Experimental Procedures
One hundred sixty crossbred steer calves (initial weight, 600 lb) were used in a 2 X 2 factorial (plus control) experiment. Steers were allotted to 20 pens with 8 steers per pen and 4 pens per treatment. Treatments were as follows:
Carbohydrate and protein sources were combined in five pelleted concentrates. Cattle were fed chopped orchardgrass hay and their respective concentrate as outlined above. Total rations contained approximately 65% hay and 35% concentrate on a dry matter basis. However, concentrates were fed on an amount per head basis and hay was offered free choice to facilitate feeding.
Supplement compositions are in Table 1. All supplements provided 200 mg/head/day of Rumensin.
Steers were fed once daily beginning at 0900 hours. Feed offered was recorded on a daily basis and weigh-backs were taken as necessary.
Feedstuffs were analyzed weekly for DM and feed samples were collected and composited every 14 days. On a monthly basis (every 28 days) composited feed samples were analyzed for dry matter, protein, and fiber.
The trial was 70 days in duration and began on 11/18/99. Initial and final weights were determined using the average weight from two consecutive days. Interim weights were taken every 14 days. All steers were implanted with Synovex-S at the initiation of the trial. Pens (15 X 15 ft) were constructed of metal gates and cable, had slatted floors, and were located in an open-sided barn. There was 22 inches of bunk space per steer.
Daily gain, DM feed intake, and feed efficiency data were collected. Data were analyzed using GLM procedures of SAS. The model contained effects due to carbohydrate source, protein source, the interaction of these main effects and the contrast of the low protein negative control versus others. Pen served as the experimental unit.