Lower In Vitro Dry Matter Digestibility Research Articles

Management of Aries and Aruana Guinea grass cultivars under rotational stocking based on canopy light interception

AbstractEfforts were made to obtain forage cultivars with high production capacity and quality and to determine the ideal time to start animal grazing, respecting the morphological characteristics of the grasses. For this purpose, the nutritional value, digestibility and characteristics of the forage canopy of Aries and Aruana (Megathyrsus maximus (Jacq.) or Panicum maximum) cultivars kept under rotational stocking with sheep were evaluated and the management height was determined based on 95% light interception (LI). The experiment was evaluated with repeated measures over time (grazing cycles by season, in 2 years) with a treatment factor (grass cultivar) in a completely randomized block design with eight replicates, using 800 m2 paddocks. The height of the forage canopy before grazing (pre-grazing) determined by 95% LI stabilized around 29 cm. The highest proportion of Aruana leaf blades was observed in winter. Aries grass presented similar leaf blade percentages in summer, autumn and spring. Similar forage accumulation (FA) was observed for both cultivars, decreasing in spring, autumn and winter. Higher crude protein and in vitro dry matter digestibility (IVDMD) were seen in Aries grass, while Aruana grass presented higher neutral and acid detergent fibre and cellulose and lower IVDMD. The nutritional quality of the grasses was maintained throughout the year. The height of the forage canopy of Aries and Aruana recommended for entry into the paddock is 29 cm to maintain nutritional quality. The successful management strategy adopted for grasses combined with nitrogen fertilization provided a greater forage mass quality.

Cattle Grazing Effects on Phragmites australis in Nebraska

Phragmites australis (common reed) is one of the most widely distributed flowering plants in North America. The introduced lineage occurs in wetland and riparian areas covering a range of climatic types. In Nebraska, an abundance of livestock could help to reduce P. australis with proper timing and grazing intensities. In 2011, a 3-yr study was initiated to evaluate targeted cattle grazing and herbicide effects and the nutritive value of this species. Treatments included a single application of imazapyr (Habitat®, BASF Corporation, Research Triangle Park, NC) herbicide applied in the first year, grazing, and a control. Grazing was applied for up to five consecutive days in June and August 2011 and 2012 and in June 2013. Stem density, height, and biomass of P. australis were determined before each grazing period and in 2014. Diet samples were collected from rumenally fistulated steers each grazing period. Imazapyr provided 100% control of P. australis; however, re-establishment began 2 yr posttreatment. Grazing significantly reduced pregrazing P. australis biomass in the second and third growing season (P < 0.05). Stem density and height in the grazed treatment was similar to the control through 2012; however, in 2013 and 2014, control stem density was 1.5 times greater and height was 1.4 times that of the grazed treatment. Crude protein content of diet samples was greater in 2011 (16.8%) compared with 2012 (14.3%, P < 0.05). In vitro dry matter digestibility (IVDMD) of diet samples (45.4%) was not affected by year or month (P > 0.05). The relatively low IVDMD suggests that some form of energy supplementation would be needed to create a better nutritional balance. The cumulative effect of grazing does have the potential to reduce P. australis populations, but other methods would have to be used for greater control and site restoration.

Switchgrass Biomass Composition Altered by Six Generations of Divergent Breeding for Digestibility

ABSTRACTBiomass composition of switchgrass (Panicum virgatum L.) can affect its utilization by ruminants and its conversion to liquid fuels in a biorefinery. The objective of this study was to evaluate the effects of six generations of divergent breeding for forage in vitro dry matter digestibility (IVDMD) on switchgrass biomass composition, forage quality traits, and ethanol yield. Initially there was one cycle of selection for both low (C‐1) and high IVDMD (C1 = cv. Trailblazer), followed by four additional breeding cycles for high IVDMD. In cycles 4 and 5, winter survival was included as a selection criterion because of decreased winter survival of the C3 population. The experimental populations that were produced by these breeding generations and nine half‐sib families from cycle 5 were evaluated for two post‐establishment years at the research station in eastern Nebraska, where all the breeding work was conducted. The six breeding generations resulted in significant differences among the populations for all the 28 cell wall and non‐cell‐wall composition variables measured, forage quality, and ethanol yield traits measured except for total biomass C, cell wall concentration, soluble glucose, and etherified ferulates. These traits included all cell wall and nonstructural carbohydrates. Breeding for the heritable complex trait IVDMD affected a large number of plant biomass characteristics and also adversely affected plant biomass yield and winter survival.

