Solubilization of nonstructural carbohydrates as a function of soaking interval and water temperature in southern forages commonly fed to equids

Abstract

Nonstructural carbohydrates (NSC) play a major role in the diet of equids prone to laminitis or afflicted with metabolic conditions such as insulin resistance. Although the threshold of <10% dietary NSC has been set as a guideline for these horses, the execution of feeding below this limit is not fully understood due to the complexities by which water leaches NSC from plants. A study was conducted to determine kinetic characteristics of NSC and DM solubilization in forages commonly fed in the southeastern USA to ascertain appropriate feeding management practices. Samples (180 g) of 4 hays: alfalfa (Medicago sativa), perennial peanut (Arachis glabrata), and Coastal and Tifton-85 varieties of bermudagrass (Cynodon dactylon) were evaluated in 50°C and 28°C soaking liquor at 0-, 15-, 30-, 60-, 120-, 360-, and 720-min soaking intervals. Bale was defined as a replicate with a minimum of 5 replicates per treatment. Samples were dried, ground, and analyzed for total nonstructural carbohydrates (TNC) using wet chemistry. Nonlinear regression models were constructed utilizing JMP Pro 12 (SAS Inc.) to measure the percentage of TNC and DM remaining after each soaking interval. Significance was set at P < 0.05 to determine the effect of treatment on the regression model. Soaking interval was significant with respect to TNC loss for all hay types except alfalfa which trended toward significance (P = 0.07). Water temperature had no effect on loss of TNC. Solubilization prediction equations were created for each hay. Percentage of remaining TNC was defined by [a + b * Exp (c * t)] where a is the point at which TNC solubilization is complete, b is the potentially soluble TNC fraction, c is rate of solubilization as a function of time, and t is the soaking interval. The grass hays reached maximum solubilization of TNC within approximately 2 h whereas the legumes took approximately 4 h. Percentage of DM remaining was defined by [a * Exp (- b * t) + c * Exp (- d * t)] where a is the point at which DM solubilization rate is reduced, c is the remaining DM that can be solubilized, and b and d are rates of solubilization as a function of time. Regardless of forage type, quality, or maturity, these formulas can be used to design effective soaking treatments to obtain desired TNC concentrations below recommended thresholds.