名词
中文翻译：牛群放牧指数
同义词：
['cow-calfing index', 'calving index', 'cow-calfing rate']
例句：
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1. The calving index is an important indicator of the health of the herd.
牛群的放牧指数是衡量群体健康状况的重要指标。
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2. The calving index has been declining due to overgrazing.
由于过度放牧，牛群的放牧指数一直在下降。
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3. The calving index is calculated by taking into account the number of cows and calves in a herd.
牛群的放牧指数是通过计算牛群中的母牛和仔牛数量来计算的。