Production and Nutritional Quality of low elevation zone Grasslands and Kermes Oak Shrublands (Quercus coccifera L.) in the South-East Mediterranean Basin

Problem statement: The objective of this study was to evaluate the production and nutrition quality of grasslands and kermes oak shrublands in Preveza Prefecture, northwest Greece. Approach: The study involved the collection of herbage and browse samples along a grazing period, from March to October for two consecutive years. In consequence, browse samples were manually separated to leaves and twigs. The three forage components (herbage, kermes oak leaves and twigs) were analyzed for crude protein, Neutral-Detergent Fiber (NDF), Acid-Detergent Fiber (ADF), lignin and In Vitro Dry Matter Digestibility (IVDMD). After the 2 years of observation, we concluded that kermes oak browse, especially the leaves, had CP content adequate to fulfill the nutrient requirements of grazing goats throughout the grazing period. Results: However, this browse is characterized by a very low IVDMD during summer, which may be the result of high lignin content and the presence of anti-nutritional factors such as phenols and tannins. The month of harvest strongly affected the production and nutritive value of forage components, firstly by giving a significant positive correlation among average monthly temperature, production, cell wall contents and secondly, a negative correlation among average monthly rainfall, IVDMD and lignin content. Conclusion: In closure, kermes oak shrublands of the lower zone constitute an important alimentary source providing adequate amounts of browse in order to maintain the nutrient requirements for grazing goats during the summer, when the herbage is not desirable for consumption from sheep and cattle.

VALOR NUTRITIVO DE GRAMÍNEAS FORRAGEIRAS TROPICAIS IRRIGADAS EM DIFERENTES ÉPOCAS DO ANO

Bromatological composition and in vitro dry matter digestibility (IVDMD) of six forage grasses, under different irrigation depths and seasons, were evaluated. The experiment was carried out in a completely randomized arrangement, with two replications, in a split-split plot design. Six grass species (Xaraés, Mombaça, Tanzânia, Pioneiro, Marandu, and Estrela) constituted the plots, six irrigation depths (0%, 18%, 45%, 77%, 100%, and 120% of the reference) the split-plots, and two seasons (autumn/winter and spring/summer) the split-split-plots. In order to vary irrigation depths, a line source sprinkler system was used. Raw protein (RP), neutral detergent fiber (NDF), and IVDMD were evaluated. Higher RP and IVDMD levels were found in autumn/winter and higher NDF in spring/summer. Irrigation depths affected Xaraés, Mombaça, and Estrela IVDMD, but did not affect their RP and NDF. Pioneiro presented higher RP and lower NDF, while Xaraés and Estrela presented higher and lower IVDMD, respectively. KEY-WORDS: Line source sprinkler system; neutral detergent fiber; raw protein.

Produção e composição química do leite, consumo e digestibilidade de forragens tropicais manejadas em sistema de lotação intermitente

