Metabolism trials were conducted with sheep to study the effects of conservation of herbage as silage, frozen or artificially dried grass upon the magnesium and calcium availabilities in the conserved products.When the diet was changed, approximately isomagnesaemically, from hay and barley to each of the conserved products, there was a highly significant (P < 0-001) decrease in the plasma magnesium concentration. However, the plasma magnesium concentrations of the ewes eating the artificially dried grass were significantly lower (P < 0-05) than the corresponding values when they ate the frozen grass or silage. No changes were seen in the plasma calcium concentrations.The apparent availability of magnesium in the silage was significantly higher (P < 0-05) than that in the frozen and artificially dried grasses. Also, the apparent availability of magnesium and calcium was lower in the dried grass than in the other two products, whilst the retention of both magnesium and calcium was significantly lower (P < 0-05) when the dried grass was eaten as compared with the frozen grass and silage. The percentage urinary loss of magnesium was greatest on the silage and least on the dried-grass diet.It was concluded that artificially drying grass caused a reduction in magnesium availability.
SUMMARYA balance experiment was carried out using four young lactating goats in a Latin square design, fed with perennial ryegrass (Lolium perenne) from plots that had received 377 kg K/ha (diet 1); 63 kg K plus 377 kg Na/ha (diet 2); 188 kg K plus 188 kg Na/ha (diet 3) or no fertilizer (control diet 4).The apparent availability of Mg was high in all the grass diets (0·355–0·469); it was significantly depressed (P < 0·05) when the intake of K was high (diet 1); but was not significantly different when a high intake of K was accompanied by a high intake of Na (diet 3).There was a significantly lower (P < 0·05) apparent availability of Na in diet 4 and a significantly higher (P < 0·05) apparent availability of K in diet 3. There were no significant differences in the apparent availability of Ca.The plasma Mg concentration was not significantly affected by any dietary treatment but did decrease temporarily when diets were changed.There were no significant effects on mineral concentrations in the milk.
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