In Vitro True Digestibility Research Articles

Yield, Digestibility, and Nutritive Value of Crabgrass as Impacted by Nitrogen Fertilization Rate and Source

Crabgrass (Digitaria spp.), a summer annual grass capable of self reseeding, could provide high quality grazing, but little is known about its management in the mid‐Atlantic region. This study evaluated the effects of N fertilizer rates and sources on crabgrass yield and nutritive value. Plots were established in late spring of 2001–2003 near Blackstone, VA. The experimental design was a randomized complete block with a factorial treatment arrangement and four replications. Nitrogen rates ranging from 0 to 336 kg ha−1 were applied in 56‐kg intervals at seeding as ammonium nitrate (NH4NO3) or broiler litter. Plots were harvested twice in 2001 and three times in 2002 and 2003. Yield increased with N rate for all harvests. Over years and N sources, seasonal yield ranged from 4.2 to 9.8 Mg ha−1. Maximum yield occurred at 300 kg N ha−1. Nitrogen source had little effect on yield but dramatically impacted forage nitrate levels. Over years and N sources mean in vitro true digestibility (IVTD) for first, second, and final harvests were 880, 871, and 786 g kg−1. In 2001 and 2003, first harvest IVTD was negatively correlated with N rate, but positively related at second harvest. Nitrogen source had little effect on IVTD. Over years, N rates, and N sources, CP concentrations at first, second, and final harvests were 105, 105, and 76 g kg−1. These data indicate that crabgrass is a productive and nutritious forage, and that readily available organic N sources such as broiler litter could be effectively utilized for its production.

Leaf and Stem Characteristics of Timothy Plants Divergently Selected for the Ratio of Lignin to Cellulose

Improved dry matter (DM) digestibility of herbage can be due to changes in fiber composition of leaves and/or stems, and/or to changes in the proportion of leaves and stems in the herbage. Previously, we reported that divergent selection for the ratio of acid detergent lignin (ADL) to cellulose (ADL/CEL) led to differences in timothy (Phleum pratense L.) DM digestibility. Here, we examined plant morphology (leaf‐to‐stem ratio, plant height and area, and stem diameter), leaf and stem fiber composition, and leaf and stem digestibility in timothy genotypes selected for high or low values of ADL/CEL and in divergent progeny populations derived from these selections. Parental genotypes and their progeny populations were field grown for 2 yr, and measurements were taken at the first harvest of each year. Selection for low values of ADL/CEL reduced ADL and neutral detergent fiber (NDF) concentrations in stems and increased the in vitro true digestibility (IVTD) of stems but had no consistent direct effects on plant morphology or leaf characteristics. Averaged over 2 yr, stems of the low‐ADL/CEL group of genotypes had lower ADL and NDF concentrations (by 3.4 and 12 g kg−1 DM, respectively) and a higher IVTD value (by 22 g kg−1 DM) than those of the high ADL/CEL group of genotypes. In addition, stems of the low‐ADL/CEL progeny population had lower ADL and NDF concentrations (by 4.2 and 26 g kg−1 DM, respectively) and a higher IVTD value (by 22 g kg−1 DM) than those of the high ADL/CEL progeny population. Thus, the observed changes in overall herbage DM digestibility due to selection for this ratio can be attributed mainly to modification of stem digestibility.

Illinois Bundleflower Forage Potential in the Upper Midwestern USA: II. Forage Quality

Illinois bundleflower [Desmanthus illinoensis (Mich.) MacMill] is a warm‐season perennial legume native to the central USA. Little is known about its forage quality in the upper midwestern USA. Two experiments were established at four Minnesota locations in 2000 to evaluate the effects of N fertilization, maturity at harvest, and residual height of cutting on the acid detergent fiber (ADF), neutral detergent fiber (NDF), crude protein (CP), in vitro true digestibility (IVTD), in vitro dry matter digestibility (IVDMD), and leaf proportion of three Illinois bundleflower (IBF) ecotypes. Whole‐herbage forage quality was greatest (P < 0.05) at early flower in mid‐July with average ADF, NDF, and CP concentrations of 315, 352, and 180 g kg−1, respectively. Fiber values increased to 412 and 479 g kg−1, respectively, while CP decreased to 129 g kg−1 at late pod in mid‐August. Leaf proportion decreased (P < 0.05) from 618 g kg−1 at early flower to 335 g kg−1 at late pod while leaf CP decreased (P < 0.05) from 216 to 147 g kg−1. Whole‐herbage IVDMD and IVTD concentrations decreased (P < 0.05) from 470 and 648 g kg−1 at early flower to 390 and 560 g kg−1 at late pod, respectively. Increasing residual cutting height from 15 to 35 cm decreased (P < 0.05) ADF and NDF concentrations by an average of 50 g kg−1 and increased (P < 0.05) IVTD, IVDMD, and CP concentrations by 43, 39, and 20 g kg−1, respectively. Illinois bundleflower can provide good quality summer forage in the upper midwestern USA, but more research is needed to ascertain the implications of its low IVDMD on animal performance.

