GENETIC-RELATIONSHIPS OF LAMB WEIGHT, MATERNAL ABILITY, AND MATURE EWE WEIGHT IN SWEDISH FINEWOOL SHEEP

Genetic parameters were estimated for weights of lambs from birth to 1 d before slaughter and mature ewe weight (EMW) using REML procedures and single- and two-trait animal models. The data consisted of weight registrations from 5,001 animals descended from 131 sires, 788 dams, 4 8 maternal grandsires, and 530 maternal granddams in an experimental f lock with Swedish finewool sheep. Direct heritabilities increased with lamb age from .07 for birth weight to .21 for weight before slaughter . Maternal heritabilities declined with age from .30 to .07. Direct-ma ternal genetic correlations were positive and increased with age from .11 for birth weight to .73 for weight before slaughter. For daily gai n during shorter periods, direct heritability increased from .07 for t he period from birth until 3 wk of age to .14 for the period from wean ing until 1 d before slaughter. The values for maternal heritabilities were .16 and .03, respectively. The direct-maternal genetic correlati ons ranged from -.11 to .59. The direct heritability for EMW varied be tween analyses from .29 to .63. A nonsignificant maternal heritability of .22 was noted for EMW. Direct genetic correlations between EMW and various lamb weights varied between .36 and .85. Genetic correlations between direct effects on EMW and maternal effects on lamb weights va ried between .39 and .53. Direct and maternal genetic correlations bet ween the lamb weights were positive. The results showed that the mater nal influence on lamb weights decreased with age. It was indicated tha t positive genetic relationships exist between ewe weight and maternal effects on lamb weight. Therefore, selection for larger lamb weights alone will not only increase ewe weights but also improve the maternal ability of the ewe.