EFFECT OF FREQUENCY OF SUPPLEMENTATION AND PROTEIN-CONCENTRATION IN SUPPLEMENTS ON PERFORMANCE AND DIGESTION CHARACTERISTICS OF BEEF-CATTLECONSUMING LOW-QUALITY FORAGES

Three experiments evaluated whether effects of altered frequency of su pplementation on forage use and cow performance depended on supplement CP concentration and(or) grain type when fed to cattle eating low-qua lity forages. All experiments included supplementation frequency (dail y = 7x; three times weekly = 3x) as one factor in a factorialized arra ngement of treatments. In Exp. 1 and 2, the second factor was suppleme nt CP concentration (10, 20, 30, and 40% CP), altered by changing the ratio of soybean meal to sorghum grain in supplements. Supplements wer e fed at 13.9 and 14.1 kg of DM/wk for Exp. 1 and 2, respectively. In Exp. 3, the second factor was supplement grain type (sorghum grain or corn) and supplements containing 21% CP were fed at 14.8 kg of DM/wk. In Exp. 1, eight ruminally fistulated steers (456 kg) consumed wheat s traw ad libitum. Pregnant beef cows grazing dormant tallgrass prairie were used in Exp. 2 (475 kg; n = 128) and 3 (504 kg; n = 120). In Exp. 1, reducing supplementation frequency decreased (P <.01) straw intake but increased (P less than or equal to.03) DM and NDF digestion. As C P concentration in supplements increased, straw DMI (P =.06) increased quadratically, whereas DM and NDF digestion increased linearly (P <.0 1). In Exp. 2, increasing CP concentration in supplements enhanced cow s' ability to maintain BW and condition up to calving, with decreasing magnitude of difference between treatments at higher CP concentration s (P < .01). Increasing CP in supplements fed to the dams linearly (P =.05) increased calf weaning weight in Exp. 2. In Exp. 2 and 3, reduci ng supplementation frequency increased (P less than or equal to.02) wi nter weight loss through calving. Grain type did not significantly aff ect most performance variables. In summary, response to supplementatio n frequency was not dependent on supplement CP concentration or grain type. Daily supplementation maximized forage intake and cow performanc e, although the magnitude of performance differences was not large.