Feed Intake and Gains of Beef Cattle as Affected by Source and Level of Nitrogen in High-Energy Rations

Abstract

Feed intake and gains were measured in an experiment using 20 individually fed grade Angus receiving two levels and two sources of nitrogen in ground-pelleted rations containing 25% low quality grass hay as the only roughage. The experiment was patterned after Lucas' extra-period Latin-square change-over design using 28-day evaluation periods following 14-day adjustment periods. Rations St (1) and Su (2) were high-energy low-protein treatments providing a comparison of corn starch and cane sugar as important sources of energy; rations StC (3) and SuC (4) were high-energy high-protein treatments formulated by adding protein to rations St and Su by replacing part of the starch and sugar with cottonseed meal; and ration U (5) was formulated by adding urea to ration St at the level necessary to make the protein equivalent equal to rations StC and SuC. Body weight and metabolic body size had no appreciable effect on feed intake within the range of animal weights in this experiment. Animals when on higher protein or protein equivalent gained faster, more efficiently, and consumed more feed than when on low protein. There was no significant difference between the gains while the animals were receiving the low-protein rations. There was more increase in feed intake when cottonseed meal was added to the sugar ration than when added to the starch ration, although without added protein feed intake of the sugar ration was lowest. Daily gains (lb.) for rations (1) through (5) were: 0.02^a; 0.02^a; 1.73^b; 2.10^bc; and 2.26^c; and daily feed consumptions were: 11.5^b; 9.5^a; 17.3^d; 17.7^d; and 15.1^c, (figures with the same a, b or c superscript in each case are not significantly different). Consumption of rations intended to be high-energy and low-protein was very low indicating an effect of protein level on voluntary feed intake. The ration supplemented with urea supported the fastest and most efficient gains. Ruminal protozoal distributions were normal except for animals when fed ration St in which the protozoan Epidinium ecaudatum was found in large numbers; animals when fed StC contained unusually high numbers of species of Diplodinium; and for low populations of the holotrich Isotricha in all rations fed.