Effects of storage-handling methods on nutrient analysis of fresh-forage samples

Forage low in nonstructural carbohydrates (NSC) is recommended for insulin dysregulated (ID) horses, indicating the importance of an accurate forage analysis. However, it remains to be fully understood how handling forage samples pre-analysis impacts nutrient values. The objective of this study was to compare the effect of fresh-forage storage-handling methods: microwave-oven (MO; 9kw; 70s then stored at -20℃), room temperature (20℃), 3℃, -20℃, and -80℃. Subsamples collected from a mixed-grass pasture and a ryegrass plot were analyzed for crude protein (CP), water soluble carbohydrates (WSC), ethanol soluble carbohydrates (ESC), starch and NSC (starch and WSC). Forage samples were stored for two different time periods (24h vs 1wk) prior to being shipped on ice to a commercial laboratory for wet chemistry (WC) and near-infrared spectroscopy (NIR) analysis. Mixed grass stored at RT showed a reduction in WSC (P=0.009), ESC (P=0.001) and NSC (P=0.006) from 24h to 1wk. Similarly, ESC and starch of the ryegrass and CP of mixed grass decreased after 1wk, but only when stored at -80℃ (P=0.007; P=0.001; P=0.02). Additionally, over time, CP of ryegrass and ESC of mixed grass became higher when stored at -20℃ and MO, respectively (P=0.02; P=0.03). From this study, in order to limit metabolic changes and provide accurate nutrient composition results, practically fresh forage that cannot be quickly analyzed should be transported on ice post collection to a storage location then immediately refrigerated where it can be kept up to one week prior to being shipped on ice for analysis.