Effects of Female Sex Hormones and Dietary Magnesium Levels in Sheep

The major objectives of this study were to evaluate (a) the effects of diet on magnesium, calcium and potassium metabolism in yearling wethers and (b) the effects of progesterone, estradiol and diethylstilbestrol (DES) on the metabolism of the minerals.

A two by two factorial design was selected whereby twelve yearling crossbred wether lambs were divided into four groups of three. One group was fed a basal diet plus magnesium along with hormones, one group was fed a basal diet plus magnesium without hormones, one group was fed a magnesium-deficient diet along with hormones, and one group was fed a magnesium-deficient diet without hormones.

During trial one, two of the groups were injected intramuscularly with progesterone every twelve hours for four consecutive days. Then, forty-eight hours after the last injection of progesterone, 100 μg of estradiol was injected intramuscularly in two separate injections (50 μg per injection) six hours apart. This was intended to simulate the hormonal milieu of an ewe coming into estrus. At the time of the initial injection of estradiol, 61.3 μc of magnesium-28 and 701 μc of calcium-45 were administered orally via a lubricated balling gun to each of the wethers. Whereas during trial two, four mg DES was administered orally for twenty-one days while consuming either the basal diet plus magnesium or a magnesium-deficient diet.

The major finding of this research was that when animals were fed a magnesium-deficient diet along with a high-potassium level in the diet there was a greater retention of potassium than in animals fed a basal diet plus magnesium and a high level of potassium.

The progesterone and estradiol stimulated appetite, increased calcium and magnesium intake, increased calcium and magnesium excretion in the urine and feces, increased retention of potassium, increased plasma potassium, decreased plasma calcium, increased the calcium-45 in urine and increased the calcium-45 in the plasma at peak levels (p < 0.05). The interaction of these two hormones with diet showed that the animals that were fed the basal diet plus magnesium and injected with hormones excreted more magnesium-28 for the twenty-four and forty-eight hour test period, and for the complete test period.

The animals fed DES consumed less feed, consumed less calcium and magnesium, excreted less calcium and magnesium in the feces, excreted more magnesium in the urine, and excreted less calcium in the urine and had a greater concentration of magnesium in the plasma. The interaction of DES X diet showed that the animals that were fed DES and maintained on a magnesium-deficient diet had the least amount of plasma potassium of any group.