Os objetivos neste trabalho foram comparar a composição química, a digestibilidade in vitro da matéria seca (DIVMS), as frações lâminas foliares e bainhas-colmos e a disponibilidade de forragem e avaliar a produção e composição do leite, o peso vivo, o escore corporal e o consumo de matéria seca de forrageiras tropicais. As forrageiras avaliadas foram capim-tanzânia (Panicum maximum Jacq.), grama-estrela (Cynodon nlemfuensis Vanderyst) e capim-marandu (Brachiaria brizantha Staf). As pastagens foram adubadas com nitrogênio (200 kg/ha.ano), K2O e P2O5 (50 kg/ha.ano) e manejadas em sistema de lotação intermitente com três dias de ocupação de piquete e dois intervalos de desfolha: janeiro e fevereiro com 24 dias e março, abril e maio com 30 dias. Foram utilizadas 24 vacas em delineamento de blocos ao acaso, com oito vacas por tratamento. As lâminas foliares da grama-estrela tinham em média 18,5% de PB e as bainhas-colmos, 79,9% de fibra em detergente neutro (FDN), valores superiores aos obtidos nas demais forrageiras. A grama-estela também apresentou maior teor de FDN (72,8%) e lignina (7,1%) na forragem disponível. A digestibilidade in vitro da matéria seca do capim-marandu (64,%) foi superior à da grama-estrela (59,4%). Nos capins-tanzânia e marandu, as produções de leite foram de 9,8, valor superior ao de 8,4 kg/vaca.dia da grama-estrela. O teor de proteína do leite das vacas manejadas no capim-tanzânia (2,9%) foi superior ao obtido com grama-estrela (2,8%), mas os teores de gordura e sólidos totais do leite, o escore corporal, o peso vivo e o consumo de matéria seca não diferiram entre as forrageiras avaliadas. A grama-estrela teve maior porcentagem das frações fibrosas, menor DIVMS e menor produção de leite em comparação aos capins-tanzânia e marandu.

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.

Avaliação qualitativa da pastagem diferida de Brachiaria decumbens Stapf., sob pastejo, no período da seca, por intermédio de três métodos de amostragem

O experimento foi conduzido para avaliar a qualidade da pastagem diferida de Brachiaria decumbens sob pastejo durante o período da seca, utilizando-se quatro novilhos Holandês-Zebu fistulados no esôfago. As amostras foram coletadas com base na disponibilidade total (DT), na simulação manual de pastejo (SMP) e na extrusa (EXT) coletada. Foram determinados os teores de matéria seca (MS), proteína bruta (PB), extrato etéreo (EE), matéria mineral (MM), carboidratos totais (CT) e não-fibrosos (CNF), fibra em detergente neutro (FDN), fibra em detergente neutro isenta de cinzas e proteínas (FDNcp), fibra em detergente ácido (FDA), fibra em detergente ácido indigestível (FDAi), lignina e digestibilidade in vitro da matéria seca (DIVMS). As amostras obtidas com a DT apresentaram valores superiores para MS, CT, FDN, FDNcp, FDA, FDAi e lignina, que refletiram na menor DIVMS para a DT. A EXT e a SMP não diferiram quanto à PB, EE, CNF, FDN, FDNcp, FDA, FDAi, lignina e DIVMS. Os teores de PB foram 5,60 e 6,50 e os de FDN foram 71,87 e 71,70, respectivamente, para a SMP e a EXT. Os resultados sugerem que a amostra obtida pela SMP, em comparação com a DT, estaria mais próxima da forragem selecionada por animais em pastejo.

Vegetation diversity, growth, quality and decomposition in managed grasslands

The relationship between vegetation growth rate, quality, litter decomposition and diversity was investigated in four grazed grasslands differing in topography, management and fertility in the southern North Island of New Zealand. Vegetation samples were clipped at two sampling times (summer and autumn) from 0.5 m 2 areas excluded from grazing. Crude protein (CP), in vitro dry matter digestibility (IVDMD), neutral detergent fiber (NDF), average daily growth (ADG) rate, species composition and the relative extent of tissue degradation by soil microorganisms were determined for the vegetation samples. It was hypothesized that vegetation diversity would be negatively related with measures of vegetation growth, quality and decomposition. Comparisons made across all environmental and management conditions agreed with the hypotheses. Higher vegetation diversity was associated with lower ADG rate, lower CP concentrations, lower IVDMD and higher NDF concentrations. Comparisons within management regimes (MR), however, were less consistent and possible reasons for this are examined. Litter decomposition extent was closely related to the tissue quality characteristics of the vegetation, especially NDF concentration, but not species diversity. The observed local-scale relationships between the vegetation diversity, growth, quality and decomposition characteristics were contended to be largely the result of the influence of environmental resource richness on community structure of the managed grasslands studied. There is a need to promote a functionally diverse plant community over the entire managed area rather than promoting high localized species diversity within grasslands.

