Effects of physical treatments on the resistant starch content and in vitro organic matter digestibility of different cereals in horses

Samples of some cereals (corn, barley, and oats), whole (W) or subjected to flaking (F), rolling (R) and extrusion (E) were collected from different horses feed industries. Feed samples were analyzed for their proximate composition and fibrous fractions by Van Soest procedure. The total starch content (TS) was determined directly by liquid chromatography (TS1) and as sum of resistant and non-resistant starch using a specific enzymatic kit before the spectrophotometric reading (TS2). In vitro organic matter digestibility (OMD) by pepsin-cellulase technique was also estimated. The content of resistant starch was low in the cereals (on average 2.0% of the total starch), except for the whole corn samples. TS1 values were lower than TS2, particularly at lower starch levels. The in vitro OMD values ranged from 66.8% (whole white oats) to 95.7% (flaked corn). The effects of the physical treatments on the in vitro OMD were variable among cereals. The in vitro OMD of flaked white oats was lower with respect to whole and rolled grain. In corn and barley samples the physical treatments did not change the in vitro OMD values. Using the step-wise multiple regression method for all the chemical parameters, in vitro OMD of the cereals could be predicted by ADF content (R2 = 0.986; RSD = ± 1.2%). Other parameters (CP, lipids, lignin and total starch) gave little improvement in predicting in vitro OMD when included in the model.