Changes in Chemical and Fatty Acid Composition of Timothy Hay from Field to Bale and During Storage

Pasture contains more protein, fat, and omega-3 fatty acids (FA) than hay, but it is unclear when these losses occur during hay production and storage, and how extensive they are. The objective of this study was to measure changes in the chemical and FA compositions of timothy hay around harvesting and through 3 mo of storage. Four timothy hay fields were representatively sampled the day before harvest, 3 d after harvest while drying in windrows, and the day before baling. Bales of hay produced from the 4 fields were sampled on the day of baling and monthly for 3 mo while stored under cover at the hay production facility. All samples were sent to commercial laboratories for wet chemistry analysis of chemical composition (Dairy One, Ithaca, NY) and FA composition (OmegaQuant, Sioux Falls, SD). Concentrations of nutrients were corrected for dry matter concentration. Data were analyzed using a repeated measures ANOVA with sampling time as the fixed effect. Concentrations of crude protein, starch, and fat were greatest in preharvest samples, decreased during drying in windrows, and then stayed the same through 3 mo of storage (P < 0.05). The drying process decreased crude protein concentrations to 83% of preharvest values and fat to 77% of preharvest values. Alpha-linolenic acid was the predominant FA in all samples (mean ± SE: 44 ± 3% of total FA), followed by palmitic acid and linoleic acid (both 19 ± 1% of total FA). Total omega-3 and omega-6 FA concentrations were greatest in preharvest samples and lowest in baled hay (P < 0.05). Baled hay contained 54% of preharvest concentrations of omega-3 FA and 67% of preharvest concentrations of omega-6 FA. The ratio of omega-6 to omega-3 FA did not change across all sampled time points (P > 0.05). In this study, most of the nutrients that decreased were lost while drying in windrows. Storing hay in a covered location for up to 3 mo does not appear to further affect these nutrient losses.

Fowler, A.L., and J.D. Pagan. 2025. Changes in chemical and fatty acid composition of timothy hay from field to bale and during hay storage. Journal of Equine Veterinary Science 148:105554.