The chemical composition and in vitro dry matter digestibility of untreated and ammoniated crop residues

The chemical composition and in vitro dry matter digestibility (IVDMD) of untreated and ammoniated crop residues, sampled at various sites in the North West Province of South Africa, were investigated. The mean IVDMD of maize residues obtained by means of a whole plant maize harvester was found to be relatively high (IVDMD = 55.6±7.0%) while the crude protein (CP) (46±10 g/kg dry matter (DM)) and phosphorus (P) (1.2±0.5 g/kg DM) concentrations were below the maintenance requirement for dry gestating beef cows. The neutral detergent fibre (NDF) concentration was 837±39 g/kg DM. Maize residues obtained by means of a cob harvester tended to be of a somewhat higher nutritional quality (IVDMD = 58.3±7.7%; CP = 64±19 g/kg DM; NDF = 817±42 g/kg DM; P = 1.2±0.6 g/kg DM). Grain-sorghum residues, like maize residues, were low in CP (61±11 g/kg DM) and P (1.9±0.5 g/kg DM) concentration, but also had a low IVDMD (37.7±9.3%). Ammoniation (35 g ammonia/kg DM, 320 g moisture/kg DM) increased the IVDMD (17.6 and 18.1 percentage units) and CP concentration (89 and 93 g/kg DM) and decreased the NDF concentration (207 and 148 g/kg DM) of maize- and grain- sorghum residues, respectively. The IVDMD (71.5±6.2%) and NDF concentration (380±73 g/kg DM) of sunflower-cob residues reflected a high-energy value while the CP (93±26 g/kg DM) and P (2.2±0.7 g/kg DM) concentration met the needs for dry gestating beef cows. Ammoniation increased the CP concentration (186±21 g/kg DM), but had no effect on the IVDMD and NDF concentration of sunflower-cob residues. South African Journal of Animal Science Vol.32(2) 2002: 83-88

Comparison of the digestive ability of crop fluid from the folivorous Hoatzin ( Opisthocomus hoazin) and cow rumen fluid with seven tropical forages

We explored the hypothesis that the Hoatzin, a tropical bird which feeds on tree leaves and has a crop resembling a rumen, may have a better ability to digest tanniniferous feeds than do cattle. Comparisons were made between Hoatzin crop fluid (HCF) and cow rumen fluid (CRF) in in-vitro digestion studies using freeze dried leaves of six tropical tanniniferous shrub legumes and the tropical grass Panicum maximum. In-vitro dry matter digestibility (IVDMD) and in-vitro nitrogen digestibility (IVND) were measured in the presence and absence of polyethylene glycol (PEG) to minimise the effect of condensed tannin. For all plant species, and in the presence or absence of PEG, the CRF gave higher IVDMD and IVND than did HCF ( P<0.01). The interaction of PEG×animal ( P<0.01) for IVDMD was due to an absence of response with CRF (62.1 v 63.0%) and a large response with HCF (43.5 v 37.4%). Similarly for IVND, the response to PEG with CRF was much smaller (83.4 v 75.6%) than for HCF (51.9 v 26.5%) ( P<0.01). PEG had no significant effect on IVDMD or IVND of the CT-free Panicum maximum by HCF or CRF ( P>0.05). However, values were much higher with CRF: 74.2 v 30.6% and 81.3 v 29.0%, respectively. The only legume to have reasonable levels (>55%) of IVDMD and IVND with HCF in the absence of PEG was Gliricidia sepium, which has little or no free condensed tannins. Acacia boliviana, Calliandra calothyrsus and Leucaena trichandra gave low values and those for L. leucocephala and L. pallida were intermediate. The low IVDMD and IVND with HCF, together with the large response to PEG, clearly show that high tannin content in the diet cannot be handled by the Hoatzin. Low tannin content in the crop contents indicates that it avoids highly tanniniferous leaves. This supports other findings that the Hoatzin is extremely selective of a high quality leafy diet. It is concluded that the Hoatzin is an unlikely source of bacteria to improve the feeding value of tropical tanniniferous shrub legumes for cattle.

