Restriction fragment length and single strand conformational polymorphisms in chicken mitochondrial phosphoenol-pyruate carboxykinase gene and its association with egg production.

This study analysed mitochondrial phosphoenol-pyruate carboxykinase (PEPCK-M) gene as a candidate QTL for egg production traits in chickens. Single Strand Conformational Polymorphism (SSCP) of a 300 bp DNA fragment, from exon 9 of samples from an egg laying North American commercial White Leghorn stock, revealed a total of 6 different single strand conformers, indicative of 3 alleles. Subsequent DNA sequencing found a total of 4 base changes in this fragment between these alleles (called A1, A2 and A3) when compared to the reference sequence published online. The A1 allele had one transition mutation of T to C at position 1700. The A2 allele had accumulated three transition mutations: T to C at position 1578, A to G at position 1647 and T to C at position 1650. Transition mutation of T to C at position 1578 of the A2 allele results in the loss of an AccI site, hence, producing a de novo RFLP. Analysis of 358 female individuals from this strain showed that the population is highly polymorphic at this site. The effect of PEPCK-M genotypes at this site, namely AccI -/-, AccI +/- and AccI +/+, was tested on three traits, age at first egg, egg production rate and egg number. Least square analysis showed that exon 9 RFLP significantly affects age at first egg (p < 0.05). Egg production rate and egg number traits were not affected by different genotypes at this position. The data also indicates an over-dominance effect for the associated trait.

Relationship between Marek's disease and the time course of viral genome proliferation in feather tips.

A total of 114 male chickens from three sire families of a commercial cross of White Leghorn chickens were infected with RB-1B Marek's disease (MD) virus at 21 days of age by exposing them to chickens previously inoculated with MD virus. The presence of virus in feather tips, feather pulp, and MD viral antibodies indicated all chickens became infected. The first virus-positive chickens were observed at 12 days postexposure (dpe). The frequency reached a maximum at 27 dpe and then decreased. At 80 dpe, when the experiment was terminated, no viral DNA was detected in the feather pulp of the surviving chickens (82%). Death from MD was first observed at 38 dpe and reached 18% by the end of the experiment, with spleen lesions being the major MD lesion. The viral genome titers in spleen extracts of chickens with MD lesions was negatively correlated with the time of death, and, similar to feather pulp, none of the surviving chickens was virus positive at the end of the experiment. Quantization of the viral genome titers in feather tip extracts at 27 and 38 dpe revealed a positive correlation with the presence of MD lesions, but only in the declining phase (38 dpe) and not at the peak (27 dpe) of the viral titer. Sire effects were significant, indicating the presence of genetic factors that affect viral proliferation. Again, significance was only observed at 38 dpe and not at 27 dpe. The results indicate that, in this commercial line, 1) all chickens were susceptible to infection via contact exposure, 2) all surviving chickens recovered from the viral infection, and 3) it is not sufficient to measure viral titers at a single time point when using viral titers as an endpoint for MD susceptibility.

Cloning of duck PRL cDNA and genomic DNA.

Complementary DNA (cDNA) and genomic DNA, including flanking regions of the prolactin (PRL) gene of domesticated duck, were cloned and sequenced. Duck PRL was found to have 92.0, 91.7, and 91.4% sequence identity at the cDNA level to PRL of chicken, turkey, and quail, respectively. The predicted amino acid sequence had an overall similarity with a comparable region of chicken (93.4%), turkey (91.3%), and quail (91.3%) PRL. Mature duck PRL contains the consensus sequence for N-linked glycoslylation at position 6 which is not present in either chickens or turkeys. Thus, duck PRL is likely to be post-translationally modified differently from other avian species. Based on the cDNA sequence, the genomic structure of the gene was characterized. The duck PRL gene consists of 5 exons and 4 introns. Moreover, sequence analysis of the proximal region of duck PRL promoter revealed a high degree of similarity to that of chicken and turkey PRL promoter. These results suggest that the mechanisms, which regulate expression of the PRL gene, may be widely conserved in avian species.