Keeping replacement heifers that were the progeny of primiparous cows mated by artificial insemination, enhances rates of genetic gain. Heifers that were the progeny of primiparous cows were lighter at birth and grew at a slower rate to first calvingcompared with heifers born to muciparous dams. Heifers that were heavier before first calving produced more milk than did lighter heifers. This study aimed to determine if there were liveweight (LWT) or milk-production disadvantages for heifers born fromprimiparous compared with multiparous dams. Data comprised of LWT records from 189,936 New Zealand dairy heifers. Dams were allocated to four groups according to their age: two (2yo; n=13,717), three (3yo; n=39,258), four to eight (4-8yo; n=l20,859) andnine years old or greater (>9yo; n=16,102). Heifers born to 2yo dams were lighter (PO.01) from three to 21 months of age than heifers born to 3yo and 4-8yo dams. The progeny of 2yo and 3yo dams produced similar milksolids yields during their first lactation (304.9±1.6 and 304.1±1.5 kg, respectively), but more (P<0.01) than that of 4-8yo dams (302.4±1.5) and >9yo dams (PO.001; 297.8±1.6 kg). Heifers born to 2yo dams were lighter but produced more milk than heifers from older dams.
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机译：保持替代的小母牛是人工授精配合的初奶牛的后代，提高了遗传增益的率。初步奶牛的后期的小母牛在出生时更轻，并以较慢的速度增长，而第一次加入对山脉的小母牛队的比较。在第一次产犊之前越重的小母牛比较轻的小母牛在生产更多的牛奶。本研究旨在确定与多体水坝相比出生的小母牛的活力（LWT）或牛奶生产缺点。数据包括189,936名新西兰乳品小母牛的LWT记录。根据他们的年龄分配到四组的水坝：两个（2yo; n = 13,717），三（3yo; n = 39,258），四到八（4-8yo; n = l20,859）和Ninne岁或更大（> 9YO; n = 16,102）。出生于2Yo水坝的小母牛从三到21个月的大士开始超过3YO和4-8YO水坝的小母牛。 2YO和3YO水坝的后代在他们的第一次哺乳期间产生了类似的Millsolids产量（分别为304.9±1.6和304.1±1.5公斤），但更多（P <0.01），而不是4-8YO水坝（302.4±1.5）和> 9YO水坝（PO.001; 297.8±1.6千克）。出生于2YO水坝的小母牛较轻，但牛奶比来自旧水坝的小母牛更多。
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