Chemical composition and in vitro dry matter digestibility of four parasitic plants ( Tapinanthus lugardii, Erianthenum ngamicum, Viscum rotundifolium and Viscum verrucosum) in Botswana

Parasitic plants, Tapinanthus lugardii, Erianthenum ngamicum, Viscum rotundifolium and V. verrucosum were harvested during months (January, March, May and June) in 1998 at the Sebele Research Station. The samples were separated into leaves and stems, (first 15–20 cm of shoots) or used as whole plants and analysed for crude protein (CP), acid detergent fibre (ADF), acid detergent lignin (ADL) and minerals. In vitro dry matter digestibility (IVDMD) was determined. There was a significant ( p<0.05) month and species effect on CP. The month effect assumed a linear ( p<0.01) response. The CP increased from the first month (January) of sampling to a maximum at the last month (June) of sampling and ranged from 104 to 206 g/kg DM. Although the month effect was not significant ( p>0.05) on minerals, Cu increased in a linear ( p<0.05) fashion from the first month to the last month of sampling, while the reverse was true for Ca. The species V. rotundifolium had significantly ( p<0.01) higher CP than E. ngamicum (163 vs. 125 g/kg DM). There were significant species influences on Cu ( p<0.05) and Zn ( p<0.01). V. rotundifolium had higher Cu and Zn than the other species. Crude protein (182, 125, and 98 g/kg DM), ADF (208, 332 and 402 g/kg DM), IVDMD (59.1, 41.3 and 33.8% DM), Fe (205, 112 and 95 ppm) differed significantly ( p<0.01) between leaves, whole plant and stems of E. ngamicum. There were also significant ( p<0.05) differences between leaves, whole plant and stems of E. ngamicum for Ca, Mn, Zn and ADL, except Cu and P. Higher levels of Ca, Mn and Zn were found in the leaves than in the stems, while the converse was true for ADL. Plant fractions of T. lugardii differed significantly for ADF (219, 265 and 357 g/kg DM; p<0.01), ADL (91, 107 and 150 g/kg DM; p<0.05), IVDMD (48.8, 46.7 and 34.6%; p<0.01), and Zn (20, 21.8 and 30.3 ppm; p<0.05) in the leaves, whole plant and stems respectively. Crude protein, Ca, P, Cu, Fe and Mn were not significantly ( p>0.05) different among the plant fractions of. T. lugardii. For the species T. lugardii and E. ngamicum, the stems had high content of fibre and lignin but low IVDMD. Although there was variation in chemical composition among the species and months, the levels of nutrients were constantly higher than what is expected in natural grasses, especially during the dry season. This suggests that these parasitic plants can be effectively used as nutrient supplements.

