Influence of Lasalocid and Monensin Plus Tylosin on Comparative Feeding Value of Steam-Flaked Versus Dry-Rolled Corn in Diets for Feedlot Cattle

Two trials were conducted to characterize the differences in utilization of dry-rolled and steam-flaked corn in a growing-finishing diet for feedlot cattle supplemented with and without ionophores. Ionophore treatments were: 1) no ionophore, 2) 33 mg/kg monensin sodium plus 11 mg/kg tylosin and 3)33 mg/kg lasalocid sodium. In trial 1, treatment effects on feedlot performance were evaluated in a 239-d growing-finishing trial involving 180 crossbred steers (approximately 25% Brahman with the remainder represented by Hereford, Angus, Shorthorn and Charolais breeds in various proportions) with an average initial weight of 153 kg. In trial 2, treatment effects on characteristics of digestion were evaluated using six steers of similar breeding and background to those used in trial 1, with cannulas in the rumen and proximal duodenum. There were no interactions between corn processing and ionophore supplementation (P>.20). Average daily gain was not affected by steam-flaking as opposed to dry-rolling, however, feed intake was decreased 5.4% and feed conversion was improved 6.8% (P<.01). Steam-flaking increased the estimated net energy value of the diet 7.7% and 8.5% for maintenance and gain, respectively (P<.01). Steam-flaking increased the digestibility of starch 6.6% (P<.01). Steam-flaking increased ruminal molar concentrations of propionate and decreased acetate:propionate ratio and estimated methane production (P<.10). Both monensin-tylosin and lasalocid resulted in reduced feed intake (12.3 and 6.5%, respectively, P<.01). Feed conversion was improved 5% by the inclusion of ionophores in the diet (P<.01), with differences between ionophores being small. Daily weight gain tended to be lower for monensin-tylosin supplemented steers (P<.10). Inclusion of ionophores in the diet resulted in relatively minor changes in site and extent of digestion. It was concluded that steam-flaking increased the net energy value of corn 13.4% for maintenance and 14.2% for gain. Improvements in net energy value of corn were due largely to enhanced starch digestibility, particularly post-ruminal Response to steam-flaking may not vary appreciably in the presence of supplemental ionophores.