EFFECT OF ONE CYCLE OF DIVERGENT PHENOTYPIC SELECTION FOR CRUDE PROTEIN, DIGESTIBILITY AND DIGESTIBLE YIELD IN TIMOTHY

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Abstract
A major goal in the breeding of timothy (Phleum pratense L.) is to improve its nutritive value. The objective of this study was to evaluate the effects of one cycle of divergent phenotypic selection for crude protein, digestibility and digestible yield. The progeny of genotypes selected either for high or low crude protein, high or low digestibility, and high or low digestible yield along with a subpopulation representing the unselected original parents were evaluated for dry matter yield and several forage quality characteristics under spaced plant and sward conditions. Under spaced plant conditions significant variation was observed for digestibility (IVDMD), crude protein (CP), acid detergent fiber (ADF) and neutral detergent fiber (NDF). Under sward conditions, significant variation was observed for water retention (WR), ADF and NDF. Under spaced plant conditions, a priori contrasts indicated that one cycle of selection was sufficient to create distinct populations for CP in selecting for CP, for IVDMD and ADF with the IVDMD selection and in 2 out of 3 yr for digestible yield with selection for digestible yield. Evaluation under sward conditions indicated that selection for digestible yield modified CP, WS, ADF, NDF, PV and WR. The results from the evaluation under sward conditions were used to compute different parameters related to potential animal production such as dry matter intake, lactation net energy, energy intake, and different estimates of potential milk production that could be obtained from feeding this hay.Key words: Phleum pratense, timothy, quality, dry matter intake