Concentration and availability to sheep of N, P, K, Ca, Mg and Na in chickweed, dandelion, dock, ribwort and spurrey, compared with perennial ryegrass

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Abstract
SUMMARY: The concentrations of water-soluble carbohydrate, N, nitrate-N, P, K, Ca, Mg and Na were determined in six plant species: chickweed (Stellaria media (L.) Vill.), dandelion (Taraxacum officinale Weber), dock (Rumex obtusifolius L.), ribwort (Plantago lanceolata L.), spurrey (Spergula arvensis L.) and perennial ryegrass (Lolium perenne L.). Field crops of these species were grown at Aberystwyth in 1985,1986 and 1987. In 1985 and 1986 the rumen contents and faeces of lambs fed artificially dried diets of the different species were analysed for N, P, K, Ca, Mg and Na. The intake, apparent availability and, in 1986, retention of each element by the lambs on each diet were calculated.The results illustrate the potential of dicotyledonous species to extend the range of concentration of some major elements beyond that normally found in temperate grasses. Chickweed was particularly high in P and K, dandelion in K and Mg, dock in Mg, ribwort in Ca and spurrey in Mg and Na. The apparent availability of the elements studied was as high in chickweed, dandelion and spurrey as in ryegrass. The apparent availability of N and P was lower in dock and ribwort than in ryegrass, possibly due to heat damage during drying. All five dicotyledonous species had a higher Mg concentration in herbage than ryegrass (c. 70% higher, on average) and all led to a higher Mg concentration in rumen contents than ryegrass (c. 70% higher, on average). Retention of Mg was three times as great, on average, in sheep fed dicotyledonous diets as in sheep fed ryegrass. The concentration of water-soluble carbohydrate was lower in the dicotyledonous species than in ryegrass. The concentration of nitrate-N was rather high in ribwort when harvested at a leafy stage in October. Dock was moderately low in nitrate-N, despite a rather high concentration of total N.