Responses to Divergent Phenotypic Selection for Fiber Traits in Timothy

Selection based on fiber traits may make it possible to improve forage digestibility while maintaining plant biomass. Our objectives were to evaluate the effects of divergent phenotypic selection for fiber traits on timothy (Phleum pratense L.) digestibility, plant biomass, fiber component concentrations and their ratios, and to identify selection criteria that have effective and stable effects on timothy digestibility without affecting plant biomass. Fourteen populations derived by intercrossing plants selected for high or low values of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and cellulose (CEL) concentrations, and for ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) ratios were evaluated in a field experiment. Direct responses for the selected traits were significant for the NDF, CEL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) populations. Indirect responses for in vitro true digestibility (IVTD) and in vitro NDF digestibility (IVNDFD) were greatest for the ratios involving ADL. The ADL/CEL selection resulted in the most stable responses across years for IVTD and IVNDFD. Averaged over 2 yr, the IVTD and IVNDFD of the low ADL/CEL population were 27 g kg−1 DM and 33 g kg−1 NDF greater than those of the high ADL/CEL population. Furthermore, the low ADL/CEL population maintained its HEM and CEL concentrations and its plant biomass. Phenotypic selection based on ADL/CEL could be used to improve timothy DM digestibility without reducing plant biomass.

Effects of Swine Lagoon Effluent Relative to Commercial Fertilizer Applications on Warm‐Season Forage Nutritive Value

Two field experiments were conducted to evaluate the effects of comparable rates of swine lagoon effluent and commercial fertilizer at different harvest dates on dry matter yield and nutritive value of bermudagrass (Cynodon dactylon L.) grown on an acid Vaiden silty clay (very fine, montmorillonitic, thermic, Vertic Hapludalf) and johnsongrass (Sorghum halepense L.) grown on an alkaline Okolona silty clay (fine, montmorillonitic, therimic, Typic Chromudert). At each site, a randomized complete block design with a factorial arrangement of treatments replicated four times was used. Treatments were multiple effluent irrigations resulting in four N rates from 0 to 665 kg N ha−1 yr−1. In each block, commercial fertilizer (N, P, and K) treatments were applied to additional plots at rates equivalent to swine effluent rates. Total dry matter yield and crude protein (CP) for bermudagrass and johnsongrass reached a plateau with application of approximately 450 kg N ha−1 from either swine effluent or commercial fertilizer. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) peaked at the low fertilization rate and then declined with increasing effluent and commercial fertilizer rates. An inverse relationship was obtained for in vitro true digestibility (IVTD) in response to fertilization rate for both grasses. Forage dry matter, CP, NDF, and ADF levels peaked in the July harvest and then declined, but forage IVTD level declined in July harvest. Only in July 1996, forage NO3–N concentration was lower for swine effluent than commercial fertilizer. Swine effluent and commercial fertilizer had similar effects on forage dry matter yield and nutritive value.

