In situ disappearance of neutral detergent insoluble nitrogen from alfalfa and eastern gamagrass at three maturities.

In situ digestion kinetics of neutral detergent insoluble nitrogen (NDIN) from alfalfa (Medicago sativa L.) harvested at one-tenth bloom and eastern gamagrass (Tripsacum dactyloides L.) harvested at the boot (GGB), anthesis (GGA), and physiological maturity (GGM) stages of growth were determined with nonlinear regression techniques. Whole-plant tissue and associated leaf and stem fractions were incubated in the ventral rumen simultaneously. On a wholeplant basis, potential extents of degradation were particularly high (> or =904 g/kg NDIN) for GGB and GGA, relative to those of GGM and alfalfa (772 and 658 g/kg NDIN, respectively). For all plant parts, degradation rates of NDIN were faster (P<.05) for alfalfa than for all gamagrass forages. Degradation rate of NDIN did not differ (P>.05) across maturities for any gamagrass tissue type. These results indicate 1) that phenological development and lignification do not limit the rate of NDIN degradation in gamagrass forages but do markedly limit the potential extent of NDIN availability and 2) that most of the NDIN in these forages is potentially available in the rumen and can contribute to the ruminal N supply. Our secondary objective was to compare estimates of N escaping ruminal degradation that were determined on the basis of NDIN degradation kinetics (NDIN method) with those determined traditionally, on the basis of total residual N. The NDIN method mathematically eliminates all neutral detergent soluble N from consideration as part of the pool of dietary N potentially escaping the rumen intact. Estimates of rumen escape nitrogen determined on the basis of degradation rates of NDIN were consistently less than corresponding estimates that were determined on the basis of total residual N. When ruminal escape N that was determined with the NDIN method was regressed on corresponding estimates with the total residual N method, the slopes of the regression lines were .53 and .66 for assumed passage rates of .02 and .06 h(-1), respectively. For the forages evaluated in this study, these results indicate that neutral detergent soluble N may make important contributions to the pool of N escaping ruminal degradation.

Degradability of forage proteins by in situ and in vitro enzymatic methods.

The overall objective of these two studies was to evaluate the efficacy of using the proteolytic enzyme from Streptomyces griseus to estimate concentrations of ruminally degradable protein (RDP) in a wide array of forages. In the first study, alfalfa and prairie hays that previously had been evaluated in vivo for RDP were incubated in a replicated 3 x 3 factorial combination of enzyme concentrations (6.6, 0.66, and 0.066 activity units/ml of incubation medium) and incubation times (2, 4, and 48 h). Two treatment combinations (6.6 activity units for 4 h and 0.066 activity units for 48 h) yielded respective RDP estimates for alfalfa and prairie hay that were close to the known in vivo values. In the second study, 20 diverse forages were evaluated for RDP by using the in situ technique. These forages also were evaluated for RDP with the two enzyme concentrations identified in the first study, but incubation times were expanded to include 1, 2, 3, 4, and 5 h at the high concentration and 24, 30, 36, 42, 48, and 54 h at the low concentration. At the high enzyme concentration, r2 statistics from linear regressions of enzymatic estimates of RDP on corresponding estimates obtained by the in situ procedure were high (r2 > or = 0.898) at all incubation times; in addition, slopes (range = 0.88 to 1.00) and intercepts (range = -9.4 to 3.5%) approached unity and 0, respectively. At the lower enzyme concentration, r2 statistics were still good (> 0.81), but slopes (0.59 to 0.67) and intercepts (18.5 to 21.9%) for all incubation times did not meet the respective goals of unity and 0.

In situ dry matter, nitrogen, and fiber degradation of alfalfa, red clover, and eastern gamagrass at four maturities.

This study compared in situ degradation characteristics of dry matter, N, and neutral detergent fiber (NDF) for alfalfa and red clover with those for eastern gamagrass, a perennial, warm season grass that is native to the Flint Hills of Kansas. Gamagrass had a high proportion of leaf tissue (> 69%) at boot and anthesis stages, at physiological maturity, and after 56 d of regrowth following clipping at boot stage. Gamagrass also had high N concentrations at boot and anthesis stages (2.82 and 2.16%, respectively). Whole-plant gamagrass tissue contained a large proportion of N that was insoluble in neutral detergent (> 51%); however, this was a characteristic only of leaf tissue and was observed on a whole-plant basis because of the large proportion of leaf tissue at all plant maturities. Degradation characteristics of dry matter and NDF generally indicated that stem and cell-wall components from gamagrass at boot and anthesis stages had large maximum extents of degradation. Nitrogen degradation rates (0.047 to 0.059/h) were slower for whole-plant gamagrass than for alfalfa (0.213/h). The most distinguishing characteristic of these findings was not that N from gamagrass degraded more slowly in the rumen than did N from alfalfa or red clover, but that this trait was coupled with N concentrations at harvestable growth stages (boot or anthesis stages) that were similar to legumes.

