Results
Live Body Weight and Muscling
Additive Genetic Effects. The 17-week body weight of the A line did not differ significantly from that of the B line for males (Table 1) or females (Table 2) when the sexes were analyzed separately. However, in the combined analysis, Line A was larger than Line B (Table 3). The F line was smaller than the A line in all three analyses. The F line did not differ significantly from the B line when the sexes were analyzed separately but the B line was significantly larger than the F line when the sexes were combined.
Carcass breast width and the weight of the breast muscles (P. major and P. minor) were larger and breast rating was smaller for the commercial sire lines than for the F line for males, females, and sexes combined (Tables 1 to 3). The commercial sire lines did not differ for carcass breast width, weight of the P. major muscle, or breast rating for males, females, or sexes combined. The weight of the P. minor muscle did not differ between commercial sire lines for males but was significantly larger in Line A than Line B for females and sexes combined.
The weight of the thigh muscles was larger in the commercial sire lines than in the F line for males (Table 1) and sexes combined (Table 3) but not for females (Table 2). The weight of the drumstick muscles did not differ significantly between the commercial sire lines and the F line in males, female, and sexes combined even though the average weights were consistently larger for the commercial sire lines than the F line.
Reciprocal Effects. Reciprocal effects were not significant for body weight, muscle weights, carcass breast width, and breast rating in males (Table 1) and sexes combined (Table 3). Reciprocal effects were significant for the weight of the drumstick muscles for females in both crosses and thigh muscles for females from the crosses of the B and F lines (Table 2). In all cases when reciprocal effects were significant, values were greater when the commercial sire line was the female parent.
Heterotic Effects. The percentage heterosis for 17-week body weight was significant for males (average = 7.2, Table 1) and sexes combined (average = 3.6, Table 3) but not for females (Table 2). Carcass breast width, breast rating, and weight of the P. major muscle exhibited significant heterosis for males of the crosses of the A and F lines but not the B and F lines. No significant heterosis was noted for breast width, breast rating, or weight of the P. major muscle for females in either cross. When the data were analyzed for the sexes combined, the breast ratings and the weight of the P. major muscle, but not carcass breast width, exhibited significant heterosis in the crosses of the A and F lines and significant heterosis was observed for the weight of the P. minor muscle in the crosses of the B and F lines. In general, the weights of the leg muscles (drumstick and thigh) exhibited significant heterosis for males and females separately and for sexes combined. The percentage heterosis was positive (6.5), but not significant, for the drumstick muscles of females from the crosses of the B and F lines.
Leg Measurements
Additive Genetic Effects. All leg bones were consistently heavier in the A line than in the B line but the differences were not significant for males (Table 4). For females, the tibiotarsus and femur weights were significantly larger in the A line than in the B line (Table 5). When the data from both sexes were combined (Table 6), the weights of all leg bones were heavier in Line A than in Line B. The width of the tarsometarsal bone did not differ between the A and B lines in males, females, or sexes combined. The tarsometarsal and femur bones were longer in the A line than in the B line in the analysis in which sexes were combined. In males, only the length of the femur differed significantly between Lines A and B and there was no significant line difference in length of the femur and tarsometarsal bone in females. No significant difference between the A and B lines was noted for length of the tibiotarsal bone.
The femur weight and tibiotarsal bone weight and length were greater in the F line than in the A line for males (Table 4) and sexes combined (Table 6) but there was no line difference for females (Table 5). There was no significant difference between the F and A lines for tarsometarsal width.
All of the leg bones were heavier in the F line than in the B line for males (Table 4), females (Table 5), and sexes combined (Table 6). The tarsometarsal and femur bones were longer in the F line than in the B line for males, females, and sexes combined. The tibiotarsal bone was, in general, longer in the F line than in the B line with the difference being significant for females separately and when the sexes were combined. There was no difference between the F and B lines for tarsometatarsal width.
Reciprocal Effects. No significant reciprocal effects were observed for leg bone weights and lengths when the data for males were analyzed separately (Table 4). For females (Table 5), the reciprocal crosses of the A and F lines differed in sistently larger for Line A than for Line B but was significant only for females and the sexes combined.
The F line did not differ from the commercial sire lines in keel length (Tables 7, 8, and 9). Body Depth 1 was consistently larger in the F line than the commercial sire lines. Only for females of the crosses of the A and F lines was the difference not significant. Body Depth 2 of the commercial sire lines and the F line did not differ resulting in a significant differences between the commercial sire lines and the F line in body depth ratio in all comparisons. The body cavity was longer in Line F than in Line B but there was no line difference between Lines A and F. Body cavity width did not consistently differ between the commercial sire lines and the F line with a line difference being significant only for females from the crosses of the B and F lines. The body cavity was consistently higher in the F line than in the commercial sire lines. Although not always statistically significant, the F line had a greater body cavity volume than the commercial sire lines with the difference being larger in the comparisons of the B and F lines.
Reciprocal Effects. Reciprocal effects were not an important source of variation in measurements of body shape (Tables 7, 8, and 9). For males, the only significant differences between reciprocal crosses was observed were for body cavity width in the crosses of the A and F lines and for Body Depth 1 in the crosses of the B and F lines. No significant reciprocal effects were noted for females in either cross. In the combined analysis of both sexes, significant reciprocal effects were noted for keel length in the crosses of the B and F lines.
Heterotic Effects. Heterosis in keel length was positive in all comparisons (Tables 7, 8, and 9) but was significant only for the analysis of the sexes combined in the crosses of the B and F lines. Body Depth 1 did not exhibit significant heterosis but heterosis for Body Depth 2 was consistently positive (range = 2.1 to 3.5%) in all comparisons and significant for the sexes combined in the crosses of the A and F lines. Heterosis for body depth ratio was consistently negative (range = -1.5 to - 4.3%) and was significant for males and sexes combined in the crosses of the A and F lines. No significant heterosis was observed for body cavity length, body cavity width, body cavity height, or body cavity volume.