Factors influencing early poult flip-overs in experimental populations of turkeys.

A large number of poults from a line (E) selected long-term for increased egg production were observed, in recent generations, to flip over during the week immediately after hatching. This condition, termed early poult flip-overs (EPF), is characterized by the poults falling on their back and being unable to right themselves without assistance. Poults that flip over more than once appear to lack neurological control, lying on their backs with their legs paddling. If handled, the affected poult moves its head laterally and after several seconds appears to go to sleep. When placed on litter, the poult has no sense of balance and falls to one side or the other and starts paddling its feet. Poults that flip over may also chirp loudly. Observations from previous years indicate that no bacterial infectious agent was associated with the EPF condition. Affected poults have increased mortality relative to normal poults that do not flip over. The objective of the present study was to evaluate the effects of inheritance, beak trimming, hatching time, genetic growth potential, and poult hydration on the incidence of EPF. The E line had a greater incidence of EPF than its randombred control line, indicating the possibility of a genetic basis for the condition. However, within the E line, the heritability, based on variation among full-sib families, of the occurrence of EPF (assuming that EPF is an all-or-none trait) was low, being 0.044 and 0.052 in 2 consecutive yr. The heritability of the number of days (out of five) a poult continued to flip over was somewhat higher [0.26+/-0.002 (SE)]. Genetic growth potential may influence incidence of EPF for, when the E line was crossed with a large-bodied experimental line selected for increased 16-wk BW, the frequency of EPF was reduced and BW at 13 d of age was increased in the cross relative to the pure E line even though poult weight was similar at hatching in the two genetic groups. In the E line, later hatching poults within a hatch had a greater incidence of EPF than those hatching earlier. Neither beak trimming with an electronic beak trimmer nor poult hydration influenced EPF.

Range and confinement rearing of four genetic lines of turkeys. 1. Effects on growth, mortality, and walking ability.

Line by environment interactions complicate interpretation of results from long-term selection experiments. To investigate the potential effects of such interactions, a study was conducted in which birds from four genetic lines were reared in two environments. Birds from four turkey lines were brooded in confinement housing. At 8 wk of age, half of the birds from each full-sib family were moved to a large range pen and the remainder were placed in a large confinement pen. Significant line by environment interactions were present only for walking ability scores of males. A general lack of significant line by environment interactions indicates that rearing environment of these lines may be altered without affecting interpretation of results from a selection experiment. In addition, the current randombred control lines continue to adequately serve as control populations for a long-term selection experiment.

Spontaneous autoimmune thyroiditis in chickens. I. Effects of bursal reconstitution.

Chicks from strains genetically susceptible or resistant to spontaneous autoimmune thyroiditis were neonatally treated with cyclophosphamide to induce lymphocytic depletion of the bursa of Fabricius. The subsequent bursal repopulation with B cells from donors matched at the major histocompatibility locus showed B cells to be intricately associated with the pathogenesis of spontaneous autoimmune thyroiditis, although they themselves did not carry the potential for initiation of the disease.

Genetic influences on spontaneous autoimmune thyroiditis in (CS X OS)F2 chickens.

Genetic effects on spontaneous autoimmune thyroiditis in chickens were assessed by measuring phenotypic symptoms, the titer of circulating antibody to thyroglobulin, and the pathological change in the thyroids of young chicks. One or more loci within the B complex (the major histocompatibility complex of the chicken) are responsible for the expression of autoimmunity, and evidence is provided for an interaction of the B haplotype with genes at other loci. The influence of the B complex component on genetic susceptibility is more visible in animals with limited susceptibility at other loci and becomes indistinguishable as the frequency of other genes determining thyroid autoimmunity increases.

Changes in relative aggressiveness and social dominance associated with selection for early egg production in chickens.

We tested the hypothesis that artificial selection for early reproductive performance of chickens kept under competitive conditions increases aggressiveness and social dominance. Two populations subjected to long-term selection for number of eggs laid before 40 weeks of age and the unselected control population from which they derived were used. Results generally supported the hypothesis but indicated that increased aggressiveness associated with such selection may characterize the adolescent period only. For one of the selected strains, rank for aggressiveness and social dominance between adolescence and full maturity was reversed, relative to the control population. Associations between increased aggressiveness (and social dominance) and decreased age at sexual maturity are discussed, along with implications as to the role of social status and reproductive performance when different genetic strains compete within flocks.