Characterisation of terminal sire sheep farm systems, based on a range of environmental factors: a case study in the context of genotype by environment interactions using Charollais lambs.

The objective of this study was to define different terminal sire flock environments, based on a range of environmental factors, and then investigate the presence of genotype by environment interactions (G×E) between the environments identified. Data from 79 different terminal sire flocks (40 Texel, 21 Charollais and 18 Suffolk), were analysed using principal coordinate and non-hierarchical cluster analyses, the results of which identified three distinct environmental cluster groups. The type of grazing, climatic conditions and the use of vitamins and mineral supplements were found to be the most important factors in the clustering of flocks. The presence of G×E was then investigated using data from the Charollais flocks only. Performance data were collected for 12 181 lambs, between 1990 and 2010, sired by 515 different sires. Fifty six of the sires had offspring in at least two of the three different cluster groups and pedigree information was available for a total of 161 431 animals. Traits studied were the 21-week old weight (21WT), ultrasound muscle depth (UMD) and log transformed backfat depth (LogUFD). Heritabilities estimated for each cluster, for each trait, ranged from 0.32 to 0.45. Genetic correlations estimated between Cluster 1 and Cluster 2 were all found to be significantly lower than unity, indicating the presence of G×E. They were 0.31 (±0.17), 0.68 (±0.14) and 0.18 (±0.21) for 21WT, UMD and LogUFD, respectively. Evidence of sires re-ranking across clusters was also observed. Providing a suitable strategy can be identified, there is potential for the optimisation of future breeding programmes, by taking into account the G×E observed. This would enable farmers to identify and select animals with an increased knowledge as to how they will perform in their specific farm environment thus reducing any unexpected differences in performance.

Three dimensional analysis of the lamina cribrosa in glaucoma.

BACKGROUND/AIM: Structural changes in the lamina cribrosa have been implicated in the pathogenesis of glaucomatous optic atrophy. The aim of this study was to determine a measure the surface variability of the cup floor in normal subjects and patients with glaucoma. METHODS: A sample of age matched normal subjects (NN), patients with low tension glaucoma (LTG), and primary open angle glaucoma (POAG) were included in the study. The glaucoma groups were matched for the severity of the visual field loss. Mean 10 degree topographic images of normal and glaucomatous eyes from the Heidelberg retina tomograph were imported into ERDAS image processing software where topographic analysis of the cup floor could be assessed. Each image was processed using customised spatial filters that calculated the surface depth variation in localised neighbourhood areas across each image. The local change in depth across the cup floor surface was determined and compared between the three clinical groups. RESULTS: The depth variation in the cup floor was largest in normal subjects followed by LTG and POAG. Highly statistically significant differences in surface depth variability of the cup floor existed between normal and LTG (p = 0.005), between normal and POAG (p<0.0001), and between LTG and POAG groups (p<0.0001). The variability and skewness of depth difference across the optic cup floor were also significantly different between the three clinical groups. CONCLUSION: A new parameter quantifying depth variations in the cup floor significantly discriminated between groups of normal and glaucoma patients. This new parameter may contribute to a better understanding of the pathogenesis of the glaucomatous optic nerve damage in different types of glaucoma.

Measurement of a novel optic disc topographic parameter, "spikiness", in glaucoma.

BACKGROUND: Structural changes in the lamina cribrosa have been implicated in the pathogenesis of glaucomatous optic atrophy, but not observed. This paper presents a novel parameter of topographic variability within the optic disc, termed "spikiness", which may reflect glaucoma-related changes in the lamina. METHODS: Four age-matched groups of normal patients (n=12, mean age 64.8 years) and patients with ocular hypertension (n=14, mean age 63.1), primary open-angle glaucoma (n=11, mean age 70) and low-tension glaucoma (n=15, mean age 66.3) were recruited. Images of normal and glaucomatous eyes from the Heidelberg Retina Tomograph were imported into ERDAS image processing software where the spikiness data (30 consecutive mean surface height values across the base of the optic cup in both the vertical and horizontal meridians) were extracted in a format that facilitated further statistical analysis. RESULTS: Significant differences in topographic variability (spikiness) existed in the vertical (F=3.64, P=0.01) but not the horizontal meridian (F=1.25, P=0.3) through the optic disc. Spikiness was inversely related to Humphrey mean deviation (P<0.05), and cup-disc ratio (P<0.004) and was directly related to nerve fibre layer thickness (P<0.005). Of particular interest was the finding that the spikiness measure was the only optic disc parameter to significantly discriminate low tension glaucoma from primary open angle glaucoma. CONCLUSION: A new measure of surface variability (topography) at the floor of the optic cup has been described. The new index of spikiness may represent a measurement of lamina cribrosa fragility which has been implicated, but not previously estimated, in glaucomatous eyes.