Rotation Grazing Demonstrations With Beef Cows on HEL - Adams County Conservation Reserve Program (CRP) Project

Two grazing systems were demonstrated on Conservation Reserve Program (CRP) land in southwestern Iowa near Corning in the summers of 1991, 1992, 1993, 1994, and 1995. This report summarizes the 1995 data and compares them to results from the four previous years. The systems, a 13-paddock intensive-rotational grazing system and a 4-paddock more traditional rotation, both established in 1991, are aimed at showing economically sustainable grass alternatives for steeply sloping (9-14% slope), highly erodible land (HEL) once the 10-year CRP ends. In a 147-day grazing season in 1995, nursing crossbred calves with no creep gained 2.36 pounds and 2.38 pounds per day on the 13- and 4-paddock systems, respectively. The rotations were stocked at 1.65 acres per cow-calf pair on the 13-paddock system and 1.72 acres per pair on the 4-paddock system. This produced 210.2 pounds of calf gain per acre on the 13-paddock system and 203.2 pounds of calf gain per acre on the 4- paddock system.. Similar calves gained 2.37 pounds and 2.50 pounds per day for 155 days, yielding a total gain per acre of 222.7 pounds on the 13-paddock system and 224.9 pounds on the 4-paddock system in 1994. Results for 1992 remain the highest from both systems in the five years of grazing, with calf gain per head per day at 2.45 for 155 days netting 241.9 pounds per acre on the 13- paddock system and calf gain per head per day at 2.38 for 154 days on the 4-paddock system yielding 263.6 pounds per acre. Cows maintained both their weight and condition scores in both systems again in 1995. A third system, the 18-paddock intensive-rotational grazing system, was stocked with stocker steers in 1995, and the results are reported in a second article in the 1996 ISU Beef Research Report entitled “Intensive- Rotational Grazing Steers on Highly Erodible Land at the Adams County CRP Project.” Concerning grazing management, paddocks were grazed four, five, or six times in the 13-paddock intensive- rotational grazing system during the 147-day grazing season of 1995. This number of times grazed per paddock was nearly equal to times grazed per paddock in 1994. However, several paddocks were subdivided temporarily to equalize paddock size and increase grazing uniformity. This increased the total number of cattle moves in the 13-paddock system from 78 in 1994 to 109 in 1995. The average length of stay on each paddock or subdivision of a paddock per grazing time was 1 to 2.2 days. This was less than in any of the other four grazing years in this project. The principle of not grazing more than half the standing forage during any one grazing period was closely followed in 1995. All paddocks in the 13-paddock system were also rested approximately the recommended 30 days between each grazing cycle in 1995.

Embedding of human vertebral bodies leads to higher ultimate load and altered damage localisation under axial compression

Computer tomography (CT)-based finite element (FE) models of vertebral bodies assess fracture load in vitro better than dual energy X-ray absorptiometry, but boundary conditions affect stress distribution under the endplates that may influence ultimate load and damage localisation under post-yield strains. Therefore, HRpQCT-based homogenised FE models of 12 vertebral bodies were subjected to axial compression with two distinct boundary conditions: embedding in polymethylmethalcrylate (PMMA) and bonding to a healthy intervertebral disc (IVD) with distinct hyperelastic properties for nucleus and annulus. Bone volume fraction and fabric assessed from HRpQCT data were used to determine the elastic, plastic and damage behaviour of bone. Ultimate forces obtained with PMMA were 22% higher than with IVD but correlated highly (R2 = 0.99). At ultimate force, distinct fractions of damage were computed in the endplates (PMMA: 6%, IVD: 70%), cortex and trabecular sub-regions, which confirms previous observations that in contrast to PMMA embedding, failure initiated underneath the nuclei in healthy IVDs. In conclusion, axial loading of vertebral bodies via PMMA embedding versus healthy IVD overestimates ultimate load and leads to distinct damage localisation and failure pattern.

