BS in Dairy Science
Dairy Science Department
The objective of this study was to determine any trends in odor evaluations and gas emissions of manure samples in heifers fed high/low concentrate and high/low forage diets. Heifers (n = 8) were enrolled randomly in a split plot design with diet type (high concentrate vs. low concentrate) as the whole plot and forage quality (4 different levels of corn stover within each diet type) as sub-plots in a 4-period (21d) 4X4 Latin square design. Total collection of urine and feces was performed on days 18-21 of each period. The feces to urine ratio (F:U) was determined on days 18 & 19, and used to collect a 200g of manure sample to place in a multi-chamber steady-state gas emission detection system. Gas concentrations were measured every 20min over a 24hr period.7.0L odorous exhaust sweep air was taken from each chamber of the system after 1hr, and presented to trained panelists within 7hrs of manure collection. Panelists performed subjective odor evaluations for hedonic tone (quantified using 22-unit scale) and intensity (Labeled Magnitude Scale method 0-100) during their evaluation. A Triangular Forced-Choice method was used to determine detection threshold (DT) & recognition threshold (RT) of each sample. A significant difference between CO2, CH4, and NH3 emissions were found among the 8 diet types. CO2 emissions were significantly higher in the LC diet, and a positive correlation between CO2 & NH3 emissions was found. There was a linear decrease in CH4 emissions as % CST in LC diets increased. The highest average odor emission (8.58 OU m-2 sec-1) was found in the LC diet with 0% CST; while the lowest average odor emission (5.01 m-2 sec-1) was observed in the LC diet with 60% CST. Also, the mass of feces from HC heifers was 50% less than LC heifers, but HC urine excretion was 2.84 times higher, making the total manure excretion 22.7% higher in HC heifers than LC heifers (a factor that could have contributed to the odor and gas emission rates). In the end, this study showed a notable association between diet type and resulting odor and gas emissions.