Timing Corn Forage Harvest for Bunker Silos

Dairy producers with large operations have switched from upright to bunker silos so they begin corn (Zea mays L.) forage harvest at 300 g kg−1 instead of 350 g kg−1 dry matter (DM) content. Three hybrids were harvested at average DM contents of 295, 310, and 350 g kg−1 to compare DM yield and forage quality of corn forage typical of bunker and upright silos. Hybrid and DM content did not have interactions for DM yield and forage quality characteristics. The DM content at harvest did not affect DM yield (14.6, 15.0, and 15.1 Mg ha−1 at 295, 310, and 350 g kg−1, respectively). As DM content increased, neutral detergent fiber (NDF) declined (469, 447, and 417 g kg−1, respectively), but NDF digestibility (657, 632, and 631 g kg−1) and crude protein (78, 73, and 72 g kg−1) declined only from 295 to 310 g kg−1 As DM content increased, milk per megagram, a forage quality index, increased (1622, 1699, and 1764 kg Mg−1 respectively), but in vitro true digestibility (IVTD) increased (839, 835, and 847 g kg−1), only from 310 to 350 g kg−1 Calculated milk yields differed at DM contents of 295 (24380 kg ha−1) vs. 350 g kg−1 (26947 kg ha−1) but not at 310 g kg−1 (25727 kg ha−1). Results from this study indicate that dairy producers with bunker silos do not compromise DM and calculated milk yields, despite somewhat lower forage quality, if they begin harvest at 310 g kg−1 DM content.

Leaf and stem nutritive value of timothy genotypes under varying N fertilization

Populations and half-sib families of timothy (Phleum pratense L.), contrasting in forage N concentration, were studied in two experiments conducted in growth rooms with varying N applications. They differed in leaf and stem in vitro true digestibility (IVTD) of DM and in vitro cell wall digestibility (IVCWD), and in stem neutral detergent fiber (NDF) concentration; this confirms the presence of genetic variability for leaf and stem nutritive value in timothy under both limiting and non-limiting N conditions. Key words: Digestibility, grasses, Phleum pratense, neutral detergent fiber, acid detergent fiber

Selection for Silage Quality in the Wisconsin Quality Synthetic and Related Maize Populations

Maize (Zea mays L.) silage is a high‐quality forage for ruminants, but there have been few significant breeding efforts specifically dedicated to improving maize forage yield or quality by breeders in the USA. The objective of this study was to evaluate the forage yield and quality of the Wisconsin Quality Synthetic (WQS) and related populations developed by the University of Wisconsin Maize Breeding Program for agronomic and nutritional attributes. Three cycles of divergent S1 recurrent selection have been completed for stover fiber, silica, and lignin concentration for populations WFISIHI (Wisconsin‐fiber‐silica‐high) and WFISILO (Wisconsin‐fiber‐silica‐low). The third cycle (C3) of WFISILO was crossed to two high‐quality inbred lines, Mo17 and H99, to create WQS C0, which then underwent two cycles of S2–topcross selection for improved forage yield and quality. All cycles of selection for WFISIHI, WFISILO, and WQS were evaluated for forage yield and quality at two field locations in Wisconsin in 2000 and 2001. Results for WFISIHI and WFISILO demonstrated that S1 selection for stover composition altered both stover and whole‐plant composition in the anticipated directions. Selection for whole‐plant yield and composition of S2–topcrosses was also effective for WQS, especially when using selection indices incorporating whole‐plant yield, neutral detergent fiber (NDF), neutral detergent fiber digestibility (NDFD), crude protein (CP), and starch. WQS C2 whole‐plant and stover in vitro true digestibility (IVTD), whole‐plant and stover acid detergent lignin, and milk yield per megagram dry matter (DM) were similar to the brown‐midrib check hybrid, F657. WQS C2 whole‐plant and stover NDFD were lower than F657 but higher than other commercial check hybrids. In addition, WQS population testcrosses improved over cycles of selection for whole‐plant yield and most quality attributes. Our results indicate that it is feasible to develop silage maize germplasm with both high whole‐plant yield and excellent nutritional quality.

Characteristics of Timothy Genotypes Divergently Selected for Fiber Traits

Selection for reduced fiber concentration in forage crops is considered to be an effective approach to improve digestibility but often results in reduced dry matter (DM) yield. The objective of this study was to characterize timothy (Phleum pratense L.) genotypes divergently selected for fiber component concentrations and their ratios, and to identify selection criteria that could have a meaningful effect on timothy digestibility without adversely affecting DM yield. Divergent phenotypic selection was applied for neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemicellulose (HEM), and cellulose (CEL) as determined by the detergent fiber system of forage analysis and for ratios of ADL/HEM, ADL/CEL, ADL/(HEM+CEL), and HEM/CEL among 78 high yielding plants selected from among 2000 spaced plants from four populations. For each criterion, the two plants with the highest and the two plants with the lowest values within each population were selected. These plants were vegetatively propagated and composition of spring growth was evaluated in a 2-yr field experiment. The divergent NDF, ADF, ADL, CEL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) groups of genotypes were significantly different for their respective trait. The ADL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) groups were the most stable across years for in vitro true digestibility (IVTD), with the low groups having values of IVTD between 10 and 34 g kg−1 DM above those of the corresponding high groups. The DM yield of the low-ADL/(HEM+CEL) and-ADL/CEL groups were also greater than that of their corresponding high groups by more than 13%. Therefore, ADL/(HEM+CEL) and ADL/CEL seem to be promising selection criteria to increase digestibility while maintaining or increasing DM yield.

