No abstract

Chemical and in vitro characteristics of six perennial summer grasses {common, ‘Coastal’ and ‘Coastcross‐1’ bermudagrasses [Cynodon dactylon (L.) Pers.]; ‘Pensacola’ bahiagrass [Paspalum notatum Flugge]; common weeping lovegrass [Eragrostis curvula (Schrad.) Nees.]; and ‘Kleingrass 75’ [Panicum coloratum L.]} were determined to identify factors limiting the performance of grazing animals. In vitro dry‐matter digestibility (IVDMD), cell wall content (CWC), acid‐detergent fiber (ADF), acid‐detergent lignin (ADL), silica, and in vitro cell‐wall digestibility (IVCWD) were determined for samples of available forage taken at 14‐day intervals. Animal performance was obtained from yearling heifers grazing established stands of each grass. Available forage was estimated from strips harvested from each pasture at 2‐ to 4‐week intervals. Animal performance was significantly correlated (r = 0.85**) with available forage when dry‐matter digestibility was relatively uniform. As IVDMD of available forage decreased, more available forage was required to reach maximum average daily gain (ADG). Also, as IVDMD decreased, maximum ADG decreased. The CWC of the grasses ranged from 45 to 82% with cell wall digestibility ranging from 82 to 36%, respectively. CWC and IVDMD were significantly correlated with animal performance (r = —0.80**, and 0.78**, respectively). Cell wall digestibility calculated from Van Soest's “summative equation” significantly over‐estimated IVCWD. Lignification was one factor limiting cell wall digestibility (r = —0.76**) and in Coastcross‐1 bermudagrass and Pensacola bahiagrass silica was as important as lignin. CWC and IVCWD could be used to accurately predict IVDMD in Kleingrass 75 (r = —0.96** and 0.95** respectively). High lignin and/or silica content of available forage was associated with poor animal perfortnance on all grasses.

No abstract

Soybeans [Glycine max (L.) Merr.] are known to have potential for hay production but additional cultural and harvest practice information is needed to optimize production and forage quality. Nodulating ‘Lee’ cv. of soybeans was grown on Ships clay (very fine, thermic, Udertic Haplustolls) at densities of 97,100, 194,200 and 291,300 plants/ha in 68‐cm row widths to evaluate the effect of stage of maturity at harvest and planting density on the quality (percent digestibility and crude protein) and dry matter yield of the soybean hay. The plant tops were separated into leaflets, stems plus petioles, and pods plus grain. Dry weight, in vitro dry matter digestibility (IVDMD) and crude protein (percent N ✕ 6.25) were determined for each sample. Plant density had a small negative effect on IVDMD, a large positive effect on dry matter (DM) yield and no significant effect on the percent crude protein of the soybean plant. Age had a significant effect on the proportion and DM production of plant components, IVDMD of leaves and stems but not pods and total plant, and protein content. When the pods were filled and leaves were beginning to turn yellow, the percentages of leaves, stems, and pods were 28, 36, and 36, respectively with a total DM yield of 12.4 metric ton/ha. The highest protein (20.2%) and IVDMD (62.2%) values for the total plant were at the pod‐filled stage. For optimum yield, crude protein and digestibility, the best time to cut soybean for hay appears to be when pods are filled and some leaves are starting to turn yellow.

Wheat (Triticum aestivum L. em Thell.) is commonly both grazed for forage and harvested for grain in the Southern Great Plains of the USA. Information is needed on the plant characteristics affected by forage removal and their relationships to grain yield. Leaf area index was measured at 0,1, and 2 weeks following forage removal in 3 years of field experiments. The soil type was a member of the fine, montmorillonitic thermic family of Vertic Albaqualfs. Leaf area and dry matter present at anthesis were also recorded. Treatments consisted of taking the final forage harvest for two cultivars at the early joint, mid‐joint, or late joint stage of development but without removing terminal meristems. All treatments were harvested for grain at maturity, including a check that was not harvested for forage. Total LAI at anthesis averaged over varieties for the first 2 years, decreased from 1.40 to 0.79 when the final forage harvest was delayed from early to late joint. Total dry matter present at anthesis averaged over all years and varieties decreased from 491 to 326 g m−2. Leaf area duration from jointing to anthesis, the product of the average leaf area present and the number of days in the sampling period, averaged 42.9 days m2m−2 for the early joint treatment, compared to 15.8 days m2m−2 for the plants harvested at late joint. These factors were highly correlated (r = 0.64 to 0.88) with grain yield in all 3 years for both cultivars. The data indicate that when the leaf area produced during the vegetative and jointing stages was harvested as forage, grain yield was limited by the potential of the plant to rapidly produce new leaf area and prevent tiller senescence during the period between jointing and anthesis.

Several selections of bermudagrass and other turfgrass species were evaluated for turf quality characteristics under different levels of light intensity. Light levels of approximately 35, 60, and 100% and 25, 35, and 100% of incident light, respectively, were used in two independent studies. A variety of bermudagrass, ‘No‐Mow (FB‐137)’, exhibited exceptional tolerance to low light intensity. Turf quality of No‐Mow was better when grown under reduced light than when exposed to full sunlight. No‐Mow also exhibited more shade tolerance than Common St. Augustinegrass. Bermudagrass selection T‐135 showed some tolerance to shading but less than No‐Mow. Other grasses, including Pensacola bahiagrass, Meyer zoysia, and two additional varieties of bermudagrass, generally were unsatisfactory.

Bermudagrass [Cynodon dactylon (L.) Pers.] is a major warmseason perennial grass grown on improved pastures in the South. Available forage and its digestibility vary widely in a normal grazing season on bermudagrass pasture. A method is needed to predict steer (Bos sp.) gains from the amount and digestibility of available forage. Five bermudagrass cultivars differing in digestibility were grazed at different grazing pressures to produce four levels of available forage. Forage was classified by concentration of in vitro digestible dry matter (IVDDM) as high (>600 g kg−1 IVDDM), medium (530 to 600 g kg−1 IVDDM), or low ( <530 g kg−1 IVDDM) digestibility. At each level of IVDDM, average daily gain (ADG) of steers was fitted to an asymptotic function of available forage. On high, medium, and low digestibility forages, approximate asymptotic ADG values were 0.94, 0.74, and 0.31 kg, and 68,83, and 89 g forage kg−1 body weight day−1, respectively, were needed to produce the asymptotic ADG values. For steers to maintain their weight on high, medium, and low digestibility forage, 14,18, and 43 g forage dry matter kg−1 body weight day−1, respectively, must be present. Because the quantities of available forage required for maximum steer gains or even for maintenance were far in excess of what the steers could physically consume, it appears that opportunity for selective grazing is necessary.

SummaryWe previously reported that culture of murine fetal liver (FL) cells with interleukin 7 (It-7) results in expression of high levels of T cell receptor (TCR) y transcripts by a population of cells expressing Thy-1 and Pgp-1, suggesting that IL-7 promotes the growth and/or differentiation of pre-T cells. We demonstrate herein that culture of FL cells for 7 d with IL-7 caused the rearrangement and expression of TCR y variable (V) region genes Vy4 and Vy6, but not' Vy5 or Vy7. Since this effect was not blocked by hydroxyurea, it appeared to represent induction of expression of these genes by IL-7 rather than expansion of a preexisting positive population.We also show that IL-7 induced RAG-1 and RAG-2 mRNA expression by FL cells. These data provide evidence that specific TCR y/S V region genes can be rearranged and expressed by T lineage cells before their migration to the thymus, in response to IL-7 .