Influence of forage NDF level, source and pelletizing on growth performance, dietary energetics, and characteristics of digestive function for feedlot cattle

Abstract

One hundred sixty Holstein steers (222±1kg) were used in a 264-d growing-finishing trial to evaluate the influence of forage aNDFom level (40 vs 80g/kg DM) and source [ground forage (alfalfa, sudangrass, and rice straw) or pelletized rice straw] on growth performance. Forage source did not influence (P>0.10) gain efficiency or dietary net energy (NE). Daily weight gain (ADG) and dry matter intake (DMI) were similar (P>0.10) for alfalfa, sudangrass and ground rice straw. Pelletizing rice straw depressed ADG (P<0.01) and DMI (P<0.01). Increasing forage aNDFom decreased gain efficiency (P=0.09), and dietary NE (P=0.04). Four Holstein steers (197kg) with ruminal and proximal duodenal cannulas were used in a 4×4 Latin square design to compare effects of alfalfa vs sudangrass hay at 40 vs 80g/kg of forage aNDFom on digestion. There were no treatment effects on ruminal aNDFom digestion (P>0.10). Ruminal OM digestion was not affected by forage aNDFom level (P=0.96); however, it was greater (P=0.04) for sudangrass vs alfalfa supplemented diets. Microbial efficiency was not affected by forage aNDFom level (P=0.53); however, it was greater (P=0.02) for alfalfa vs sudangrass supplemented diets. Forage source did not affect total tract aNDFom digestion (P=0.86). However, aNDFom digestion was greater (P=0.08) for 80 vs 40g/kg of forage aNDFom. There were interactions between forage aNDFom level and source on total tract OM digestion (P=0.03). With alfalfa, level of forage aNDFom did not affect OM digestion. With sudangrass, increasing forage aNDFom decreased (P<0.05) total tract OM digestion. There were interactions between forage aNDFom level and source on ruminal pH (P=0.05), and acetate:propionate ratio. With alfalfa, increasing forage aNDFom did not affect ruminal pH, but increased acetate:propionate molar ratio. With sudangrass, the increasing forage aNDFom increased ruminal pH, but did not affect VFA molar ratios. Four Holstein steers (189kg) were used in a 4×4 Latin square design to compare effects of ground vs pelletized rice straw at 40 vs 80g/kg of forage aNDFom on digestion. There were no treatment effects (P>0.10) on ruminal OM digestion or microbial efficiency. Ruminal aNDFom digestion was greater (P=0.05) for pelletized vs ground rice straw. There were no treatment effects (P>0.10) on total tract aNDFom digestion. Pelletizing did not affect (P=0.78) total tract OM digestion. Tract OM digestion was greater (P=0.03) for 40 vs 80g/kg of forage aNDFom. Level of forage aNDFom did not affect (P>0.10) ruminal pH or VFA molar proportions. Ruminal pH and acetate:propionate molar ratio were greater (P<0.10) for ground vs pelletized rice straw. Differences among forage sources are minimized when forages are compared at similar levels of forage aNDFom concentration. Compared to ground, pelleted rice straw in finishing diets may produce lower ruminal pH and growth-performance of cattle.