Bennett Gary L, Thallman Richard M, Snelling Warren M, Keele John W, Freetly Harvey C, Kuehn Larry A
USDA, Agricultural Research Service, U.S. Meat Animal Research Center, Clay Center, NE.
Transl Anim Sci. 2021 Jan 27;5(1):txab009. doi: 10.1093/tas/txab009. eCollection 2021 Jan.
One approach to reducing calving difficulty is to select heifers with higher breeding value for calving ease. Calving ease is often associated with lower birth weight and that may result in other possible effects on lifetime productivity. Females from experimental select and control calving ease lines within each of the seven populations were compared. Random samples of 720 heifers from lines selected for better calving ease breeding values and 190 heifers from control lines selected for average birth weights were followed through four parities. Select and control lines within the same population were selected to achieve similar yearling weight breeding values. Weights of sampled heifers in select lines were 2.6 kg ( < 0.01) lighter at birth but not different from control lines at weaning. Select lines had significantly shorter hip height, lighter mature weight, and greater calving success at second parity. Their calves were born significantly earlier with lighter weights and less assistance. Significant interactions with parity showed fewer calves assisted and greater calf survival to weaning as heifers but negligible differences with control lines in later parities. Steer progeny sampled from these dams in select lines ( = 204) were not different from steers in control lines ( = 91) for hot carcass weight but had significantly greater fat depth. Two production systems were compared considering the seven populations as replicates. The systems differed in selection history of females (select and control lines) and the use of bulls within their lines as young cows, but used the same bulls in both lines as older cows. Cows were culled after single unsuccessful breeding and kept for up to four parities. Select line cows tended ( ≤ 0.10) to wean more calves and stay in the herd longer. They were assisted significantly fewer times at calving and had greater calf weight gain to weaning when evaluated over their herd life. Mature weights were lighter in select lines, but marketable cow weight from the systems was nearly identical. Control lines did have more marketable young cow weight and select lines older cow weight. Weaned calf weight per heifer starting the system was significantly greater for the select heifer system due to greater survival of calves from heifers and greater calving success at second parity. No important unfavorable effects of genetic differences in calving ease were identified in this experiment.
降低产犊难度的一种方法是选择产犊容易度育种值更高的小母牛。产犊容易度通常与较低的出生体重相关，这可能会对终生生产力产生其他可能的影响。对七个种群中每个种群内实验性选择的产犊容易度品系和对照产犊容易度品系的雌性进行了比较。从为更好的产犊容易度育种值而选择的品系中随机抽取720头小母牛样本，从为平均出生体重而选择的对照品系中随机抽取190头小母牛样本，跟踪记录它们四个胎次的情况。选择同一种群内的选择品系和对照品系，以实现相似的周岁体重育种值。选择品系中抽样小母牛的出生体重轻2.6千克（P<0.01），但断奶时与对照品系无差异。选择品系的臀高显著更短，成熟体重更轻，第二胎次的产犊成功率更高。它们的犊牛出生显著更早，体重更轻，所需助产更少。与胎次的显著交互作用表明，作为小母牛时，选择品系得到助产的犊牛更少，断奶时犊牛的存活率更高，但在后续胎次中与对照品系的差异可忽略不计。从这些选择品系的母畜中抽样的阉牛后代（n = 204）与对照品系的阉牛（n = 91）相比，热胴体重没有差异，但脂肪厚度显著更大。将这七个种群视为重复，比较了两种生产系统。这两种系统在雌性的选择历史（选择品系和对照品系）以及作为年轻母牛时品系内公牛的使用方面有所不同，但作为年长母牛时，两个品系使用相同的公牛。母牛在单次配种未成功后被淘汰，最多饲养四个胎次。选择品系的母牛倾向于（P≤0.10）断奶更多的犊牛，在牛群中停留的时间更长。在产犊时，它们得到助产的次数显著更少，在其整个牛群生活期间评估时，犊牛到断奶时的体重增加更大。选择品系的成熟体重更轻，但两种系统的可上市母牛体重几乎相同。对照品系的可上市年轻母牛体重更多，选择品系的可上市年长母牛体重更多。由于选择品系的小母牛所产犊牛的存活率更高以及第二胎次的产犊成功率更高，选择品系小母牛系统中每头开始该系统的小母牛的断奶犊牛体重显著更高。在本实验中未发现产犊容易度基因差异的重要不利影响。