Characteristics of Timothy Genotypes Divergently Selected for Fiber Traits

Selection for reduced fiber concentration in forage crops is considered to be an effective approach to improve digestibility but often results in reduced dry matter (DM) yield. The objective of this study was to characterize timothy (Phleum pratense L.) genotypes divergently selected for fiber component concentrations and their ratios, and to identify selection criteria that could have a meaningful effect on timothy digestibility without adversely affecting DM yield. Divergent phenotypic selection was applied for neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), hemicellulose (HEM), and cellulose (CEL) as determined by the detergent fiber system of forage analysis and for ratios of ADL/HEM, ADL/CEL, ADL/(HEM+CEL), and HEM/CEL among 78 high yielding plants selected from among 2000 spaced plants from four populations. For each criterion, the two plants with the highest and the two plants with the lowest values within each population were selected. These plants were vegetatively propagated and composition of spring growth was evaluated in a 2‐yr field experiment. The divergent NDF, ADF, ADL, CEL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) groups of genotypes were significantly different for their respective trait. The ADL, ADL/HEM, ADL/CEL, and ADL/(HEM+CEL) groups were the most stable across years for in vitro true digestibility (IVTD), with the low groups having values of IVTD between 10 and 34 g kg−1 DM above those of the corresponding high groups. The DM yield of the low‐ADL/(HEM+CEL) and‐ADL/CEL groups were also greater than that of their corresponding high groups by more than 13%. Therefore, ADL/(HEM+CEL) and ADL/CEL seem to be promising selection criteria to increase digestibility while maintaining or increasing DM yield.

Nutritive Value of Chicory and English Plantain Forage

Forage production in midsummer is a challenge for graziers in the northeastern USA. Domesticated cultivars of chicory (Cichorium intybus L.) and English plantain (Plantago lanceolata L.) are available in the USA as perennial herbs for pastures. These species have been touted as having good summer production and relatively high nutritive value. We conducted two field‐plot experiments at Rock Springs, PA, during 1997 to 2001 to evaluate the nutritive value of chicory and plantain under clipping. ‘Grasslands Puna’, ‘Lacerta’, and ‘Forage Feast’ chicory and ‘Ceres Tonic’ and ‘Grasslands Lancelot’ grazing plantain were sown in field plots in May 1997 and 1999 and harvested multiple times in 1998 (Exp. 1) and 2000 (Exp. 2). Herbage from three harvests in 1998 and two harvests in 2000 was analyzed for in vitro true digestibility (IVTD); neutral detergent fiber (NDF); and the minerals P, K, Ca, Mg, Mn, Cu, B, and Zn. Averaged for cultivars, chicory had 11% higher (P < 0.05) IVTD and 6 to 20% lower (P < 0.05) NDF than plantain. Concentrations of all minerals, except for Ca, were 17 to 48% higher (P < 0.05) in chicory than in plantain. There were few meaningful differences in nutritive value among cultivars within chicory or plantain. Chicory and plantain are of relatively high nutritive value and could enhance the nutritional profile of mixed species pastures. The nutritive value benefits, however, must be balanced against the lack of persistence of chicory and plantain.