Protein degradation in response to spontaneous heating in alfalfa hay by in situ and ficin methods.

Alfalfa forage, field-wilted to 29.9 or 19.7% moisture and packaged in five baling treatments (prestorage control; conventional bales; and laboratory bales made at 1.0, 1.5, and 2.0 times the density of conventional bales), was evaluated for protein degradation characteristics by in situ and ficin assays. Relationships between degradation rates and accumulated heating degree days suggested that these degradation rates are controlled by two conditions. Degradation rates increased concurrently with conservation and minimal heating, primarily because of a large redistribution of highly degradable N that was soluble in prestorage controls, but not in conserved hays. For both methods, this effect appeared to be maximized between 100 and 125 heating degree days. With respect to the in situ method, these effects appeared to be less pronounced, and degradabilities were not affected. After bales accumulated about 125 heating degree days, degradation rates decreased predictably in response to heating by both methods, as did N degradabilities calculated from in situ data. Increases in degradation rates concurrent with conservation and minimal heating appear to be especially important considerations when results of the ficin assay are being interpreted.

Evaluation of the potential of supplements to substitute for low-quality, tallgrass-prairie forage.

Thirteen ruminally fistulated steers (260 +/- 15 kg) were used in an incomplete Latin square with 13 treatments and four periods to evaluate the potential for different supplements to substitute for intake of low-quality, tallgrass-prairie forage. Steers were given ad libitum access to forage and received either no supplement (control = CTL) or one of four supplements, each fed at three different levels of intake. Supplements included 1) moderate CP (17.5%) concentrate (MCP-CON), 2) high CP (32.7%) concentrate (HCP-CON), 3) long-stem alfalfa hay (LSAH; 17.2% CP), and 4) alfalfa pellets (AP; 16.3% CP). Concentrates were mixtures of sorghum grain and soybean meal. Supplements were fed to supply .05, .10, and .15% BW of CP/d. Forage intake and digestible DMI were increased (P < .01) for supplemented steers compared with CTL (22 and 96%, respectively). Steers receiving increasing MCP-CON exhibited a quadratic (P = .03) forage intake response. Offering MCP-CON higher than .10% BW of CP/d (approximately .59% BW of DM) resulted in a substitution rate of -.56 g of forage/g of supplement. Although effects were not significant for steers receiving LSAH, the decline in forage intake at the high level of supplementation (-.48 g of forage/g of supplement) was similar in magnitude to that for MCP-CON. Forage intake increased linearly (P < .01) across supplementation levels for HCP-CON and AP supplements. Passage rates were faster (P < .01) for supplemented steers. However, passage rates for HCP-CON and AP groups increased linearly (P < .01) with increasing supplement, whereas they declined at the highest supplementation rate for MCP-CON and LSAH (quadratic, P < or = .05). Most fermentation variables displayed positive responses to supplementation per se and to increasing amount of supplements offered. In conclusion, although supplementation effectively enhances the use of low-quality forage, supplement type may affect the likelihood of observing substitution effects.

In situ digestion kinetics and ruminal turnover rates of normal and brown midrib mutant sorghum x sudangrass hays fed to nonlactating Holstein cows.

Four nonlactating Holstein cows were fed all-forage diets, consisting of two brown midrib mutant sorghum x sudangrass hybrids (Redlan x Greenleaf and Redlan x Piper) and their normal counterparts, to assess the effects of the brown midrib mutation on the rate and extent of in situ cell wall digestion and on ruminal liquid and particulate turnover rates. The four diets were preserved as hay and coarsely chopped prior to feeding in a 4 x 4 Latin square design. Brown midrib genotypes had lower NDF, acid detergent lignin, and hemicellulose concentrations than did normal genotypes. There was no significant difference between brown midrib and normal diets in the rate of in situ cell wall digestion or in digestion lag time. However, brown midrib diets had greater extent of digestion and greater apparent digestibility than normal diets. There was no difference between genotypes in ruminal liquid or particulate turnover rates. In this experiment, lignin concentration had no effect on the rate of in situ digestion or on the rate of ruminal digesta flow.