Influence of mass of ruminal contents on voluntary intake and digesta passage of a concentrate and a forage diet

To evaluate the influence of mass of rumen contents on voluntary intake and rumen function, five ruminally cannulated steers (500 kg) were fed a hay diet ad libitum in a 5 x 5 Latin square experiment. Mass of ruminal contents was altered by adding varying weights of modified tennis balls to the rumen before the initiation of each experimental period. Treatments consisted of 50 balls with a specific gravity (SG) of either 1.0, 1.1, 1.2, 1.3 or 1.4 and the total weight of the balls was 7.45 kg, 8.50 kg; 9.25 kg, 10.55; and 11.55 kg, respectively. Daily DMI was 5.93, 5.53, 4.98, 4.74, and 4.69 kg for 1.0, 1.1, 1.2, 1.3, and 1.4 SG balls, respectively. Increasing SG of the balls added to the rumen decreased dry matter intake (DMI) and particle passage rate (PPR) (P \u3c .05) in a linear manner. The linear effect on DMI and PPR suggests that physical location of the balls according to their SG in the reticulo-rumen do not appear to directly impeded digesta flow. A second experiment was conducted to evaluate the influence of mass of rumen contents on voluntary intake and rumen function of both forage and concentrate diets. Five ruminally cannulated steers (580 kg) were fed a 70% concentrate (C) or a hay (H) diet ad libitum in a 5 x 5 Latin square experiment. Mass of ruminal contents was altered as in the first experiment. Treatments consisted of 0 balls added to the rumen of steers fed C diet (control), 75 balls with a SG of 1.1 fed a C diet, 75 balls with SG 1.4 fed a C diet, 75 balls with SG 1.1 fed H diet, and 75 balls with SG 1.4 fed H diet. Total weight of the balls was 12.75 and 17.35 kg for the 1.1 and 1.4 SG, respectively. Daily DMI was 15.11, 11.93, 10.65, 6.09, and 5.10 kg for control, 1.1 SG balls fed C, 1.4 SG balls fed C, 1.1 SG balls fed H, and 1.4 SG balls fed H, respectively. Addition of balls the rumen of steers fed the C diet decreased DMI (P \u3c .05), and increasing SG of balls in the C and H diet decreased DMI (P \u3c .01) further. Adding balls to the rumen of steers fed the C diet decreased PPR (P \u3c .05), while increasing SG of balls decreased PPR for both C and H diet. Addition of balls to the rumen of steers fed the C diet decreased (P \u3c 0.01) the proportion of medium (1.1--1.4) and increased (P \u3c .01) the proportion of low (\u3c1.1) functional SG (FSG) digesta particles. Balls added to the rumen of steers fed C diet increased (P \u3c .05) geometric mean diameter of ruminal digesta particle size. Ruminal NH4 and pH levels of steers fed the C diet were decreased (P \u3c .01) with addition of balls, and by increasing mass in the rumen, pH levels decreased further for both C and H diet. The results of this study suggest that density of ruminal digesta can have an influence on voluntary intake of both forage and concentrate diets