Nielsen M K, Freking B A, Jones L D, Nelson S M, Vorderstrasse T L, Hussey B A
University of Nebraska-Lincoln 68583-0908.
J Anim Sci. 1997 Jun;75(6):1469-76. doi: 10.2527/1997.7561469x.
Divergent selection for heat loss (kcal.kg-.75.d-1), measured in 9- to 11-wk-old male mice, was conducted for 15 generations. Selection for high (MH) and low (ML) heat loss and unselected control (MC) occurred in each of three replicates for a total of nine unique lines. Feed intake in males was measured during Generations 9 through 15. Body mass at commencement of mating in females and at time of measurement of heat loss in males was recorded. Body fat percentage at 12 wk for animals of Generations 6, 10, and 14 was predicted as a function of electrical conductivity and body mass. Litter size was recorded for all generations, and components of litter size were evaluated at Generation 11 in one replicate and Generation 12 in the other two replicates. Feed intake changed in the same direction as heat loss for the MH and ML selections; at Generation 15, the difference between MH and ML (P < .002) was 20.6% of the MC mean. Body mass did not change with selection for heat loss. Differences in body fat percentage were not significant in earlier generations, but at Generation 14, MH and ML were significantly (P < .01) different with MH mice having the lowest fat percentage; MC was intermediate. Selection had a significant (MH vs ML; P < .01) effect on litter size, causing an increase in MH and a decrease in ML. This difference was explained by a difference (P < .01) in ovulation rate. There was no asymmetry of response in feed intake, fatness, litter size, or number of ovulations.
对9至11周龄雄性小鼠的热量散失（千卡·千克^-0.75·天^-1）进行了15代的分化选择。在三个重复组中分别进行高（MH）热量散失、低（ML）热量散失选择以及未选择的对照（MC），共形成九条独特品系。在第9代至第15代期间测量了雄性小鼠的采食量。记录了雌性小鼠开始交配时的体重以及雄性小鼠测量热量散失时的体重。根据电导率和体重预测了第6代、第10代和第14代动物12周龄时的体脂百分比。记录了所有世代的窝仔数，并在一个重复组的第11代和另外两个重复组的第12代评估了窝仔数的组成部分。对于MH和ML选择，采食量的变化方向与热量散失相同；在第15代时，MH和ML之间的差异（P <.002）为MC平均值的20.6%。体重并未随着热量散失选择而改变。在早期世代，体脂百分比差异不显著，但在第14代时，MH和ML存在显著差异（P <.01），MH小鼠的体脂百分比最低；MC处于中间水平。选择对窝仔数有显著影响（MH与ML相比；P <.01），导致MH增加而ML减少。这种差异可以通过排卵率的差异（P <.01）来解释。在采食量、肥胖程度、窝仔数或排卵数方面不存在反应不对称性。
