To evaluate the chewing activity of ruminant feeds, four Holstein steers (average body weight 742±15 kg) were employed. Experimental feeds were four roughages (NH 3 -treated rice straw, alfalfa hay, corn silage, orchard grass hay) and four concentrate ingredients (cotton seed hull, beet pulp pellet, barley grain, oat grain). Regarding palatability for each experimental feeds which was overviewed during the adjustment period, animals were fed roughages alone, but with 50% NH 3 -treated rice

more »

... (NH 3 -RS) for concentrate ingredients. Therefore, all the data for concentrate ingredients was derived by extracting the result per unit obtained from steers fed NH 3 -RS alone. The experiment was conducted using a 4×4 Latin square designs for roughages and concentrate ingredients. Experimental feeds were fed during a 10 d adaptation and 2 d chewing data collection during each experimental period. Animals were gradually adjusted to the experimental diet. Dry matter intake (DMI) was restricted at a 1.4% of mean body weight (10.4 kg DM/d). Time spent eating and eating chews per kilogram of DMI were greatest for beet pulp pellet, and lowest for barley grain (p<0.05). Time spent rumination per kilogram of DMI was greatest for NH 3 -RS, cotton seed hull and orchard grass, but rumination chews were greatest for cotton seed hull and orchard grass except NH 3 -RS (p<0.05). Roughage index value (chewing time, minute/kg DMI) was 58.0 for cotton seed hull, 56.1 for beet pulp pellet, 55.5 for NH 3 -RS, 53.1 for orchard grass hay, 45.9 for corn silage, 43.0 for alfalfa hay, 30.0 for oat grain, and 10.9 for barley grain. The ratio of rumination time to total chewing time (eating plus ruminating) was about 72% for the roughages except corn silage (66.9%), and followed by cotton seed hull (69.5%), and ranged from 49.5% to 52.9% for other feeds. Higher percentages of rumination in total chewing time may be evidently indicate the characteristics of roughage. Therefore, this indicate that the chewing activity of concentrate ingredients can be more fully reflects by the ruminating time than total chewing time (RVI), although it is reasonable to define the RVI for roughages. (Asian-Aust. J. Anim. Sci. 2002. Vol 15, No. 7 : 968-973)