|Abstract or Summary
- Five lines of turkeys with wide variation in body size, reciprocal
crosses between large and small lines, and backcrosses to the
large parent line were studied to determine the effect of body size
and crossbreeding on growth rate, conformation, feed consumption,
organ size, and other physiological traits.
Selection was made on the basis of body size only. The largest
turkeys were selected in the large lines and the smallest turkeys were
selected in the small lines. Decreases in fertility were observed in
the large lines but not in the small lines of turkeys during the three
year study. Hatchability decreased in all lines. Crossing produced
no heteros is in fertility or hatchability.
Inheritance of 20 week shank length was quantitative. Wide
variations were found in 20 week body weights. Differences in the
slope of the regression line is a measurement of the rate of gain in
body weight compared to the rate of gain in shank length. The larger
lines had steeper slopes from four to eight weeks of age. Weight
gain in proportion to shank length growth was greater in the large line
than in the small line from four to eight weeks of age. The smaller
lines had steeper slopes after 12 weeks of age. Body weight gain in
proportion to shank length growth during this period in the small lines
was higher because of the greatly reduced rate of growth in shank
Adrenal, gonad, heart, pituitary, and liver weights were significantly
affected by age, sex, and line of the turkeys. However, no
differences were found between slopes of the regression lines of log
organ weight on log body weight. Thyroid weight was significantly
affected by age but not by sex or line. The slope of the regression of
log thyroid weight on log body weight was significantly steeper in the
next to smallest than it was in the females in the next to largest line.
With one exception, a negative correlation was found between
hematocrit value and body weight. Hematocrit values of young males
and females in the largest line were significantly lower than the
hematocrit values of the other lines. The hematocrit values of adult
females in the smallest line were lower than normal for the size of
the turkeys. It is possible that this line has a lower than normal
metabolic rate. However, no significant differences were found in
rectal temperature between lines. Feed consumption of adult females was in proportion to body
size and egg production. Feed conversion of young turkeys in the
smallest line was significantly higher than the other lines. The feed in
efficiency of these turkeys was not transmitted to the backcross line.
Differences in muscle cell size were found between the largest
and the smallest lines of turkeys. However, differences in muscle
cell size did not account for all the differences in body weight between
or within lines.
In proportion to other long bones in the skeleton, the tarsometatarsus
of the hen in the smallest line was short. This may be
related to a lethal mutation which was found in high frequency in that
line. The mutant has a parrot beak and short, thick appendages. The
data indicate that it is caused by a single autosomal recessive gene.
Because of the phenotypic similarity between this mutant and micromelia
mutants in chickens and quail mi, the mutant gene was similarly
designated mi for micromelia.