Influence of Protein or Grain Supplementation and Increasing Levels of Soybean Meal on Intake, Utilization and Passage Rate of Prairie Hay in Beef Steers and Heifers

Abstract

To determine the effect of supplementation programs on intake and digestibility of prairie hay (PH) harvested in early July from a native range meadow, 16 Hereford steers were used in four replications of a 4 × 4 latin square. Steers had ad libitum access to PH (4% crude protein, CP; 48% acid detergent fiber, ADF). Treatments were: control (C, a mineral-vitamin mix); a low level (LL) of protein supplement (.36 kg of 32% CP); a high level (HL, .67 kg of 34% CP); and a grain-based (GR) supplement (1.41 kg of 13% CP) fed daily. The HL provided twice the supplemental protein of LL, whereas LL and GR provided similar amounts of supplemental protein. Supplementation increased (P < .01) PH intake, digestibilities of DM, organic matter (OM), CP, ADF and cellulose (CSE) and luminal NH3 concentrations. Compared with LL, HL increased forage intake, digestibilities of DM, OM, CP and CSE, ruminal NH3 concentrations (P < .01) and ADF digestibility (P < .05). Forage intake, ruminal NH3 and digestibilities of DM, OM, CP and ADF were similar (P > .05) between LL and GR, but higher than C. Ruminal pH was not altered. In a second experiment using three simultaneous 5 × 5 latin squares, soybean meal (SBM) was fed at 0, 121, 241, 362 and 603 g DM/d to 15 Angus-Hereford heifers (219 kg) with ad libitum access to early-cut PH (5% CP; 48% ADF). Added SBM resulted in a quadratic increase in forage intake, CP digestibility, ruminal NH3 concentration (P < .01) and in OM digestibility (P < .05), whereas linear increases (P < .01) were noted in digestibilities of DM, ADF and CSE and in particulate passage rate of forage. Rate of particulate passage and intake were highly correlated (r = .98). Added SBM consistently increased observed diet digestibilities above calculated digestibilities.