Relationship between Voluntary Intake of Timothy Hay in Dairy Cattle and Chemical Composition, Retention Time in the Rumen, Digestibility and Digestion Rates

Three experiments were carried out to study the effects of feed characteristics on voluntary intake that was measured as dry matter intake (DMI) using 4 dairy cows offered timothy hay ad libitum. The digestibility depending on the chemical composition of timothy hay was determined using the total collection method in sheep, while the rate of fiber degradation in the rumen was calculated by the in vitro method. Mean daily DMI and DMI per metabolic body weight of 4 types of timothy hay ranged from 6.5 to 9.1 kg/day, and 56.9 to 78.8 g/kg0.75, respectively. The daily DMI of timothy hay by dairy cows was closely related to the organic b fraction (Ob), sum of organic cellular contents and organic a fraction (OCC+Oa), and content of acid detergent lignin (ADL). The daily DMI could be predicted from the following regression equations; DMI = -0.18 x Ob + 19.5 (r=0.993), DMI = -0.50 x ADL + 12.1 (r=0.997), DMI = 0.19 x (OCC+Oa) -1.6 (r=0.993). In addition, the daily DMI of timothy hay by dairy cows was also closely related to the retention time in the rumen, digestibility depending on the chemical composition and rate of degradation of fibers in the rumen.