Supplemental fat and ionophores in finishing diets: feedlot performance and ruminal digesta kinetics in steers
1993
Clary, E.M. | Brandt, R.T. Jr | Harmon, D.L. | Nagaraja, T.G.
One feedlot trial (116 d; 192 steers) with a factorial arrangement of treatments was conducted to determine effects of supplemental fat and ionophores in corn-based finishing diets. Factors were level of fat (0 or 4% tallow) and ionophore type (none [N], lasalocid [L], monensin plus tylosin [MT], or daily rotation of L and MT [LMT]); L, M, and T were fed at 31, 25, and 10 ppm (DM basis), respectively. Fat and ionophore interacted for DMI (P < .10), ADG (P < .01), and gain:feed G/F, P < .05). Compared with 0%-fat diets, 4% fat decreased (P < .005) DMI by steers fed MT by 8.9%. In 0%-fat diets, MT increased (P < .05) ADG and G/F compared with N or L; however, this increase was negated or reversed in 4%-fat diets. Fat and ionophore interacted (P < .16) on dietary NE concentration. In the 0%-tallow diet, MT increased NEm and NEg by 5.1 and 7.0%, respectively, but MT had no effect on NE concentration of the 4%-tallow diet. Alternate feeding of L and MT did not increase animal performance above that of separate, continuous feeding. Six ruminally fistulated steers were used in a metabolism study to evaluate potential mechanisms underlying the interactions observed in the feedlot trial. Treatments were the same as the feedlot trial, except that LMT was not included. Ruminal digesta kinetics were not altered (P > .30) by the addition of fat or ionophores to the diet. Fat and ionophore interacted (P < .05) for molar proportions of ruminal acetate and propionate. Acetate was decreased (P < .05) and propionate was increased (P < .05) by ionophore addition to the 0%-fat diets; however, when 4% fat was fed, neither L nor MT affected acetate or propionate. These results suggest that the response of finishing cattle to ionophores may be altered by fat supplementation, perhaps in part as a result of negative associative effects between these additives on the end products of ruminal fermentation.
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