Total 'shrink' losses, and where they occur, in commercially sized silage piles constructed from immature and mature cereal crops.

Silage 'shrink' (i.e., fresh chop crop lost between ensiling and feedout) represents losses of potential animal nutrients which degrade air quality as volatile carbon compounds. Regulatory efforts have, in some cases, resulted in semi-mandatory mitigations (i.e., dairy farmers select a minimum number of mitigations from a list) to reduce silage shrink, mitigations often based on limited data of questionable relevance to large commercial silage piles where silage shrink may or may not be a problem of a magnitude equal to that assumed. Silage 'shrink' is generally ill defined, but can be expressed as losses of wet weight (WW), oven dry matter (oDM), and oDM corrected for volatiles lost during oven drying (vcoDM). As no research has documented shrink in large cereal silage piles, 6 piles ranging from 1456 to 6297tonnes (as built) were used. Three used cereal cut at an immature stage and three at a mature stage. Physiologically immature silages had generally higher (P<0.01) levels of total volatile fatty acids (especially acetic acid; P=0.01) and total alcohols (P<0.01) than did physiologically mature crops, suggesting higher carbon compound volatilization potential from immature silages. However expressed as WW, oDM and vcoDM, total shrink (as well as from where in the piles it occurred) was little impacted by crop maturity, and whole pile vcoDM shrink was only ~35g/kg. Overall, real shrink losses (vcoDM) of large well managed cereal silage piles were relatively low, and a lower potential contributor to aerosol emissions of volatile carbon compounds than has often been assumed. Losses from the silage mass and the exposed silage face were approximately equal contributors to vcoDM shrink. Mitigations to reduce these relatively low emission levels of volatile organic compounds from cereal silage piles should focus on the ensiled mass and the exposed silage face.