112 Effects of storage-handling methods on nutrient analysis of mixed-grass pasture samples

Abstract

Forage should be the basis of any equine diet, even for those with insulin dysregulation (ID). Fresh and preserved forage low in nonstructural carbohydrates (NSC) is recommended for ID animals, indicating the need for an accurate forage analysis. It remains to be fully understood how handling fresh forage samples pre-analysis impacts nutrient values. The objectives of this study were to compare 5 pasture sample storage-handling methods, analyzed after 24h and 1wk, on various nutrients including crude protein (CP), water soluble carbohydrates (WSC), ethanol soluble carbohydrates (ESC), starch and NSC. In October 2022, forage samples were manually harvested to ground height between 0800 and 0900 from a mixed-grass pasture after a rest period. Subsamples were mixed to create triplicate samples for analysis at both time periods (24h vs 1 wk) and the following 5 storage-handling methods: microwave-oven (70s then stored at −20°C; MO), room temperature (RT), 3°C, −20°C, and −80°C, totaling 30 samples. All forage samples were shipped on ice to a commercial laboratory for wet chemistry and NIR analysis (Equi-Analytical, Ithaca, NY). Data were analyzed using 2-way ANOVAs in JMP with fixed effects of storage method, time and storage by time interactions as well as storage-handling method by laboratory analysis method and method by storage interactions.Statistical significance was declared at P ≤ 0.05. All data reported are from wet chemistry analysis as there were no significant differences between the 2 analysis techniques. Storage by time interactions were statistically different for some nutrients measured from the mixed grass when stored at RT. Specifically, the WSC (9.2 ± 0.4% DM vs. 5.4 ± 0.9% DM; P = 0.009) and ESC (5.4 ± 0.4% DM vs. 3.6 ± 0.6% DM; P = 0.001) content decreased from 24h compared with 1wk. The remaining storage-handling methods of MO, 3°C, −20°C, and −80°C, however, showed no statistical differences across time for WSC, Starch or NSC indicating these methods were appropriate for storing forage for this time. A decrease in CP content from 24h compared with 1wk was, however, shown when stored at −80°C (12.7 ± 0.6% DM vs. 11.2 ± 0.3% DM; P = 0.02), yet no other statistical differences in CP were detected. These results demonstrate that samples kept at RT or −80°C for one week before nutrient analysis may not accurately represent the nutrient content of the forage. Storage-handling method and time did affect the nutrient content of fresh forage thus, samples should be either immediately dried, kept at 3°C, or frozen (−20°C) preceding analysis.