Forage Quality of Selected Cool-Season Weed Species

Forage quality was determined at vegetative, flowering, and fruiting stages for nine cool-season weed species and four cultivated forages. When compared at the vegetative stage of maturity, Carolina geranium (Geranium carolinianumL. # GERCA), Virginia pepperweed (Lepidium virginicumL. # LEPVI), Virginia wildrye (Elymus virginicusL. # ELYVI), wild oats (Avena fatuaL. # AVEFA), cheat (Bromus secalinusL. # BROSE), and little barley (Hordeum pusillumNutt. # HORPU) had high nutritive quality as indicated by in vitro dry-matter digestibility (IVDMD) values equal or superior to rye (Secale cerealeL.), tall fescue (Festuca arundinaceaSchreb.), and ladino clover (Trifolium repensL.). Cutleaf evening primrose (Oenothera laciniataHill # OEOLA) and curly dock (Rumex crispusL. # RUMCR) had lower IVDMD values than the cultivated forages and all weed species except wild oats. However, the rate of decline in IVDMD as plants matured was generally greater for the weed species compared to cultivated forage plants. All weed and cultivated forage species had adequate levels of Ca and K for livestock. Nearly all weed and cultivated forage species had suboptimum levels of P for high-producing ruminant animals; Carolina geranium and cutleaf evening primrose had high Ca:P ratios, which can cause metabolic disorders. Carolina geranium, Virginia wildrye, wild oats, cheat, little barley, and all the cultivated forage species had inadequate levels of Mg and could be considered “tetany prone”. Most of the forbs had high Mg concentrations.

Structural changes in wheat straw components during decay by lignin‐degrading white‐rot fungi in relation to improvement of digestibility for ruminants

AbstractStructural changes and resulting in‐vitro dry matter digestibility (IVDMD) were determined during the course of solid‐state fermentation of wheat straw using the lignin‐degrading white‐rot fungi Sporotrichum pulverulentum, Pycnoporus cinnabarinus and Cyathus stercoreus. The first fungus grew very rapidly on straw but degraded hemicelluloses and cellulose non‐selectively resulting in very low IVDMD increases (50% after 35% weight loss). P. cinnabarinus and C. stercoreus preferentially degraded hemicelluloses achieving high improvements in IVDMD (maximum increase of 63 and 94%, respectively) with limited dry weight losses (12 and 18% after 7 and 13 days, respectively). The three fungi exhibited some selectivity among the individual hemicellulose components: O‐acetyls were removed essentially at the same rate as xylan, while uronic acids accumulated as incubation proceeded. Conversely, the arabinose content decreased rapidly, especially with C. stercoreus and P. cinnabarinus, suggesting that removal of this pentose was partly responsible for digestibility improvement. Esterified phenolic acids were rapidly degraded during the first stages of decay by all three fungi although P. cinnabarinus and C. stercoreus degraded ferulic acid faster than p‐coumaric acid. Lignin was preferentially degraded compared to polysaccharides by all three fungi. The amount of lignin removed, as determined by Klason, correlated well with IVDMD improvement (r=−0.97), while acid detergent lignin (ADL) showed a lower correlation (r=‐0.86). Acidolysis yields of decayed lignin pointed to preferential degradation of β‐O‐4 ether linked units by the fungi. Syringyl units were removed faster than guaiacyl units only after 5 to 10% weight loss was obtained.

Anatomical Characteristics of Smooth Bromegrass Clones Selected for In Vitro Dry Matter Digestibility1

Digestibility plays an important role in forage nutritive value. Anatomical components have repeatedly been demonstrated to influence digestibility of forage crops. Eighteen clones of smooth bromegrass (Bromus inermis Leyss.) selected for either high or low in vitro dry matter digestibility (IVDMD) were evaluated determine if adequate genotypic variation existed for anatomical and chemical components and their relationship with IVDMD. Clones were planted in five randomized complete blocks at Arlington, WI (Piano silt loam—fine‐silty, mixed, mesic Typic Argiudoil) in August 1981. In June 1982, when the clones were just 100% headed, whole‐plant, leaf and stem material were collected for evaluation of IVDMD, neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent linguine, insoluble ash, and anatomical components of stems and leaves. A cryostat was used to cut 12 μm sections of leaf and stem material for estimation of percentage tissue types. High IVDMD clones had significantly greater percentages of the most readily digestible tissue types (stem chlorenchyma and leaf mesophyll), a significantly lower percentage of lignified leaf vascular tissue, and thicker stems than the low IVDMD clones. Reduced genotypic variation within the high IVDMD group of clones was observed for IVDMD and most anatomical components compared to variation among the low IVDMD clones. Significant variation for NDF, ADF and cellulose was detected among the high IVDMD clones. Continued gains from selection for improve digestibility within the population derived from the nine high IVDMD clones may be difficult due to the narrowed genetic base for IVDMD and stem and leaf anatomy, but selection for improved dry matter intake potential appears to have some merit.

