Performance of Lambs on Perennial Ryegrass, Smooth Bromegrass, Orchardgrass and Tall Fescue Pastures II. Mineral Utilization, in Vitro Digestibility and Chemical Composition of Herbage2

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Abstract
Mineral balance trials with lambs fed perennial ryegrass, smooth bromegrass, orchardgrass and tall fescue herbage at two growth stages in 2 years showed significant effects of date of cutting and grass species on the concentration, apparent absorption (AA) and retention of major elements. Concentrations of calcium, phosphorus, potassium and sulfur declined with maturity, with little change in magnesium. Mean AA values for calcium, phosphorus, magnesium, potassium and sulfur were 29.4, 10.4, 36.6, 89.2 and 64.7%, respectively. Apparent absorption of calcium, phosphorus, potassium and sulfur declined with maturation of the herbage, while magnesium availability increased. Species differences in AA and retention of minerals were noted, although between-animal variability was high. Lambs on tall fescue utilized calcium, phosphorus, and magnesium less efficiently, although concentrations of these elements in fescue were as high or higher than in the other species. Calculations of requirements indicated that concentrations of calcium, phosphorus and magnesium in herbage may have been inadequate for maximum growth of early weaned lambs. Seasonal changes in the in vitro dry matter digestibility (IVDMD) and chemical composition of grazed pastures were determined, and relationships between chemical composition, mineral utilization and in vivo DMD and intake were examined by multiple regression analysis. Lignin was found to be the most important component affecting IVDMD. When measures of mineral concentration and availability were included in regressions of composition on nutritive quality of the grasses, they were found to improve significantly the proportion of variability in DMD and intake accounted for by structural organic fractions of the herbage. Phosphorus concentration and availability were found to have a significant effect on the level of intake of harvested grass by growing lambs. Copyright © 1978. American Society of Animal Science . Copyright 1978 by American Society of Animal Science.

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