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The botanical composition, intake and digestibility of the diet consumed by mature lactating and non-lactating cows grazing a native white grass ( Cortaderia pilosa) plant community in the Falkland Islands was measured in four periods between September 1998 and June 1999. Five lactating and five non-lactating cows were used in the summer, autumn and winter; five non-lactating cows were used in the spring. Different cows were used in each period. Plant cuticle patterns in the faeces of cattle were used, in conjunction with the patterns of concentrations of n-alkanes in the faeces, to estimate the botanical composition of the diet and predicted concentrations of C32- and C33-alkanes in the herbage allowed herbage intake and digestibility to be estimated using the n-alkane technique. White grass, sedges and rushes comprised 0·78, 0·64 and 0·63 of the diet in autumn, winter and spring respectively. Fine grasses, smooth-stalked meadow grass ( Poa pratensis L.), annual meadow grass ( Poa annua L.), bent grass ( Agrostis capillaris L.), native fescue ( Festuca magellanica Lam.), Yorkshire fog ( Holcus lanatus L.), wavy hair grass [ Deschampsia flexuosa (L) Trin.] and early hair grass ( Aira praecox L.), were consumed at the expense of sedges and rushes in summer and this coincided with the period of greatest estimated metabolizable energy and crude protein intakes by cows. Lactating cows suffered substantial liveweight loss during autumn and winter and this reflected the low quality of the diet consumed. Phosphorus intakes were insufficient and there was an estimated deficiency of vitamin D in the winter and early spring in cattle that were grazed with the experimental cows. The nutrient restrictions imposed on cattle by the low quality of native pasture during autumn and winter are likely to impair the reproductive potential of breeding females and methods should be investigated to improve the diet consumed by cows during these critical periods if cattle systems are to become sustainable in the Falkland Islands. [ABSTRACT FROM AUTHOR]

The botanical composition, intake and digestibility of the diet consumed by 1-year-old weaner sheep grazing a native white grass plant community in the Falkland Islands was measured in five periods between June 1998 and March 1999. Five different sheep were used in each period. Two methods were used for estimating the botanical composition of the diet: plant cuticle patterns in the faeces of the sheep and the patterns of concentrations of n-alkanes in the faeces of sheep. These methods were used to predict the concentrations of C32- and C33-alkanes in the herbage to allow the estimation of herbage intake and digestibility using the n-alkane technique. It was concluded that the n-alkane technique gave more accurate estimates of diet composition based on the comparison with estimates of nutrient intake derived from liveweight gains of sheep. The dominant pasture species, Cortaderia pilosa, was the predominant species consumed during the cooler periods of the year. In the summer, when the highest liveweight gains of sheep occur, the proportion of fine grass species, including Poa spp., Festuca magellanica and Agrostis capillaris, and herbs and sedges in the diet was highest. Herbage intake was the highest during the summer periods when digestibility was also at its peak. Estimated nutritional deficiencies of metabolizable energy, crude protein, phosphorus and vitamin D3 that limit the growth and development of weaner sheep were evident for up to 9 months of the year. Targeted supplementation regimes that counter specific nutrient deficiencies could be developed on the basis of these results to address critical periods in the growth of young sheep. [ABSTRACT FROM AUTHOR]