Development of an in situ procedure to evaluate the reticulo-rumen morphology of sheep selected for divergent methane emissions.

Published studies have shown that methane yield (g CH4/kg dry matter) from sheep is positively correlated with the size (volume and surface area) of the reticulo-rumen (RR) and the weight of its contents. However, the relationship between CH4 yield and RR shape has not been investigated. In this work, shape analysis has been performed on a data set of computerised tomography (CT) scans of the RR from sheep having high and low CH4 yields (n=20 and n=17, respectively). The three-dimensional geometries of the RRs were reconstructed from segmented scan data and split into three anatomical regions. An iterative fitting technique combining radial basis functions and principal component (PC) fitting was used to create a set of consistent landmarks which were then used as variables in a PC analysis to identify shape variation within the data. Significant size differences were detected for regions corresponding to the dorsal and ventral compartments between sheep with high and low CH4 yields. When the analysis was repeated after scaling the geometries to remove the effect of size, there was no significant shape variation correlating with CH4 yield. The results have demonstrated the feasibility of CT-based computational shape determination for studying the morphological characteristics of the RR and indicate that size, but not shape correlates with CH4 yield in sheep.

The murine local lymph node assay: results of an inter-laboratory trial.

The local lymph node assay is a novel predictive test for the identification of contact allergens. The collaborative study reported here was performed to evaluate the reliability of the method when performed in independent laboratories. Eight chemicals were examined in each of 4 participating laboratories and results compared with predictions of skin-sensitizing activity made from concurrent Magnusson and Kligman guinea-pig maximization tests performed in a single laboratory. The local lymph node assay has as its theoretical basis the fact that contact allergens induce T-lymphocyte proliferative responses. In practice, predictions of contact-sensitizing potential are made following measurement of proliferation in lymph nodes draining the site of exposure to chemical, and derivation of a stimulation index using control values as the comparator. Although in the present study there was some variation between laboratories with respect to the absolute stimulation indices recorded, it was found that with all chemicals each laboratory made the same predictions of sensitizing activity. Six chemicals (2,4-dinitrochlorobenzene, formalin, eugenol, isoeugenol, p-phenylenediamine and potassium dichromate) yielded positive responses, and two (methyl salicylate and benzocaine) were negative, in each laboratory. Furthermore, with 7 of the 8 chemicals tested there was no significant difference between laboratories in terms of the characteristics of the dose-response relationships recorded. With the exception of one chemical (benzocaine), predictions made with the local lymph node assay were in accord with those derived from guinea-pig maximization tests. These inter-laboratory comparisons demonstrate that the local lymph node assay is a robust and reliable method for the identification of at least moderate and strong contact allergens.

The local lymph node assay: results of a final inter-laboratory validation under field conditions.

The local lymph node assay (LLNA) assesses the sensitizing activity of chemicals by measurement of primary lymphocyte proliferation in lymph nodes draining the site of application. In this final inter-laboratory study the consistency of LLNA results between laboratories and with guinea pig maximization test (GPMT) data was examined under 'field' conditions. Nine chemicals were evaluated independently by each laboratory according to guidelines for test concentration and vehicle selection developed during previous validation studies to ensure assay optimization. Equivalent predictions of sensitization potential were obtained by all laboratories for eight chemicals. Five of seven chemicals identified as sensitizers in the GPMT were correctly identified in the LLNA--four by all laboratories and 1 (4-chloroaniline) by one laboratory only--although in this latter case, two other laboratories obtained clear dose responses, suggestive of sensitization. The LLNA identified correctly those chemicals predicted to be extreme or strong sensitizers in the GPMT. The remaining two chemicals were non-sensitizers in the guinea pig and failed to elicit positive proliferative responses in the LLNA. These data demonstrate that sensitivity and reliability of the LLNA is retained when chemicals are evaluated independently, and that it provides a reliable pre-screen for the identification of chemicals with significant sensitization potential.