|Defoor, P - WEST TEXAS A&M UNIVERSITY|
|Gaylean, M - TEXAS TECH UNIVERSITY|
|Jones, O - TEXAS AGRIC EXT SERVICE|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 18, 2000
Publication Date: N/A
Interpretive Summary: In many years, because of drought or excess rain, the growing season for grain sorghum may be shortened. Producers may attempt to grow hybrids that require a shorter growing season in order to produce a crop that year. In addition, grain sorghum may be planted in narrow (38 cm) rows rather than normal (76 cm) rows because sorghum in narrow rows will mature faster and produce yields greater than or similar to sorghum in normal rows. Sorghum grown in narrow rows has a tendency to lodge and may have smaller seed size which can affect the nutritive value of the grain. Early harvesting of narrow row sorghum could potentially decrease lodging problems as well as increase the nutritive value of the grain sorghum. In the present experiment, five grain sorghum hybrids were grown in narrow and normal rows and were harvested when the grain contained approximately 35% moisture (high-moisture harvested) or at maturity (approximately 12% moisture). High moisture milo was ensiled in plastic bags. Mature grain was either steam-flaked or dry rolled. Laboratory tests were conducted to determine the effects of planting density and processing method on the nutrient composition and starch availability of the grains. Sorghum grown in narrow rows had less starch but more crude protein than sorghum grown in normal rows. The starch in the narrow-row sorghum was more digestible than the normal-row sorghum. Steam flaked sorghum had less protein but greater starch availability than high-moisture and dry rolled sorghums. These studies demonstrated that agronomic practices could affect the nutritive value of grain sorghum. Thus, diet formulations may need to be adjusted when cattle feeders are using sorghum grown in narrow rows.
Technical Abstract: Grain sorghum grown in 38- and 76-cm rows (High-Density (HD) and Normal-Density (ND), respectively) was steam-flaked (SF), high-moisture (HM) harvested followed by rolling and ensiling, or dry-rolled (DR). These grains were evaluated in a laboratory trial to determine the effects of grain sorghum planting density and subsequent processing on chemical composition, enzymatic starch availability, crude protein (CP) insolubility, and in vitro dry matter digestibility (IVDMD) in a reduced-strength buffer in vitro system. In addition, the relationship between enzymatic starch availability and in vitro pH change in the reduced strength buffer in vitro system was evaluated. High-density planting increased (P<.10) OM and starch concentration and decreased CP concentration, but did not affect (P>.10) P concentration, enzymatic starch availability or CP solubility. Relative to ND, HD planting resulted in lower (P>.10) in vitro ruminal culture pH at 6 and 12 h, and lower (P<.10) IVDMD at 6, 12, 18, and 24 h of digestion. However, HD planting seemed to increase (P<.10) the IVDMD of SF sorghum. Steam flaking decreased (P<.10) CP concentration and solubility, increased (P<.10) OM concentration, and tended (P<.13) to increase starch concentration. High-moisture ensiling increased (P<.10) the solubility of CP, but did not otherwise seem to alter the chemical composition of grain sorghum relative to dry rolling. Starch was more available (P<.10), and dry matter (DM) was digested more rapidly and extensively (P<.10) in vitro in SF sorghum followed by HM sorghum.