Human intervertebral disc stiffness correlates better with the Otsu threshold computed from axial T2 map of its posterior annulus fibrosus than with clinical classifications

Degeneration of the intervertebral disc, sometimes associated with low back pain and abnormal spinal motions, represents a major health issue with high costs. A non-invasive degeneration assessment via qualitative or quantitative MRI (magnetic resonance imaging) is possible, yet, no relation between mechanical properties and T2 maps of the intervertebral disc (IVD) has been considered, albeit T2 relaxation time values quantify the degree of degeneration. Therefore, MRI scans and mechanical tests were performed on 14 human lumbar intervertebral segments freed from posterior elements and all soft tissues excluding the IVD. Degeneration was evaluated in each specimen using morphological criteria, qualitative T2 weighted images and quantitative axial T2 map data and stiffness was calculated from the load-deflection curves of in vitro compression, torsion, lateral bending and flexion/extension tests. In addition to mean T2, the OTSU threshold of T2 (TOTSU), a robust and automatic histogram-based method that computes the optimal threshold maximizing the distinction of two classes of values, was calculated for anterior, posterior, left and right regions of each annulus fibrosus (AF). While mean T2 and degeneration schemes were not related to the IVDs' mechanical properties, TOTSU computed in the posterior AF correlated significantly with those classifications as well as with all stiffness values. TOTSU should therefore be included in future degeneration grading schemes.

Computational and experimental methodology for site-matched investigations of the influence of mineral mass fraction and collagen orientation on the axial indentation modulus of lamellar bone

Relationships between mineralization, collagen orientation and indentation modulus were investigated in bone structural units from the mid-shaft of human femora using a site-matched design. Mineral mass fraction, collagen fibril angle and indentation moduli were measured in registered anatomical sites using backscattered electron imaging, polarized light microscopy and nano-indentation, respectively. Theoretical indentation moduli were calculated with a homogenization model from the quantified mineral densities and mean collagen fibril orientations. The average indentation moduli predicted based on local mineralization and collagen fibers arrangement were not significantly different from the average measured experimentally with nanoindentation (p=0.9). Surprisingly, no substantial correlation of the measured indentation moduli with tissue mineralization and/or collagen fiber arrangement was found. Nano-porosity, micro-damage, collagen cross-links, non-collagenous proteins or other parameters affect the indentation measurements. Additional testing/simulation methods need to be considered to properly understand the variability of indentation moduli, beyond the mineralization and collagen arrangement in bone structural units.

Determination of the Weak Axial Vector Coupling λ=g_{A}/g_{V} from a Measurement of the β-Asymmetry Parameter A in Neutron Beta Decay

We report on a new measurement of the neutron beta-asymmetry parameter A with the instrument \perkeo. Main advancements are the high neutron polarization of P=99.7(1) from a novel arrangement of super mirror polarizers and reduced background from improvements in beam line and shielding. Leading corrections were thus reduced by a factor of 4, pushing them below the level of statistical error and resulting in a significant reduction of systematic uncertainty compared to our previous experiments. From the result A0=−0.11996(58), we derive the ratio of the axial-vector to the vector coupling constant λ=gA/gV=−1.2767(16)

{\it Hox\/} genes and specification of regional identity in the axial skeleton: Analysis of the individual and combined mutant phenotypes of the paralogous group 4 murine {\it Hox\/} genes; {\it hoxa\/}-4, {\it hoxb\/}-4 and {\it hoxd\/}-4

The Hox gene products are transcription factors involved in specifying regional identity along the anteroposterior body axis. In Drosophila, where these genes are known as HOM-C (Homeotic-complex) genes and where they have been most extensively studied, they are expressed in restricted domains along the anteroposterior axis with different anterior limits. Genetic analysis of a large number of gain- and loss-of-function alleles of these genes has revealed that these genes are important in specifying segmental identity at their anterior limits of expression. Furthermore, there is a functional dominance of posterior genes over anterior genes, such that posterior genes can dominantly specify their developmental programs in spite of the expression of more anterior genes in the same segment. In the mouse, there are four clusters of HOM-C genes, called Hox genes. Thus, there may be up to four genes, called paralogs, that are more highly homologous to each other and to their Drosophila homolog than they are to the other mouse Hox genes. The single mutants for two paralogous genes, hoxa-4 and hoxd-4, presented in this dissertation, are similar to several other mouse Hox mutants in that they show partial, incompletely penetrant homeotic transformations of vertebrae at their anterior limit of expression. These mutants were then bred with hoxb-4 mutants (Ramirez-Solis, et al. 1993) to generate the three possible double mutant combinations as well as the triple mutant. The skeletal phenotypes of these group 4 Hox compound mutants displayed clear alterations in regional identity, such that a nearly complete transformation towards the morphology of the first cervical vertebra occurs. These results suggest a certain degree of functional redundancy among paralogous genes in specifying regional identity. Furthermore, there was a remarkable dose-dependent increase in the number of vertebrae transformed to a first cervical vertebra identity, including the second through the fifth cervical vertebrae in the triple mutant. Thus, these genes are required in a larger anteroposterior domain than is revealed by the single mutant phenotypes alone, such that multiple mutations in these genes result in transformations of vertebrae that are not at their anterior limit of expression. ^