Dwarfism in Diverse Genetic Backgrounds: 2. Behavior and Disease Resistance

Abstract

Investigated were several behavioral and physiological traits associated with the adaptability of dwarf and nondwarf pullets in populations of White Plymouth Rocks that had undergone selection for high (HW) and for low (LW) juvenile body weight. The traits measured were “fear”, head shaking, antibody titers to sheep red blood cells, plasma corticosterone titers, and resistance to E. coli infection. The pullets were reared as floor flocks and then moved into single wire cages (46 × 30 × 46 cm) at 119 days of age in the B4 generation (1975) and 134 days of age in the B5 generation (1976). Significant line-dwarf genotype interactions were found for all traits except fear. There was significantly greater fear noted in the LW than in the HW line and in dwarf than in normal pullets in both generations. Head shaking was significantly greater for normal than for dwarf pullets in both lines in the B4 generation; however, in the B5 generation this difference was significant in the LW line only. Both generations’ antibody titers to sheep red blood cells were greater in dwarf than in normal pullets from the HW line, while no significant differences were noted between genotypes in the LW line. Percentages of mortality plus heart lesions, air sac lesions, and abnormal droppings to an E. coli challenge were greater in the HW line than in the LW line in the B4 generation. In contrast, the response to the E. coli challenge in the B5 generation was greater in the LW than in the HW line pullets. The inconsistency between generations may be explained by differences in the disease histories of the pullets as there was an outbreak of E. necatrix in the B4, but not in the B5 generation.