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Dynamics of offensive gas-phase odorants in fresh and aged feces throughout the development of beef cattle.

Livestock odors are largely caused by several groups of volatile organic compounds (VOC), including sulfur-containing compounds, VFA, and phenols and indoles. Throughout the growth stages of cattle in the nursery and feedlot, distinctly different diets are formulated to meet the changing requirements of the animal. Because diet composition and manure management are 2 major factors affecting odor emissions, it was assumed that changes in diet composition along the development of calves would affect VOC emissions from fresh and stored manure. In this study, the dynamics of gas-phase VOC in feces from 6 Holstein-Friesian bull calves were followed at 5 ages: 1 to 5 wk (stage I), 6 to 8 wk (stage II, before weaning), 9 to 14 wk (stage III, after weaning), and 15 to 36 wk (stages IV and V). The CP content of the formulated diet decreased from 23.0 to 13.9%. Samples of fresh feces were incubated under either aerobic or anaerobic conditions for 21 d. The VOC were analyzed from the feces headspace by solid-phase microextraction, followed by gas chromatography-mass spectrometry. Distinct changes in gas-phase VOC were observed in fresh and aged feces from calves at different ages. Semiquantitatively (based on comparative peak area counts), the following trends were observed: 1) S-containing compounds were the least dominant in fresh feces at the age of 2 wk (stage I), whereas VFA esters were the most dominant. 2) At the age of 7 wk (stage II), 1 wk before calves were weaned, feces seemed to be the most offensive, presumably because of the difficulty of synchronizing the requirements of the animal and the diet formulation during this stage of rapid development. 3) The VOC decreased during storage of feces under aerobic conditions but significantly increased at all 5 life stages during storage under anaerobic conditions. This study demonstrates that life stage and manure management affect odor emissions from beef fattening operations. Incorporation of the age and diet of calves in odor modeling could improve annoyance predictions.