Influence of stage of maturity on the nutritive value of Italian ryegrasses

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Abstract
The influence of harvesting date on the nutritive value of the Italian ryegrass cv. RvP from Belgium and of Bb 1277, an introduced ecotype from the Po valley, was investigated.Ten clonally replicated genotypes of each population were grown as closely spaced plants and two ramets of each genotype harvested every 4 d for a period of 28 d after inflorescence emergence. Dry matter digestibility (DMD) was estimated and fibrosity index (FI) determined on both the leaf and stem fractions, and cellulose and lignin concentrations were determined on the stem fractions.The nutritive value of the leaf in terms of both DMD and FI which was the same for both cv. RvP and Bb 1277 throughout the period of harvesting, was always higher and declined at a slower rate with increasing maturity than that of the stem. The stem of Bb 1277 declined in DMD and increased in FI and cellulose concentration at a significantly slower rate than cv. RvP. Significantly higher levels of DMD were detected in the stem of Bb 1277 for harvests 5 to 8 and significantly lower levels of FI and cellulose concentration from harvests 4 to 8. It was not, however, possible to detect any significant differences in stem lignin concentration. Dry matter yields increased throughout the period of harvesting and there were no significant differences between cv. RvP and Bb 1277.The results are discussed in relation to the breeding potential of the high nutritive value of the Po valley ecotype Bb 1277 and the use of the DMD and FI determinations for selecting for improved herbage quality in Italian ryegrass.

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