Digestibility and Glycemic Response of Timothy-Based Haylage and Timothy Grass Hay

Haylage is often fed to horses around the world and may be an appealing forage choice for certain horses due to its low dust content and lower NSC content when compared with hay of comparable species and maturity. The objective of this study was to determine if there were differences in digestibility and glycemic response between hay and haylage of similar quality. Four Thoroughbred geldings (9.3 ± 1.5 yr; 617 ± 40 kg; mean ± SD) were used in a crossover design with 2 dietary treatments over 2 28-d periods. The 2 dietary treatments were second-cutting timothy hay and timothy-ryegrass haylage both fed at 1.5% BW (DM basis). To minimize refusals, one horse was fed at 1% BW (DM basis) for the last 9 d of each period. The hay contained 15% WSC, 0.7% starch, 35% ADF, and 57% NDF, and the haylage contained 9% WSC, 0.8% starch, 39% ADF, and 66% NDF (DM basis). The hay and haylage had similar lignification of the cell wall fraction (lignin/NDF; 9.1% vs 8.4%, respectively). Total fecal collections were conducted during the last 5 d of each period to determine digestibility. Glycemic response to a meal of the assigned forage was conducted on d 22of each period by analyzing plasma for glucose every 30 min for 480 min post-feeding and calculating the area under the curve (AUC). The effect of treatment was analyzed using an ANOVA (SAS Institute Inc., Cary NC) and significance was defined when P < 0.05. The AUC per g of NSC was not different between diets (P > 0.10). Horses had a slower rate of DM intake when fed the haylage meal (10 g DM/min versus 25 g DM/min for hay; P < 0.05) and also had a longer time to peak glucose (P < 0.05). Dry matter digestibility was 58.1% for hay and 50.4% for haylage (P < 0.05). Despite containing a similar degree of cell wall lignification, the hay diet resulted in a greater digestibility of NDF and ADF compared with the haylage diet (P < 0.05). Horses fed haylage had greater fecal moisture than horses fed hay (86% and 76%; P < 0.05) and demonstrated free fecal water. The appearance of free fecal water may have been related to the lower-than-expected fiber digestibility in the haylage diet. More research is needed to determine causative factors in the development of free fecal water in horses.