- An experiment was conducted to determine if selection from
standardized litters would be effective in separating lines of mice
selected for increased and decreased litter weight at 14 days of age,
and if response to selection on this maternally influenced trait could
be accurately predicted.
Data were collected on litter size at birth and weight at birth,
14 days, and weaning over four selected generations.
Results of the analyses indicated that, at best, genetic improvement
for litter size, weights at birth, 14-days and weaning would
be slow. The heritability estimates from pooled data on selected
lines were 0.11 ± 0. 23, 0.37 ± 0. 27, 0.05 ± 0.05 and 0.43 ± 0. 24
for litter size and weight at birth, 14 days and weaning, respectively.
Heritability estimates in the control lines for litter size and weight
at birth, 14 days and weaning were 0.1 2 ± 0.17, 0. 24 ± 0. 34,
0. 29 ± 0.12 and 0.06 ± 0.02 respectively. The data indicate that selection for 14-day weight will have
little effect on changes in litter size and litter birth weight but a
slight response in weaning weight and gain from 14-days to weaning
could be expected. There was a genetic correlation of 0.59 ± 0.35
between 14-day weight and weaning weight.
The major portion of the variability in 14-day and weaning
weights (62% and 63%, respectively) was due to maternal effects.
Cross fostered progeny reared by high, control and low line dams
from generation 4 averaged 6.95, 6.45 and 5.34 grams, respectively.
There were no differences between high, low and control line
progeny when they were reared by either a high, control or low line
dam. It was concluded that selection had increased milk yield in
dams from lines selected for increased 14-day weight and decreased
milk yield in dams from lines selected for reduced 14-day weight.
Comparison of observed with predicted 14-day weight and
weaning weight were in excellent agreement in the control line as
shown by a deviation of less than 1%, between observed and predicted.
Lines selected for increased 14-day weight (pooled data) showed that
the observed 14-day weight was approximately 8% below the predicted
14-day weight; however, observed weaning weight was within IN of
the expected weaning weight. Data from low lines (pooled data)
revealed that the observed 14-day weight was nearly 17% below the expected 14-day weight. Also, the observed weaning weight was
17% below the expected weaning weight for progeny from dams
selected for reduced 14-day weight. Comparison of observed and
predicted 14 -day weights and weaning weights revealed that selection
tended to be less effective than expected in lines selected for
increased 14-day weight but more effective than expected in lines
selected for decreased 14-day weight.