Forage Nutritional Characteristics of Orchardgrass and Perennial Ryegrass at Five Irrigation Levels

As water resources become limiting, the need to produce stable amounts of highly nutritional forage increases. An understanding of how levels of irrigation affect crude protein (CP), digestible neutral detergent fiber (dNDF), in vitro true digestibility (IVTD), and neutral detergent fiber (NDF) is critical in pasture forage management. Cultivars of orchardgrass (Dactylis glomerata L.) and perennial ryegrass (Lolium perenne L.) were established under a line‐source irrigation system to evaluate the effect of five water levels (WLs) and three harvest dates on concentrations of CP, dNDF, IVTD, and NDF. Perennial ryegrass forage had higher CP, dNDF, and IVTD and lower NDF concentrations than orchardgrass at all harvest dates and within WLs. The most notable trend in nutritional value across WLs was the near linear increase in CP ranging from 175 g kg−1 at the wettest WL to 217 g kg−1 at the driest WL. Digestible NDF ranged from 709 to 757 g kg−1 at corresponding WLs. These trends were particularly evident later in the growing season. Orchardgrass maturity (early vs. late) had little effect on forage nutritional characteristics across WLs. Combined over WLs, tetraploid perennial ryegrass cultivars averaged higher concentrations of CP, IVTD, and dNDF and lower NDF values compared with diploid cultivars. In general, as water stress increased, forage nutritional value (i.e., CP and dNDF) increased.

Forage Nutritional Characteristics of Orchardgrass and Perennial Ryegrass at Five Irrigation Levels

As water resources become limiting, the need to produce stable amounts of highly nutritional forage increases. An understanding of how levels of irrigation affect crude protein (CP), digestible neutral detergent fiber (dNDF), in vitro true digestibility (IVTD), and neutral detergent fiber (NDF) is critical in pasture forage management. Cultivars of orchardgrass (Dactylis glomerata L.) and perennial ryegrass (Lolium perenne L.) were established under a line-source irrigation system to evaluate the effect of five water levels (WLs) and three harvest dates on concentrations of CP, dNDF, IVTD, and NDF. Perennial ryegrass forage had higher CP, dNDF, and IVTD and lower NDF concentrations than orchardgrass at all harvest dates and within WLs. The most notable trend in nutritional value across WLs was the near linear increase in CP ranging from 175 g kg−1 at the wettest WL to 217 g kg−1 at the driest WL. Digestible NDF ranged from 709 to 757 g kg−1 at corresponding WLs. These trends were particularly evident later in the growing season. Orchardgrass maturity (early vs. late) had little effect on forage nutritional characteristics across WLs. Combined over WLs, tetraploid perennial ryegrass cultivars averaged higher concentrations of CP, IVTD, and dNDF and lower NDF values compared with diploid cultivars. In general, as water stress increased, forage nutritional value (i.e., CP and dNDF) increased.

Forage Quality of Tall Fescue across an Irrigation Gradient

Water available for irrigating pastures in the western USA is often limited and varies widely across sites and seasons. Objectives were to determine the trends in crude protein (CP), neutral detergent fiber (NDF), and in vitro true digestibility (IVTD) of 10 cultivars of tall fescue (Festuca arundinaceae Schreb.) at five levels of irrigation and three harvest dates (early, mid‐, and late season). A secondary objective was to evaluate the effect of the endophytic fungus [Neotyphodium coenophialum (Morgan‐Jones & Gams) Glenn, Bacon & Hanlin] on these trends. Cultivars differed significantly for CP, NDF, and IVTD, and differences were generally consistent across water levels (WLs). Concentration of CP increased in a near linear manner (154–189 g kg−1) from the highest to lowest WL; however, total protein yield decreased from 611 to 447 kg ha−1 with less water, closely following the trend in forage yield. Forage quality at the late‐season harvest, as indicated by lower NDF and higher IVTD values, was significantly higher at the lowest compared with the highest WL. Also, NDF was significantly lower and IVTD significantly higher at the late‐season harvest at all WL. Presence or absence of the endophyte was not associated with CP; however, there was a tendency for the endophyte‐free cultivar to have lower NDF and higher IVTD than its endophyte‐infected counterpart at the higher WL. The magnitude of quality differences among the 10 cultivars indicates that forage quality should be a major consideration in the choice of cultivars for pastures of the Intermountain region.

