the high concentrate (20% forage) diets (1.69 mg NH3 cm d), but not significantly different. Carbon dioxide emission was significantly higher (p= 0.0143) in the low concentrate diets. There was a linear increase of methane emission as reduced quality forage (corn stover) was increased in the low-concentrate diet (p = 0.030). Nitrous oxide emissions were similar and low in all diets. Highest average odor emission (8.58 OU m sec) was from the low concentrate, high forage quality (80% corn silage) diet while lowest emission (5.01 OU m sec) was measured when forage quality was reduced (32% silage; 48% stover). Odor emission tended to be reduced with lower quality forage diets, but with no significant difference. The volume of feces produced from the high concentrate diet was about half that from the low concentrate diet heifers. But total manure produced by the high concentrate diet heifers was 23% higher due to increased urine production.