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Long term experiments were carried out to determine the influence of varying energy intakes on the levels of blood components in lactating beef cows. Lowering the dietary energy intake to 0-95x maintenance produced a fall in bodyweight which continued throughout a 10 week feeding period. There was an initial fall in the plasma glucose level. After four weeks the plasma glucose level began to rise, and at the end of the 10 week period it had almost reached its original level. When bodyweight and plasma glucose were falling cows were infertile, when bodyweight was falling and plasma glucose was rising cows were fertile.

Growth rates and chemical compositions were measured with ram lambs grazing pure stands of perennial ryegrass, timothy, cocksfoot and tall fescue. A group of lambs slaughtered at the start of the trial enabled estimates to be made of the live-weight gains over the summer and the composition of these gains. The composition of the grass was also measured in samples taken at weekly intervals and estimates were made of the nutrients consumed from the different grass plots.The quantities of ash, Ca, P and Mg in the empty bodies of the lambs were within the range of published values from similar studies. They support the contention that grass-fed lambs tend to have larger contents of ash, Ca and P in their empty bodies than concentrate-fed lambs of similar weight. Perennial ryegrass provided a superior diet in that lambs eating this grass grew more quickly, with leaner tissues and higher levels of ash, Ca and P in their empty-body gains. Lambs consuming tall fescue grew most slowly but their mineral contents were as large as the ryegrass-fed lambs when data were adjusted for differences in empty-body weight. Lambs fed on timothy or cocksfoot were the most poorly mineralized in spite of consuming considerably more Ca, P and Mg than the lambs on ryegrass. The data suggest that the efficiencies of absorption of Ca and P in ryegrass may be high, at about 0-64 for Ca and 0-71 for P.

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