Cleveland E R, Johnson R K, Cunningham P J
Dept. of Anim. Sci., University of Nebraska, Lincoln 68583-0908.
J Anim Sci. 1988 Jun;66(6):1371-7. doi: 10.2527/jas1988.6661371x.
Mass selection for an index of increased postweaning average daily gain and decreased backfat thickness was practiced for five generations. Litter size and weight for 221 gilt litters, birth weight and nipple number for 2,242 piglets and weaning weight at 42 d of age for 2,111 pigs were recorded. Carcass measurements were taken on 331 pigs. Differences between means of the lines (select control) were regressed on cumulative selection differential of the index. These regression coefficients were negative (P greater than .10) for total number born, number born alive, number weaned per litter, nipple number and carcass backfat thickness. Coefficients were positive (P greater than .10) for individual pig and litter weights at birth and weaning and for the carcass traits of length, longissimus muscle area and percentage of ham and loin. Absolute values of realized genetic correlations of index with traits evaluated were all .35 or less except the correlation with carcass backfat, which was -.84. None of these was significant; therefore, index selection for lean growth should have little effect on litter size and weight but may have a beneficial effect on carcass backfat.
对断奶后平均日增重增加和背膘厚度降低的指数进行了五代群体选择。记录了221窝后备母猪的窝产仔数和体重、2242头仔猪的出生体重和乳头数以及2111头猪42日龄时的断奶体重。对331头猪进行了胴体测量。品系均值（选择对照）之间的差异根据指数的累积选择差进行回归分析。对于总产仔数、产活仔数、每窝断奶仔猪数、乳头数和胴体背膘厚度，这些回归系数为负（P大于0.10）。对于出生和断奶时的个体猪和窝体重以及胴体性状（长度、背最长肌面积以及火腿和里脊肉百分比），系数为正（P大于0.10）。除了与胴体背膘的相关性为-0.84外，指数与所评估性状的实际遗传相关性绝对值均为0.35或更小。这些均无显著意义；因此，针对瘦肉生长的指数选择对窝产仔数和体重影响不大，但可能对胴体背膘有有益影响。
