Organic selenized yeast enriched with selenoamino acids or inorganic sodium selenate (Na2SeO4) was administered per os three times weekly as a drench for 133 d to previously unsupplemented cows that were grazing low Se pastures. Treatment groups received the equivalent of 2 or 4 mg of Se/d of either supplement form. Control cows did not receive a drench. Samples of blood and milk were collected regularly throughout the trial. Selenium concentrations in blood, milk, casein, and liver and glutathione peroxidase activity in blood and liver are reported as responses per milligram of Se intake. Mean blood Se concentrations in treated cows increased steadily and, by d 133, were 4.7 to 8.8 times that in controls. Selenized yeast was 2 to 3 times more effective than was Na2SeO4, and low Se intakes were 27% more efficient per milligram of Se administered than were high Se intakes at increasing milk Se concentration. Casein Se content mirrored that of milk; among all treated and control cows and throughout the trial, the molar ratio of Se in casein as a percentage of the Se in whole milk was constant at 71 +/- 1.2%. The Se concentration in liver biopsies taken on d 133 was indicative of total Se intake during the trial and ranged from 920 to 3920 nmol of Se/kg of fresh weight. These results demonstrate the differing efficacy of organic and inorganic Se dietary supplements to increase dairy cow Se status and to enhance Se content of milk and casein.

Phosphorus (P) fertilisers are an essential input for the economic production of legume-based pastures in New Zealand (NZ) and Australia, but they often contain some unwanted elements that can contaminate the soil, thereby creating potential risks to the health of grazing animal, food quality, and soil quality. Fluorine (F) and cadmium (Cd) are considered to be the elements of most concern. Incidences of F toxicity (from direct ingestion of fertiliser), and accumulation of Cd in offal products above the maximum permissible concentration (MPC) set by the food authorities, have been reported in NZ. Similarly, Cd concentrations in some food grains may exceed the newly proposed MPCs by the Australian and New Zealand Food Authority. Cadmium and F continue to accumulate in the topsoils of NZ and Australian pastures as a result of P fertiliser use. The mobility of both these elements in soils is low and is similar to that of P. Risk of ground water contamination from F and Cd applied to most NZ pastures is low. The plant uptake of these elements, especially F, is also low in most pastoral soils. Cadmium accumulates mainly in liver and kidney of grazing animals mostly through herbage ingestion, whereas F accumulates mainly in the bones of these animals, mostly through soil ingestion. Soil ingestion is highest during the wetter winter months and at high stocking rates. Models have been developed to assess the impact of fertiliser use on the potential risks associated with F and Cd accumulation in soils. Measures to control F and Cd accumulation in soils, plants, and grazing animals are presented and future research needs are identified.

Sheep prepared either with a rumen cannula, or with a rumen cannula plus re-entrant cannulae in the duodenum and ileum were fed fresh 'Ruanui' perennial ryegrass (R), 'Manawa' short-rotation ryegrass (M) and white clover (C) at dry-matter intakes ranging from 450 to 1000 g/24 h. Paper impregnated with chromic oxide was given once daily via the rumen fistula as a marker.Amounts of Mg, Ca, P, K and Na entering and leaving the small intestine and excreted in the faeces were regressed against the intake of each element for each sheep and these equations (all, other than the faecal excretion of Na, significant (P < 0-05)) were used to calculate the extent of apparent absorption or secretion in the stomach, the small intestine and the large intestine at two levels of OM intake (500 and 800 g daily).Quantities of Mg (at high intake), Ca and K (except sheep fed M) leaving the stomach were significantly lower (P < 0-05), while the amounts of P and Na were significantly higher (P < 0-01) than the amounts consumed. Quantities of Mg (at high intakes) and Ca leaving the small intestine were significantly higher (P < 0-05) while amounts of P, K and Na (at high intakes) were significantly lower (P < 0-05) than the corresponding quantities entering the small intestine. At both intakes in the case of Na and at the higher intakes in the case of the other mineral elements, quantities of Mg, Ca (except sheep fed C), P, K and Na excreted in the faeces were significantly less (P < 0-05) than the amounts entering the large intestine.Thus at the higher intakes there were net absorptions of Mg, Ca and K (except sheep fed M) from, and net secretions of P and Na into, the stomach. The small intestine was the major site of net absorption for P and K and a minor site for Na, while a net secretion of Mg and Ca occurred into this region. Net absorption of Mg, Ca, P, K and Na occurred from the large intestine at the higher intakes.The retention of Mg, Ca and P is discussed in relation to the animals' minimal daily requirements of these elements.

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