Effect of level and type of fat on subacute acidosis in cattle fed dry-rolled corn finishing diets

Five experiments were conducted to determine the effect of fat addition to dry-rolled corn (DRC) finishing diets on subacute acidosis. In Exp. 1, five ruminally fistulated steers (410 +/- 12 kg BW) were used in a 5 X 5 Latin square design. Treatments consisted of 0, 2, 4, 6, or 8% tallow added to a 50% fine-ground corn: 50% dry-rolled wheat basal challenge diet and dosed intraruminally as an acidosis challenge. Area below pH 6 was determined to quantify the total decrease in ruminal pH over a 24-h period. Area below pH 6 responded quadratically (P < .05); greatest time below pH 6 occurred with diets containing 2, 4, and 6% tallow. In Exp. 2, six ruminally fistulated steers (527 +/- 47 kg BW) were used in a 6 X 6 Latin square design and intraruminally dosed with 0, 4, 6, or 8% tallow or 4 or 8% yellow grease added to a 50% fine-ground corn:50% dry-rolled wheat basal challenge diet. Area below pH 6 responded quadratically for both tallow (P = .10) and yellow grease (P < .05) and was greatest for steers dosed with 4% tallow or yellow grease and decreased as tallow or yellow grease increased from 4 to 8%. Experiment 3 was a metabolism study using six ruminally fistulated steers (469 +/- 68 kg BW) in a 6 X 6 Latin square design. Cattle were fed a DRC finishing diet containing 0, 4, 6, or 8% tallow or 4 or 8% yellow grease. Dry matter intake, ruminal fluid pH, total ruminal VFA, in situ rate of starch digestion, and estimated ruminal starch digestion were not affected (P > .10) by fat addition. Experiments 4 and 5 were combined and used 120 individually fed steers (274 +/- 26 kg BW) in a randomized complete block design. Treatments consisted of tallow or acidulated soapstock added at 0, 2, 4, 6, 8, or 10% of the DRC diet. Dry matter intake (linear, P < .01) and DMI variation (linear, P < .10) were reduced with increasing fat when cattle were consuming 85 and 92.6% concentrate diets during grain adaptation. In the finishing phase, DMI, ADG and gain/feed decreased (linear, P < .01) as fat increased. We conclude that adding fat to DRC finishing diets does not reduce subacute acidosis.