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The present study was carried out to clarify the time of recurrence of estrus after parturition in Japanese Shorthorn cows. A total of fifty-one Japanese Shorthorn cows were used in this experiment. Their average ages (years), calving numbers and body weight (kg) were 7±3 (Mean±SD), 5±3 and 468±63 respectively. They were on pasture from May through December and raised with loose barn method from December through next May. Calving started in March and ended in May. Involution of the uterus was examined by the rectal palpation, and estrus was mainly checked by standing estrus. Plasma progesterone was determined by the radioimmunoassay. Forty-three Japanese Black cows fed under the similar conditions were used as controls. The results obtained were as follows:<BR>1. Days required for involution of uterus after parturition ranged from 21 to 57 days with a mean of 32±8 days in the Japanese Shorthorn cows and ranged from 20 to 61 days with a mean of 35±8 days in the Japanese Black cows. There was no significant difference between the two breeds.<BR>2. Days required for reccurence of estrus after parturition ranged from 24 to 106 days with a mean of 57±19 days in the Japanese Shorthorn cows and ranged from 24 to 74 days with a mean of 44±14 days in the Japanese Black cows. There was a significant difference between the two breeds (P<O.01).<BR>3. The variations in levels of plasma progesterone after parturition in seven Japanese Shorthorn cows were as follows. In four cows the levels of plasma progesterone were less than 1ng/m<I>l</I> during 60 days post partum and notable variations were not detected. In the remaining three cows the plas-ma progesterone increased transiently on day 56 (3.2ng/m<I>l</I>), day 61 (3.7ng/m<I>l</I>) and day 63 (5.4ng/m<I>l</I>) post partum.<BR>The results suggest that the time required for the post partum recurrence of estrus with external symptom is at least 60 days in the most Japanese Shorthorn cows.
- 日本繁殖生物学会の論文
日本繁殖生物学会 | 論文
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