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Neutral detergent fiber (NDF) is the most effective and measurable predictor of animal intake. About 70% of the variation in animal production is attributed to differences in intake potential of livestock feed. Sixteen molecular markers associated with NDF in four diver. gently selected smooth bromegrass (Bromus inermis L.) populations were selected from a previous study for further examination for possible use in a marker-assisted selection (MAS) breeding program. The objectives of this experiment were to confirm the association of previously identified markers to NDF concentration in smooth bromegrass populations and to develop a marker-based selection index. Marker and NDF data were analyzed and marker indices were constructed using data from the current and previous studies. Index scores were used to rank genotypes and create selection differentials on the basis of phenotypic data. Marker frequencies calculated on a subpopulation basis between the previous and current studies were highly unrepeatable. Nevertheless, of the 14 groups of marker indices, seven of which accounted for pedigree structure one marker index appears to provide the greatest potential for use in MAS to reduce NDF across all four populations of smooth bromegrass. Where pedigree structure is known, selections made using this index would lead to the largest expected response per year and eliminate the need to collect phenotypic data for as long as linkage relationships remain intact. Where pedigree structure is unknown, a general marker index may be used, or phenotypic data can be utilized along with a marker index. However, inclusion of phenotypic data would necessitate a cost-benefit analysis. [ABSTRACT FROM AUTHOR]

Resources are always limited in plant breeding programs, limiting the number of plots or plants that can be utilized in recurrent selection. Replication of selection units in space or time provides a mechanism to improve the precision of measurements. For smooth bromegrass (Bromus inermis L.), neutral detergent fiber (NDF) is the most effective and measurable predictor of animal intake, a major source of variation for livestock production. The objective of this experiment was to determine the potential benefits and costs of replication in time and space for divergent recurrent selection on NDF of smooth bromegrass. Phenotypic data was used to predict selection response and derive a benefit-cost ratio for a variety of selection criteria based on various numbers of blocks and harvests. Three of the 70 selection criteria examined had an expected selection response significantly greater than that predicted by a log-linear regression of expected selection response as a function of cost. These selection criteria were based on two or three harvests and one or two blocks. Two of the selection criteria, emphasizing one harvest of unreplicated plants, had a benefit-cost ratio significantly above the mean. If financial resources are not a concern, selection based on the mean of multiple harvests in 1 yr results in the highest expected response per year. If financial resources are greatly limited, one harvest of unreplicated plants provides an adequate expected response per cycle but maximizes gain per unit cost. [ABSTRACT FROM AUTHOR]