Effects of potassium fertilizers, age of ewe, and small magnesium supplementation on blood magnesium and calcium levels of lactating ewes

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Abstract
1. An experiment is described which investigated the effects of potassium fertilizer, age of ewe, and a small magnesium supplement, on the plasma magnesium and calcium levels of ewes shortly after lambing.2. Three potassium treatments (0, 1, and 2 cwt. muriate of potash/acre) were used, each being replicated six times, which gave a total of eighteen plots. Each plot was grazed by two old and two young ewes. One ewe of each age in every plot was given supplementary magnesium in the form of two magnesium heavy pellets, which released a total of 150 mg. Mg/day.3. 22% of the ewes had plasma magnesium values below 1·0 mg. Mg/100 ml. on at least one sampling occasion during the experimental period. There was only one clinical case of tetany.4. Neither potassium fertilizer use, nor magnesium supplementation influenced plasma magnesium and calcium levels of the ewes. Old ewes had greater temporary falls in plasma magnesium values and had consistently lower plasma calcium values.5. Attention is drawn to the large individual variation between animals and the consequent need for providing adequate statistical analysis of experiments of this type.