Classifying sheep grazing environments using satellite data to quantify genotype by environment interactions

Australian sheep grazing environments are currently classified into 3 very broad zones (High Rainfall, Wheat/Sheep and Pastoral) that do not differentiate sheep grazing environments to a level allowing sheep producers to assess the impact grazing environments may have on sire progeny performance. If a genotype by environment interaction (GEI) is expressed more as environments diverge then a finer classification of environments may help breeders when selecting stud rams. A sheep grazing environment classification system has been developed in this study using readily obtainable monthly Normalised Difference Vegetation Index (NDVI), from satellite data, and monthly maximum temperature for a 10 year period. Cluster analysis was used on the NVDI and temperature data to create 25 sheep grazing environment classes (SGEclass) around Australia. Two-way analysis of variance revealed a significant interaction between sire progeny performance and SGEclass for hogget weight, fibre diameter and greasy fleece weight. Further ASReml analysis of Merino data from Sheep Genetics illustrated that sire by SGEclass explained similar amounts of variation as sire by flock. Recording the geographic location of the flock would improve the ability to account for environmental differences between flocks.