Effects of feeding green chopped winter forages on digestibility, ruminal fermentation and blood parameters in beef steers

Abstract Text: An experiment was conducted in the winter over 2 consecutive yr to evaluate the effects of feeding green chopped winter forages on digestibility and ruminal fermentation parameters in beef steers.  Each yr, 9 ruminally cannulated Angus crossbred steers (yr 1: 359 ± 79 kg; yr 2: 481 ± 105 kg) received fresh chopped forage ad libitum, from pastures planted with one of the following mixtures: 1) FL401 cereal rye (Secale cereale L.)/Prine annual ryegrass (Lolium multiflorum Lam.) (RYE); 2) Horizon 201 oats (Avena sativa L.)/Prine annual ryegrass (OAT); 3) Trical 342 triticale (X Triticosecale spp.)/Prine annual ryegrass (TRIT).  Intake was measured throughout the study using GrowSafe, and any unconsumed forage was discarded prior to the next d feeding.  After a 14 d adaptation period, feed and fecal samples were collected twice daily for 4 d, to determine apparent total tract nutrient digestibility using indigestible NDF as a marker.  On d 19, blood and ruminal fluid samples were collected every 3 h during a 24 h period, to analyze blood urea nitrogen (BUN) and glucose in the plasma, as well as NH₃-N, pH, and VFA concentrations in ruminal fluid. Data were analyzed as a generalized randomized block design with repeated measures, using the Mixed Procedure of SAS, with treatment as a fixed effect and animal and yr as random effects. Treatments did not affect (P > 0.05) intake of DM, OM, CP, NDF, or ADF; however, apparent total tract digestibility of DM, OM, CP, NDF, and ADF was greater (P < 0.05) for OAT and TRIT, when compared with RYE. Steers fed OAT had greater concentrations of plasma glucose (P < 0.05) compared with TRIT and RYE.  An effect of sampling time (P < 0.01) was observed for ruminal pH; however no treatment or treatment × sampling time interactions were observed (P > 0.05).  Steers fed RYE had greater (P < 0.05) concentrations of NH₃-N, BUN, and the least concentrations of total VFA (P < 0.05). Molar proportion of acetate, branched-chain VFA and acetate:propionate were greater (P < 0.05)  for RYE when compared with OAT and TRIT. In conclusion, OAT and TRIT resulted in greater digestibility of nutrients, and ruminal fermentation and blood parameters that are conducive to enhanced growth performance when compared with RYE.

Keywords: fermentation, ruminants, winter forage