Submitted to: Crop Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/1/2011
Publication Date: 7/6/2011
Citation: Burns, J.C. 2011. Intake and Digestibility Among Caucasian Bluestem, Big Bluestem, and Switchgrass Compared with Bermudagrass. Crop Science. 51:2262-2275. Interpretive Summary: Four experiments were conducted to compare dry matter intake (DMI), dry matter digestion (DMD), and masticate characteristics among five perennial, warm-season forage grasses. In general, initial and regrowth Caucasian bluestem (CBS) hays were readily consumed and regrowth CBS was greater in nutritive value, and consequently DMI and DMD, at similar maturity. The greater quality of regrowth hay, although produced under elevated temperatures and potential water stress and generally associated with reduced nutritive value, was apparently offset by adequate moisture, shorter regrowth interval, and shifts in leaf to stem ratio at comparable maturity as initial growth. Initial growth of CBS was superior to switchgrass (SG) in digestible DMI when harvested at similar physiological maturity. Further, regrowth CBS was also similar to regrowth T44 bermudagrass in digestible DMI but initial growth of CBS was less. It is worth noting that SG, regardless of growth, retained moisture in the field longer compared with either T44 or CBS. Despite some differences in nutritive value and masticate characteristics the regrowth hays of both CBS and BBS were similar in intake and digestion. Consequently, they would both be expected to readily substitute one for the other. It is worthy to note that big bluestem (BBS) cured rapidly in the field and reached moisture status for baling prior to CBS. This attribute warrants further attention, especially in summer environments that have frequent, rapidly forming, rainfall events. Although differences existed in nutritive value and masticate characteristics among the initial and regrowth CBS and BBS hays, animals consumed them similarly, whereas DMD was less consistent. On the other hand, digestible DMI of the four hays were sufficiently similar that comparable animal performance would be expected from each. All forage species were readily cut and baled as hay with conventional equipment and were easily field cured. Steers consumed all hays well and, with the exception of SG and regrowth BBS, the apparent digestibilities exceeded 610 g kg-1. Dry matter intakes ranged from 2.0 to 2.7 kg 100-1 kg BW. Except for SG, digestible DMI of hays ranged from 1.2 to 1.7 kg 100-1 kg BW. Although cut at similar growth stages within an experiment, the two taller growing species (i.e. SG and BBS), compared with the two shorter growing species (i.e. CBS and bermudagrasses) had considerable stem development which contributed to their reduced DMI and DMD. In general, all five warm-season grasses evaluated can produce hay of adequate quality, which can be increased or decreased based on maturity at time of harvest, for advantageous use in ruminant production systems.
Technical Abstract: Warm-season perennial grasses, mainly bermudagrass, have been a major source of hay for ruminant systems across the upper southern USA. This study compares the quality of Caucasian bluestem [Bothriochloa caucasia (Trin.) C.E. Hubbard ‘Caucasian’] (CBS) with ‘Kanlow’ switchgrass (Panicum virgatum L.) (SG), and big bluestem (Andropogon gerardii Vitman) (BBS), relative to ‘Coastal’ and ‘Tifton’ bermudagrasses [Cynodon dactylon (L.) Pers.], as forages for the upper south. Four intake and digestion experiments, with associated diet characteristics, were conducted using steers. In experiment (Exp.) 1, CBS regrowth (45 d) compared with initial growth, had greater (P = 0.01) daily dry matter (DM) intake (DMI) [2.33 vs. 1.91 kg 100-1 kg body weight (BW)] and apparent DM digestibility (DMD) (664 vs. 617 g kg-1). Initial growth bermudagrass had greater (P < 0.01) DMI than CBS (2.61 vs. 1.91 kg 100 kg-1 BW) and similar DMD (mean = 619 g kg-1). In Exp. 2, initial and regrowth (45 d) CBS, compared with SG, had greater (P < 0.01) DMI (2.06 vs. 1.23 kg 100-1 kg BW). In Exp. 3 regrowth CBS and BBS had similar DMI (mean = 1.83 kg 100-1 kg BW) and DMD (mean = 637 g kg-1). In Exp. 4 initial and regrowth (53 d) CBS and regrowth (57 d) BBS had similar DMI (mean = 2.29 kg 100-1 kg BW) but CBS had greater (P = 0.01) DMD (602 vs. 566 g kg-1). The DMI and DMD of all hays in all experiments (n = 15) were correlated (r = 0.66, P < 0.01). In general all hays can contribute to ruminant production systems.