Divergent Selection for In Vitro Dry Matter Digestibility in Switchgrass1

The purposes of this study were to determine if phenotypic selection for in vitro dry matter digestibility (IVDMD) could be used to improve the IVDMD for switchgrass (Panicum virgatum L.) and to obtain heritability estimates of IVDMD in switchgrass. In 1973 a selection nursery of over 2,200 plants was established with transplanted seedlings of two similar Nebraska experimental strains. In 1974 about 800 plants that appeared to be agronomically superior were sampled for IVDMD. Single‐plant selectlons for high and low IVDMD were made in each of the nursery rows. In 1976, ramets from 25 of the high‐IVDMD selections and from 25 of the low‐IVDMD selections were transplanted to establish isolated high‐ and low‐ IVDMD polycross (PC) nurseries. Seed harvested from these nurseries in 1977 and from the same openpollinated (OP) clones in the selection nursery in 1976 was used in 1978 to establish a replicated seeded sward nursery in which the following strains were compared: high IVDMD PC, high IVDMD OP, ‘Pathfinder,’ low IVDMD OP, and low IVDMD PC. Forage yields and IVDMD were measured in 1978 and 1979. Over the 2 years the strains averaged 51.5, 50.0, 49.4, 48.3, and 48.1% IVDMD, respectively. The high IVDMD PC strain was significantly higher in IVDMD than the other strains in both years. Realized heritabilities for high and low IVDMD were 0.59 and 0.55, respectively. Strains did not differ significantly for forage yield in either year; thus, the gain in IVDMD by breeding was achieved without any yield loss.

Histological and in vitro Digestion Study of 1‐ and 4‐Week Stems and Leaves From High and Low Quality Bermudagrass Genotypes1

AbstractAnatomical information is limited on changes occurring with age of the forage and differences due to genotype affecting in vitro dry matter digestibility (IVDMD). Since this type of information would be ot value to those concerned with the production and use of forage, two bermudagrass, Cynodon dactylon (L.) Pers., clones with high IVDMD values (Coastcross‐1 and P.I. 293603) and two clones with low IVDMD values (P.I. 291715 and P.I. 291719) were studied histologically. No histological differences were observed in either the stems or leaves between the high‐ and low‐quality bermudagrass of the same age. The formation of a band of thick‐walled cells in the stem at 4 weeks of age more than doubled the percentage of anatomical components resistant to 72 hours of rumen fluid digestion and reduced IVDMD values by up to 44%, as compared to 1‐week‐old stems. The percentage of anatomical components resistant to digestion in the leaves and IVDMD values of leaves remained relatively the same in 1 and 4‐week‐old samples of a specific clone. This indicates that reduction in quality with age of bermudagrass forage is due mainly to changes occurring in the stem. The vascular bundles (except phloem), parts of the epidermal cells, and the thick‐walled cells in 4‐week‐old stems were resistant to digestion. The higher IVDMD values of the high‐quality bermudagrasses appear to be due to a larger soluble fraction and more digestible cell wall. No anatomical differences were observed between the high and low quality genotypes to account for the differences in IVDMD values.

THE IN VITRO DIGESTIBILITY OF WHOLE GRASSES AND THEIR PARTS AT PROGRESSIVE STAGES OF MATURITY

The in vitro dry matter digestibility (IVD) of timothy, orchard, brome, reed canary, tall fescue and mountain rye grasses decreased at the rate of approximately 0.5 per cent per day throughout the growing season. The most rapid decline in IVD began with head emergence. The earliest maturing grasses tended to be higher in IVD than the other grasses at the flowering stage. The decline in IVD as the season progressed was observed in all portions of the plant, the rate of decline for the heads and stems being greater than for the leaves. The upper segments of the stems tended to have a lower IVD than the basal segments.