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第三十三卷(2004)
乳牛一年一胎的頻率
吳明哲 張菊犁 陳志毅 李素珍 曾青雲 黃鈺嘉 李世昌
行政院農業委員會畜產試驗所
台灣乳牛群改良計劃於近10年間(1995–2004)，每胎泌乳天數平均分別為346(n=9491頭)、351(9991)、352(9435)、350(9962)、360(13709)、347(14891)、342(15301)、348(17493)、356(20051)、352(12747)天；乾乳年齡平均分別為5.21、5.29、5.29、5.33、5.25、5.22、5.17、5.09、5.06、5.11年；各年度的泌乳天數平均達350天之久，暗示要一年一胎的的機會不高。不過，具完整系譜3760頭經產牛於2003年11月至2004年4月間分娩，胎距平均最少的第一名330天、前100名的337天，平均胎距為450天；顯示仍有2%以上(100/3760)的乳牛可由胎距450天縮短為337天，具有一年一胎的能力。胎距平均前100名的經產牛有4胎以上(包括4胎)的頭數有22%，也有一頭(ID10016417；29H4397公牛的女兒牛)是10胎，胎距平均為335天。利用近七年的分娩資料，把五歲齡之前就有三胎記錄的經產牛14,866頭，計算個別牛的胎距並由少至多排序，胎距平均為365天以內的牛頭數佔27.4%(4074/14866)。乳牛繁殖的六大地區，年產一胎的頻率在彰化為36.0%(1041/2889)、台南為24.1%(680/2821)、屏東為12.6%(269/2138)、嘉義為30.5%(649/2131)、雲林為 19.9%(316/1586)、高雄為30.6%(299/976)。再看2002至2004年這三年的上半年，一至六月的分娩頭數比例，每年的三月份是最多的，三月份分娩頭數比例已由2002年的20.9%及2003年的20.3% 增加為2004年的27.4%；每年的五月份泌乳牛的305-2X-ME乳量預估值平均分別有6903、7085和7107公斤。因此，乳牛在三月分娩可能有利於泌乳天數的縮短為305天及其胎距在365天左右，藉以達到乳牛一年一胎的繁殖方式。
關鍵語：乳牛、胎距、泌乳天數。
FREQUENCY OF ONE CALVING PER YEAR IN DAIRY COWS
M. C. Wu, C. L. Chang, J. Y. Chen, S. J. Lee, C. Y. Tseng, Y. C. Huang and S. C. Lee
Livestock Research Institute, Council of Agriculture, Executive Yuan
Lactation length of milking cows in the Dairy Herd Improvement Program from 1995 to 2004 were 346(n=9491 cows), 351(9991), 352(9435), 350(9962), 360(13709), 347(14891), 342(15301), 348(17493), 356(20051) and 352(12747) days, respectively. Mean age of drying for milking from 1995 to 2004 were 5.21, 5.29, 5.29, 5.33, 5.25, 5.22, 5.17, 5.09, 5.06 and 5.11 years old, respectively. Most of means on lactation length in years were more than 350 days; therefore, the possibility to having one calving per year would be less. However, the top first rank cow had 330 days of calving interval as compared from 3760 cows which giving birth during the period between November of 2003 and April of 2004 with their pedigree data. The 100th cow of top listings had 337 days of calving interval, which that there were more than 2%(100/3760) of cows having the ability to having one calving per year as compared to the mean of 450 days on calving interval in the population. There were 22% of cows had four and more lactations in the top 100 cows with the shortest calving interval. Cow ID 10016147, daughter of 29H4397 bull, had a mean of 335 days on her 10 lactations. A total of 14,866 cow having three lactations within five year olds dated from 1997 to 2004 and mean of calving interval of each cow was calculated and ranked in ascending order. There were 27.4%(4074/14866) of cows with calving interval less than 365 days. In the greater six county region of cow herds, frequencies of one calving per year was 36.0%(1041/2889) in Chunghua, 24.1%(680/2821) in Tainan, 12.6%(269/2138) in Pingtung, 30.5%(649/2131) in Chiayi, 19.9%(316/1586) in Yulin, and 30.6%(299/976) in Kaohsiung. Month ratio for calving among January to June were calculated and it showed that March was the highest and was 20.9% in 2002, 20.3% in 2003 and 27.4% in 2004 with growth. Milk yield of 305-2X-ME were 6903, 7085 and 7107 kg, respectively, for milking cows in May of 2002 to 2004. Hence, cows gave birth in March not only to shorten lactation length to 305 days but also to maintain a 365-day of calving interval and such reproduction way would easily to have the status of one calving per year in Taiwan.
Key Words: Dairy cows, Calving interval, Lactation length.
  
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