Results
Hatch effects were significant for body weight at 8, 16, and 20 weeks of age, breast width, and walking ability scores of males (data not shown). For females, hatches differed significantly for 8-week body weight, shank measurements (length, depth, and width), and breast width (data not shown).
Additive Genetic Effects
Comparison of Lines A and B. For males, Line B was larger at 8, 16, and 20 weeks of age, had wider breasts, and poorer walking ability (higher walking ability score) than Line A (Tables 1 and 3). There was no difference between lines for any shank measurements of males. For females, Line B had wider breasts and wider shanks than Line A but there was no significant line differences in body weight at any age, shank length and depth, and walking ability scores (Tables 2 and 4).
Comparison of Lines A and F. The F line was heavier than the A line at 8 weeks of age with the difference being significant (P < 0.01) only for males (Tables 1 and 2). By 16 weeks of age, both males and females of the A line were heavier than those of the F line and the line difference continued to increase at 20 weeks of age. For males, the F line had longer shanks, narrower breasts, and higher walking scores than the A line (Table 1). There was no line difference in shank width and shank depth of males. Females of the F line had longer narrower shanks than females of the A line, but walking ability score did not differ between lines (Table 2). The breasts of females were narrower in the F line than in the A line.
Comparison of Lines B and F. The B and F lines were similar in body weight at 8 weeks of age but the B line was larger than the F line at older ages (Tables 3 and 4). At 16 weeks of age, the B line had wider breasts in both sexes. The shank was longer for both sexes in the F line than in the B line. There was no significant line difference in walking ability scores in either sex. Shank width of the B line was greater than in the F line only for females.
Reciprocal Effects
No difference between reciprocal crosses was noted in the crosses of the A and F line for any trait, except for breast width of males (Tables 1 and 2). For the crosses of the B and F lines, reciprocal effects were significant for shank width and depth of males (Table 3) and for 8-week body weight and shank depth of females (Table 4).
Heterotic Effects
Heterosis was an important source of variation in body weight of males from the crosses of the A and F (Table 1) and of the B and F lines (Table 3). The percentage heterosis at the various ages ranged from 6.2 to 7.5 for the A X F crosses and 3.1 to 5.8 for the B X F crosses. Overdominance (i.e., the weight of the crosses was greater than either parental line) occurred at all ages in the A X F crosses and at 8 weeks of age in the B X F crosses. For females of the A X F crosses, heterosis in body weight was significant with overdominance only for 8-week body weight (4.4 %, Table 2), while in the B X F crosses heterosis in body weight was significant at 8 (4.9 %) and 16 (2.6 %) weeks of age (Table 4).
In the crosses of the A and F lines, heterosis was not significant for walking ability scores, shank length, and breast width of both sexes (Tables 1 and 2). Heterosis for shank width and shank depth was significant for males but not females in the A and F crosses. Negative heterosis for walking ability score was observed in males from the B X F crosses (Table 3), but no significant heterosis was observed in females of this cross (Table 4). Heterosis was significant for all shank measurements in males from the B X F crosses (Table 3), but only for shank length of females (Table 4). No significant heterosis was observed for breast width in either sex of the B X F crosses (Tables 3 and 4).