Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/26/2000
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 grown in narrow rows will mature faster and produce yields greater than or similar to sorghum grown in normal rows. Sorghum grown in narrow rows may have smaller seed size which can affect the nutritive value of the grain when it is processed by methods such as steam flaking: the most common method used in beef cattle feedyards. Sorghum grown in narrow rows also has a greater tendency to lodge in the field. 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, grain sorghum was grown in narrow and normal rows and was 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. The grains were fed to sheep in either 60% or 90% concentrated diets and nutrient digestion and retention were determined. The nitrogen and phosphorus of sorghum planted in narrow rows was more digestible than from sorghum planted in normal rows. 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 two 5 x 5 Latin square digestion trials to determine the effects of planting density and processing method on in vivo utilization by ruminants. Treatment diets contained either SFHD, SFND, HMND, or DRND grain sorghum fed in 90 or 60% concentrate diets to lambs in Trials A and B, respectively. Nitrogen retention data from the 60% concentrate trial suggested that relative to ND, HD planting resulted in greater retention of N (P < .10). Data from both the 90 and 60% concentrate digestion trials indicated that HD planting may increase (P = .12 and .11, respectively) the total tract digestibility of P. Retention of P was greater for the HD than for the ND sorghum in the 60% concentrate trial, and the HD sorghum tended (P = .22) to be associated with a higher overall P retention than the ND sorghum (22.6 vs 17.5%, respectively). Relative to HM ensiling, steam flaking decreased (P < .10) the total tract digestibility of N in the 90 and 60% concentrate trials and P in the 90% concentrate trial; however, the two processing methods resulted in similar (P > .10) N and P retention as a percentage of intake. These data indicate that HD planting and processing can alter the nutritive value of grain sorghum for ruminants.