Comparison of collection methods for determination of forage nutritive status

Forage samples were collected from pastures amended with one of five biosolids (municipal sludges) and fertilizer treatments (year one) or eleven treatments in year two. Forage samples were collected six times during each year, once every 28 d, beginning in mid-June. Two methods of forage collection were compared, the cage method and the transect method. The transect method involved collecting samples at different areas of a pasture to more closely mimic what the animals appeared to consume. In year one, forage samples obtained using the cage method were collected from permanent cages (approximately 2 m diameter) randomly placed, but then fixed in position in each pasture. In year two, the cages were randomly moved to new spots following each sampling and mowing. During year one, copper (Cu), zinc (Zn), and iron (Fe) concentrations differed (P<0.05) by collection method several times, with microelement concentrations from cage samples routinely being higher than from transect samples. Differences were observed at fewer sampling times during year two for Cu and Fe, but Zn concentrations differed at each sampling time. The macroelements followed a similar pattern, with more differences due to collection method observed during year one than year two. The in vitro organic matter digestibility (IVOMD) and crude protein (CP) results suggest an effect of increasing maturity for the transect samples contributing to the differences observed in collection methods in year one. When forage collection methods differed in forage mineral concentrations, cage samples gave routinely higher units but this difference was reduced when cages were moved to new locations following sampling.