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

L4
MATERIALS AND ìGTHODS
A.
Sources of Data
I. Reproductive traits
The data for 1ítter sLze were obtaíned from the records of the
uníversity of Manitoba swine breeding project over the períod of years
1967 to L977 at the Glenlea Research Station. First parity gilts of the
Managra breed r^iere included in this study. Managra r¡ere developed
from a gene pool consisting of about 457á Swedish Landrace , 2O7. I^Iessex
Saddleback, 15% I,Ielsh ar'ð 707. Minnesota //l-Berkshire-Yorkshire-Tarff^rorth.
Table 3 illustrates
the pattern of development of the Managra and the
current farrowing groups (Parker, f977).
Parents of each generation consisted of 20 to 30 boars and 90 to
120 gilts. Selection of parents based on backfat thickness as measured
by adjusted live ultrasonic probe, adjr,rsted age to 90 kg live weight and
physical soundness. There \¡ras no line crossing among the groups and inbreedíng
was rulnimized each generation. LitËers from which fewer than
3 pigs \47ere weaned were not included in the study. The number of liËters
which contributed to this study from the diffeïent groups in the different
years are lísted ín Table 4. Total number of pigs born, total
number of pigs born alive, total number of pÍgs weaned, average bÍrth
weight and average weaning weight were the five reproductive traits
examined. Average birth weight and average weaning r^reight were adjusted
for number born alive and number weaned, respectlvely.
The adjustments
were used only rvhen calculating phenotypic means. The equation for
adjustmenË (Huntsberger, L977) was: