It was suggested in our previous works that the silent heat in the cow would be due to deficiency of progesterone or unbalance between estrogen and progesterone levels at the estrous period. Application of synthetic estrogens, as hormonal treatment of the silent heat in the cow, has generally been put in practice in Japan. The purpose of this study is to examine whether progesterone alone or in combination with estrogen is effective on this hormonal disorder.
1. Treatment with progesterone alone.
Four cows diagnosed as to be silent heat by rectal palpation were used in this experiment. They were treated with single injection of progesterone from 5 to 10 mg at the proestrous priod respectively. Results obtained were variable as shown in Table 1. Within the limits of this experiment, it is supposed to be difficult to induce estrous signs on the silent heat cow by progesterone alone owing to conceivable varietes of the unbalance between estrogen and progesterone levels in individual animal.
2.Treatment with progesterone+estrogen.
Sixteen silent heat cows were treated with single injection of 10 mg of progesterone in combination with 5 mg of stilbestrol at the proestrous period. Marked estrous signs were induced from 1 to 5 days (mainly within 3 days) after the injection in 15 (93. 8%) of the treated animals as shown in Table 2. Ovulation took place spontaneously in all of the treated animals. All treated animals were inseminated at the induced estrous period and 10 animals (62. 5%) became pregnant. It was interesting that, in 4 of 5 animals which failed to conceive by the breeding at the induced estrus, marked estrous signs developed in the following estrous cycle without any treatment and pregnancy resulted in 3 of them.
3. Experiment on the ovariectomized cow.
Two ovariectomized cows were used in the estrus inducing experiment involuing injections with progesterone and stilbestrol, either alone or in combination. It was recognized, as shown in Fig. 1, that progesterone+estrogen was more effective to induce natural signs of estrus in the ovariectomized cow than estrogen alone. It was also observed histologically by the endometrial biopsy in one animal that estrous changes in the endometrium were induced more naturally by progesterone+estrogen than by estrogen alone.
It is concluded that the treatment with progesterone in combination with estrogen is more effective to induce estrous signs on the silent heat cow than with estrogen alone.
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