USDA, ARS, Roman L. Hruska U.S. Meat Animal Research Center, PO Box 166, Clay Center, NE 68933, USA.
J Anim Sci. 2013 Sep;91(9):4486-91. doi: 10.2527/jas.2013-6465. Epub 2013 Jul 3.
Longevity and lifetime productivity are important factors influencing profitability for the cow-calf producer. Heifers that conceive earlier in the breeding season will calve earlier in the calving season and have a longer interval to rebreeding. Calves born earlier in the calving season will also be older and heavier at weaning. Longevity data were collected on 2,195 heifers from producers in South Dakota Integrated Resource Management groups. Longevity and weaning weight data were collected on 16,549 individual heifers at the U.S. Meat Animal Research Center (USMARC). Data were limited to heifers that conceived during their first breeding season. Heifers were grouped into 21-d calving periods. Heifers were determined to have left the herd when they were diagnosed not pregnant at the end of the breeding season. Heifers that left the herd for reasons other than reproductive failure were censored from the data. Heifers that calved with their first calf during the first 21-d period of the calving season had increased (P < 0.01) longevity compared with heifers that calved in the second 21-d period, or later. Average longevity for South Dakota heifers that calved in the first or later period was 5.1 ± 0.1 and 3.9 ± 0.1 yr, respectively. Average longevity for USMARC heifers that calved in the first, second, or third period was 8.2 ± 0.3, 7.6 ± 0.5, and 7.2 ± 0.1 yr, respectively. Calving period as a heifer influenced (P < 0.01) unadjusted weaning BW of the first 6 calves. Estimated postpartum interval to conception as a 2-yr-old cow was greater for females that calved in the first period as heifers but did not differ between heifer calving periods in subsequent calving seasons. In summary, heifers that calved early in the calving season with their first calf had increased longevity and kilograms weaned, compared with heifers that calved later in the calving season.
寿命和终生生产力是影响奶牛养殖者盈利能力的重要因素。在繁殖季节较早怀孕的小母牛将更早地在产犊季节产犊，并具有更长的再繁殖间隔。在产犊季节较早出生的小牛也会更老、更重。2195 头小母牛的寿命数据来自南达科他州综合资源管理小组的生产者。16549 头小母牛的寿命和断奶体重数据来自美国肉类动物研究中心（USMARC）。数据仅限于在其第一个繁殖季节怀孕的小母牛。小母牛被分为 21 天的产犊期。当繁殖季节结束时，小母牛被诊断未怀孕时，它们就被认为已经离开牛群。由于繁殖失败以外的其他原因离开牛群的小母牛被从数据中剔除。在产犊季节的前 21 天内产下第一头小牛的小母牛与在第二 21 天或更晚产犊的小母牛相比，寿命更长（P < 0.01）。在产犊季节的第一期或以后产犊的南达科他州小母牛的平均寿命分别为 5.1 ± 0.1 和 3.9 ± 0.1 年。在产犊季节的第一期、第二期或第三期产犊的 USMARC 小母牛的平均寿命分别为 8.2 ± 0.3、7.6 ± 0.5 和 7.2 ± 0.1 年。作为小母牛的产犊期影响（P < 0.01）前 6 头小牛的未经调整的断奶 BW。作为 2 岁母牛的产后间隔到受孕估计值在第一期产犊的雌性中更大，但在随后的产犊季节中，小母牛的产犊期之间没有差异。总之，与在产犊季节较晚产犊的小母牛相比，在产犊季节较早产犊的小母牛的第一头小牛的寿命和断奶体重增加。
