Estimation of genetic and phenotypic parameters in a closed ...

LITERATURE REVIEI^]
A.
Reproductive Traits
I. Heritability EstÍmates
It has been well recognLzed that characters closely related to
reproductive fitness have low heritability
estimates. Some of the heritability
estimates reported by differenË workers are listed in Table 1.
Heritability estimates from the literature range from -0.03 to 0.11,
-0.01 to 0.28, 0.04 to 0.29, -0.04 ro 0.27 ar'ð.0.02 ro 0.46 for roral
number of pigs born, number of pigs born alive, number of pigs weaned,
average birth weight and average weaning weight, respectívely.
An
exception to the above range has been reported by young et al. (1978)
from an analysis of data rlom 2,095 gilts. These workers reported high
heritabílities of 0.72!0.22 and 0.66!0.23, for total number of pigs born
and ni¡nber of pigs born alive, respectively. young et al. (197S) cited
that Po¡ofrey et al. (L975) utilized six seasons of data instead of eight
from the sane population and reported heritabilitíes
of 0.0910.08 and
0 .0910.09 f or these trrTo traíts .
Revelle and Robison (1973) examined data from 1,078 two-generation
and 710'three-generation pedigrees to find the causes of 1ow heritabilities
of reproductive traits. The gilts were dívided into three
groups as high (78"/"), nr-iddle (647") and 1ow (r9i() based on rhe firsË
generation litter size. The daughterrs litter size of the 1ow group exceeded
the high and the niddle groups. The results suggested a negative
environmental correlation between the litter
size of dam and daughter.
Heritabilíty estinates for litter size at birth were 0.13t0.06 from the
regression of daughter on dam and 0.2810.26 from the regression of