Estimates of the amount of variation (i.e.,standard deviations and ranges) in nutrient composition of common feeds are readily available from some national feed testing labs,however,estimates of variation for feeds within a farm are needed to determine appropriate feed sampling and ration re-formulation schedules.We conducted a large national survey to determine within farm variation for some common feeds.On average within farm variation for crude protein (CP) and neutral detergent fiber (NDF) was 2 or 3 times less than variation in the national population.Within a farm,substantial day to day variation in dry matter,NDF,CP and starch was observed for corn silage and haycrop silage indicating that samples should be taken over several days and those results averaged for diet formulation purposes.In some cases,day to day variation was as great as month to month variation.The concentrations of NDF,but not CP,in high moisture corn,distillers grain,and brewers grains varied almost as much as NDF concentrations in some forages indicating that these feeds should be sampled on a regular basis.
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