Cultivar and Environment Effects on Annual Ryegrass Forage Yield, Yield Distribution, and Nutritive Value

ABSTRACTDifferences among annual ryegrass (Lolium multiflorum Lam.) cultivars for weight gain of grazing steers have been reported, even though plot experiments suggest that forage dry matter yield among cultivars should not be a limiting factor. Likewise, forage nutritive value differences among cultivars have not been assessed. The objectives of this research were to evaluate differences in cumulative forage yield, yield distribution, and nutritive value among ‘Gulf’, ‘Jackson’, ‘Marshall’, ‘Rio’, ‘Rustmaster’, and ‘Surrey’ annual ryegrass. Plots were harvested six times beginning in December at approximate 30‐d intervals during the 1997–1998 and 1998–1999 growing seasons. Nutritive value measurements included crude protein (CP), neutral detergent fiber (NDF), in vitro true digestibility (IVTD), and digestible NDF (DNDF). There were no differences among cultivars for cumulative forage yield (P = 0.99). However, for the January harvest, Surrey and Gulf averaged 1030 (±65) kg DM ha−1, whereas Marshall yielded only 672 (±79) kg DM ha−1 For the March harvest, yields of all varieties were similar and averaged 1350 (±95) kg DM ha−1 At the May harvest, Marshall and Jackson yielded 1232 (±123) kg DM ha−1, whereas Gulf yielded only 929 (±74) kg DM ha−1 Crude protein concentration differed significantly among harvests with a general decrease from 260 to 120 g CP kg−1 as the growing season progressed. Similar declines in nutritive value occurred for NDF, IVTD, and DNDF. Trends in yield distribution and forage quality may indicate a need for cultivar specific recommendations based on intended forage need and season of use.

Harvest Date and Hybrid Influence on Corn Forage Yield, Quality, and Preservation

The selection of corn (Zea mays L.) hybrids and the timing of harvest are important management considerations for dairy and livestock operations. Objectives of this study were to determine the effect of harvest date on yield and quality of corn hybrids and to describe the relationship between harvest date and the yield and quality of corn forage, silage, and stover. During 1998 and 1999, four hybrids were harvested at eight different harvest times between 521 and 1224 growing degree units (GDUs) after planting. Few hybrid or hybrid × harvest date effects were observed. As GDUs accumulated, dry matter yield increased from 8 to 25 Mg ha−1. Lowest concentrations of neutral detergent fiber (NDF) and acid detergent fiber (ADF) and highest concentrations of in vitro true digestibility (IVTD) occurred when forage was harvested between 700 and 650 g kg−1 moisture (1025 and 1186 GDUs after planting). Potential milk yield indices of milk Mg−1 corn forage (794 kg) and milk ha−1 corn forage (19 049 Mg) were reached when corn was harvested between 670 and 630 g kg−1 moisture. In general, silage had 15% lower concentrations of NDF, 8% lower IVTD, 48% lower cell wall digestibility, 7% lower crude protein, and 15% higher concentrations of ADF than unfermented fresh forage. Harvesting can be accomplished until 580 g kg−1 moisture while maintaining 95% of the maximum yield and milk ha−1

Harvest Date and Hybrid Influence on Corn Forage Yield, Quality, and Preservation

The selection of corn (Zea mays L.) hybrids and the timing of harvest are important management considerations for dairy and livestock operations. Objectives of this study were to determine the effect of harvest date on yield and quality of corn hybrids and to describe the relationship between harvest date and the yield and quality of corn forage, silage, and stover. During 1998 and 1999, four hybrids were harvested at eight different harvest times between 521 and 1224 growing degree units (GDUs) after planting. Few hybrid or hybrid × harvest date effects were observed. As GDUs accumulated, dry matter yield increased from 8 to 25 Mg ha−1. Lowest concentrations of neutral detergent fiber (NDF) and acid detergent fiber (ADF) and highest concentrations of in vitro true digestibility (IVTD) occurred when forage was harvested between 700 and 650 g kg−1 moisture (1025 and 1186 GDUs after planting). Potential milk yield indices of milk Mg−1 corn forage (794 kg) and milk ha−1 corn forage (19 049 Mg) were reached when corn was harvested between 670 and 630 g kg−1 moisture. In general, silage had 15% lower concentrations of NDF, 8% lower IVTD, 48% lower cell wall digestibility, 7% lower crude protein, and 15% higher concentrations of ADF than unfermented fresh forage. Harvesting can be accomplished until 580 g kg−1 moisture while maintaining 95% of the maximum yield and milk ha−1

In vitro rumen fermentation and gas production: influence of yellow grease, tallow, corn oil and their potassium soaps

