Efficiency of mastication in relation to hay intake by cattle.

Four dry Holstein cows and four hay levels (50, 75, 100 and 125% of NRC-recommended dry matter intake) were used to study the efficiency of mastication and rumination in relation to hay intake. The experimental design was a 4 x 4 Latin square with 7-day periods. Increased hay levels resulted in increased rumination time, eating time, number of rechewings and boluses. When corrected for cell wall constituents (CWC) intake, rumination time decreased as level of hay intake increased, while eating time increased. Consequently, total chewing time per kilogram CWC intake did not differ (P less than .05) with hay level. Results indicate that ingested roughages required a constant amount of trituration either by eating or by rumination. The amount of each fecal particle size fraction retained by four different sieve sizes, and the total of these larger particles (above .3 mm), did not differ (P greater than .05) among hay levels. Results suggest that acceptability of indigestible particles by the reticulo-omasal orifice was not affected by the amount of hay intake.