Effects of Bull Age on Conception Dates and Pregnancy Rates of Cow Elk
Effects of Bull Age on Conception Dates and Pregnancy Rates of Cow Elk
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公牛年龄对奶牛麋鹿受孕日期和妊娠率的影响
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发表时间：
1996
期刊：
影响因子：
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通讯作者：
J. W. Thomas
中科院分区：
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作者：
J. Noyes;B. Johnson;L. Bryant;Scott L. Findholt;J. W. Thomas
在过去的30年里，俄勒冈州东北部的许多落基山麋鹿（Cervus elaphus nelsoni）种群的奶牛生产力下降了。成熟公牛的数量同时下降，这表明生产力下降的潜在联系。我们评估的影响，公牛年龄的受孕日期和怀孕率的牛麋鹿在一个78平方公里的外壳上的斯塔基实验森林和范围在东北部俄勒冈州从1989年至1993年。我们允许一个单一的公牛队列从1 1/2到5 1/2年成熟，并作为主要的牛群公畜。随后的雄性后代通过狩猎和诱捕减少了数量。我们估计了12月处死的奶牛的受孕日期、妊娠率、身体状况、年龄和泌乳状态。受胎日期随牛龄增加而提前（P = 0.0001），且≤ 2岁和≥ 2岁之间存在显著差异。发情期变得更加同步和缩短71天（n = 26）时，育种是由一岁公牛的41天（n = 33）时，5岁的公牛是主要的父亲。随着牛龄的增加，妊娠率从89%增加到97%，但不显著（P = 0.62）。母牛身体状况最高（P = 0.004），在1989年繁殖时，由一岁公牛。为了提高鹿群的生产力，我们建议设计麋鹿狩猎季节，以便将年龄较大的公牛（≥ 3岁）保留在种群中。
Productivity of cows in many Rocky Mountain elk (Cervus elaphus nelsoni) populations of northeast Oregon has declined over the last 30 years. Numbers of mature bulls declined concurrently, suggesting a potential link that accounts for declining productivity. We evaluated the influence of bull age on conception dates and pregnancy rates of cow elk within a 78-km 2 enclosure on the Starkey Experimental Forest and Range in northeast Oregon from 1989 to 1993. We allowed a single cohort of bulls to mature from 1 1/2 to 5 1/2 years and function as principal herd sires. Subsequent male offspring were reduced in numbers through hunting and trapping. We estimated conception dates, pregnancy rates, body condition, age, and lactation status of cows killed in December. Conception dates occurred earlier as bull age increased (P = 0.0001) and were significantly different between bulls ≤ 2 years and ≥ years of age. The rut became more synchronous and shortened from 71 days (n = 26) when breeding was by yearling bulls to 41 days (n = 33) when 5-year-old bulls were the principal sires. Pregnancy rates increased from 89 to 97% as bull age increased, but not significantly (P = 0.62). Cow body condition was highest (P = 0.004) in 1989 when breeding was by yearling bulls. To enhance herd productivity we recommend that elk hunting seasons be designed so that older bulls ( ≥ 3 yr) are retained in the population.