The effect of addition of fat on in vitro gas production, volatile fatty acid (VFA) production, in vitro true digestibility (IVTD), and ammonia-N concentration was assessed by incubation of a simulated total mixed ration in buffered rumen fluid using an in vitro gas technique. Fat sources were corn oil (CO), tallow (TL), yellow grease (YG), and potassium soaps (K-soaps) of CO, YG, and TL. Addition of YG increased ( P<0.001) in vitro gas production while TL had no effect. Neither YG nor TL affected IVTD and total VFA production. Addition of either YG or TL decreased acetate production and increased propionate production. Addition of CO increased in vitro gas production, but had no effect on IVTD and total VFA production. However, CO decreased acetate and increased propionate production with a concomitant decrease in the acetate to propionate ratio. Addition of K-soaps of CO, TL and YG depressed in vitro gas production, IVTD, VFA and ammonia-N concentrations. K-soaps also caused a marked decrease in acetate and increase in propionate production. The absence of negative effects on rumen fermentation parameters in response to the inclusion of fat in the form of triglycerides to an in vitro system at up to 25% DM suggests that triglycerides have much less effect on rumen fermentation parameters than corresponding free fatty acids. In contrast, the K-soaps of each respective fat had detrimental effects on in vitro rumen fermentations.

Influence of Brown Midrib, Leafy, and Transgenic Hybrids on Corn Forage Production

Hybrid selection strongly influences corn (Zea mays L.) forage production. Limited forage production and quality information exists for leafy and transgenic hybrids [Bacillus thuringiensis (Bt) and herbicide resistant]. We compared dry matter (DM) yield, forage quality, and estimated milk yields of these and brown midrib hybrids with dual‐purpose hybrids for 3 yr at harvest densities of 66000 and 84000 plants ha−1. Transgenic hybrids had no effect on DM and milk yields, so we do not recommend Bt hybrids under conditions of low infestation of European corn borer (Ostrinia nubilalis Hubner). Leafy hybrids had similar DM and milk yields as hybrids of similar maturity. Brown midrib hybrids, which had DM yields that were about 20% less than those of hybrids of similar maturity, had 40 to 80 g kg−1 greater in vitro true digestibility (IVTD) and 70 to 200 g kg−1 greater neutral detergent fiber (NDF) digestibility. Brown midrib hybrids had the greatest or least milk yields among hybrids, depending on hybrid and year. Leafy and brown midrib hybrids mostly had low harvest index (HI) values, which had strong negative correlations with NDF in all years (−0.71, −0.44, and −0.90). Brown midrib hybrids had high NDF digestibility, which had strong positive correlations with IVTD (0.80, 0.88, and 0.86). Currently, we do not recommend brown midrib hybrids because of inconsistent milk yields and high seed costs. Development of brown midrib and leafy hybrids with greater HI values should result in excellent forage hybrids.

Nutritive Value Responses of Rhizoma Peanut to Nitrogen and Harvest Frequency

Management strategies to enhance or preserve nutritive value of rhizoma peanut (Arachis glabrata Benth.) would be beneficial because high plant growth rates and adverse weather at harvest often result in low nutritive value for both pastures and hay along the coastal plain of the lower Gulf Coast. The objective of this study was to determine if a 30‐ or 60‐d harvest frequency or 0, 110, or 220 kg N ha−1 fertilization could be managed to enhance crude protein (CP) yield and nutritive value of rhizoma peanut at three locations in Louisiana. Crude protein, neutral‐detergent fiber (NDF), in vitro true digestibility (IVTD), and digestible NDF (DNDF) were measured on ‘Florigraze’ rhizoma peanut grown at three Louisiana locations in 1997 and 1998. Nitrogen fertilization increased CP yield approximately 80 kg ha−1 for the 110 and 220 kg N ha−1 treatments at two locations in 1 of 2 yr. Nitrogen fertilization affected nutritive value at two harvests at two locations in 1998 only. However, nutritive value was consistently lower for 60‐d harvests than for 30‐d harvests and was more consistent. Rhizoma peanut harvested in 1997 at 30‐d intervals had 50 g kg−1 greater CP, 72 g kg−1 greater IVTD, and 40 g kg−1 greater DNDF coupled with 80 g kg−1 lower NDF than rhizoma peanut harvested at 60‐d intervals. Likewise, there were seasonal influences on nutritive value. Responses in CP yield and nutritive value observed in this study were influenced more by environment (primarily rainfall) than by N fertilization and harvest management.