Genetic and phenotypic parameters for dietary selection of mountain big sagebrush (\u3ci\u3eArtemisia tridentata\u3c/i\u3e Nutt. ssp. \u3ci\u3evaseyana\u3c/i\u3e [Rydb] Beetle) in Rambouillet sheep

The heritability of diet selection for mountain big sagebrush (Artemisia tridentata Nutt. ssp. vaseyana [Rydb] Beetle) by grazing sheep was estimated from fecal samples collected from 549 Rambouillet ewes. Fecal samples were collected in September and October during 1996 and 1997 from free-grazing ewes on intermountain sagebrush-bunchgrass rangelands at the U.S. Sheep Experiment Station in Idaho. The total number of fecal samples was 1,949. Fecal samples were evaluated for composition of big sagebrush by near-infrared spectroscopy. Percentage of sagebrush in the diet was less in September than in October (21.6 vs 31.7%, respectively). Single-trait and bivariate derivative-free REML analyses were per-formed to genetically compare percentage of sagebrush in the diet in September and October. Heritability estimates were similar between September and October measurements (0.25 and 0.28, respectively). The genetic correlation between September and October percentages of sagebrush in the diet was high (0.91), implying that there is strong genetic similarity between September and October measurements and that an annual measurement may be sufficient for selection. These results contribute to a greater understanding of dietary preferences in freely grazing sheep, and suggest opportunities to improve production efficiency and forage management through selection for dietary preferences