Heavy pellets in which the source of selenium was calcium selenate, barium selenate, or elemental selenium have enhanced blood and tissue selenium levels for periods up to 12 months, when dosed singly to sheep grazing pastures of normal selenium status. The components of choice were finely divided metallic iron and elemental selenium possibly in the proportion of 20 : 1.

Typical white muscle disease has been induced in lambs that were normal at weaning but thereafter fed natural dystrophogenic fodder for 2-4 months. Protection from the disease was given by selenium when it was administered regularly as an oral drench, or incorporated into an intraruminal heavy pellet placed in the rumen at weaning.Calcium and magnesium levels in serum were unaffected by the dystrophic condition, although urinary excretion of both ions was decreased. This lowered urinary excretion was associated with high levels of calcium in both heart and skeletal muscle, and to some extent associated with raised levels of calcium and magnesium in washed mitochondria isolated from the same tissues.The respiratory properties of the mitochondria were examined polarographically. No differences were found between heart muscle mitochondria isolated from normal and dystrophic hearts. Skeletal muscle mitochondria from dystrophic animals showed lowered respiratory rates with palmitoyl-DL-carnitine and acetyl-DL-carnitine as substrates. The smaller differences with pyruvate and succinate were not significant. Respiratory control ratios for the dystrophic skeletal muscle organelles were always 1 . 0, but for selenium-supplemented animals were always > 1 ·0.To some extent at least the abnormalities appear to be associated with the high levels of calcium in the tissues and mitochondria of dystrophic lambs.

During the course of an experiment, a "staggers" syndrome developed in Merino ewes which selectively grazed freshly growing Phalaris tuberosa. The symptoms and progress of the disease are described and the toxicity of phalaris is discussed. There was no incidence of staggers amongst 10 ewes which were dosed each week with 7 mg. cobalt, while 11 of 15 untreated ewes were affected, six of them fatally. This response to cobalt is highly significant ( P = 0.00054). In the light of these observations, earlier work relating to "phalaris staggers" is reviewed.

Trace element deficiencies were suspected in cattle in an area of Cape York Peninsula that receives a predominantly summer rainfall of more than 1500 mm and has soils low in nutrient concentration. Consequently cattle were treated with cobalt and copper while grazing Panicum maximum-Stylosanthes guyanensis pastures. After 11 months the fiveweight gains for the four treatment groups were : nil -21 kg ; +Cu -2 kg; +Co +142 kg and +Cu + Co + 121 kg. Many of the animals not given cobalt were emaciated and near death at that time. A group of these animals gained 79 kg in 50 days after receiving supplementary cobalt. Blood copper levels were not affected by treatment but treatment with cobalt decreased blood urea-nitrogen values in the dry season. Cobalt treatment also increased serum vitamin BIZ levels 3-4 fold, increased the liver vitamin B12 levels 10-20 fold and enhanced the storage of copper in the liver. Apart from a short period early in the wet season, the pastures contained less than 0.025 �g Co g-1 dry matter. These levels are discussed in relation to the dietary requirements of grazing cattle.

Trials conducted in South Australia, in an area where pasture improvement by means of the introduction of subterranean clovers has been practised for 10-15 years, have shown a significant improvement in fertility, in ewes treated with selenium. Analysis of all pastures grazed, and of whole blood of stock grazing them, indicated that the selenium status of the feed and of the animals was low. Phyto-oestrogen assays showed the presence of the isoflavones formononetin, genistein, and biochanin A, in the subterranean clover, which was mainly the cultivar Yarloop (Trifolium subterraneum L. var. Yarloop). Administration of selenium four to eight weeks before mating, given either as an oral dose of sodium selenite, or supplied in the form of an intraruminal selenium pellet containing elemental selenium and iron, led to an improvement in fertility; in some cases from 49 to 76 per cent. Also, lamb mortality was reduced by selenium administration to the ewes. There were differences due to selenium administration (P<0.001). Ewe fertility differed between pastures designated 'oestrogenic' and 'non-oestrogenic' (P<0.05). But no interaction between selenium and the presence of phyto-oestrogens could be shown by these experiments. The results are discussed in relation to the problem of infertility associated with the grazing of improved pastures