Effect of crossbreeding on fertility, hatchability and embryonic mortality of Nigerian local chickens

Transcriptional profiling of the M. complexus in naked neck chickens suggest a direct pleiotropic effect of GDF7 on feathering and reduced hatchability

BACKGROUND

The locus for naked neck (Na) in chickens reduces feather coverage and leads to increased heat dissipation from the body surface resulting in better adaptability to hot conditions. However, the Na gene is linked to significantly lower hatchability due to an increased late embryonic mortality. It has been argued that the causative gene GDF7 may have a direct pleiotropic effect on hatchability via its effect on muscle development. Thus, the study presented here analyses the transcriptome of the hatching muscle (M. complexus) and shows how GDF7 impacts development leading to reduced hatching rates in Na chickens.

RESULTS

Using 12 chicken embryos (6 x wildtype (Wt) and 6 x Na) RNA was extracted from the M. complexus of each embryo and sequenced. The resulting differential expression analyses led to the discovery of 461 differentially expressed (DE) genes in the M. complexus of the experimental group. Among those, 77 genes were of uncertain function (LOC symbols), with 31 were classified as uncharacterised. The regulation of a number of pathways involved in normal embryonic development, were found to be negatively influenced by the Na genotype. Further pathways involved in cell-cell adhesion, cell signalling pathways, and amino acid (AA) metabolism/transport were also observed. GDF7 (alias BMP12), whose localised overexpression in the neck skin causes the Na/Na phenotype, was significantly overexpressed in the M. complexus of Na/Na embryos, and shows a significant increase in the number of binding sites for the transcription factor PITX2 was also observed.

CONCLUSION

In Na chickens, GDF7 is under the control of a mutated cis-regulatory element, whose actions are known to suppress the development and distribution of feathers through the sensitizing action of retinoic acid. In this study, a number of DE genes with over 10 retinoic acid response elements (RAREs) in close proximity were observed, indicating changes to the retinol metabolism. With the understanding that the Na/Na mutation leads to increased retinoic acid activity, this indicates a high likelihood of GDF7 excerpting a direct pleiotropic effect, not just in the observed reduction in feather patterning, but also impacting the development of the M.complexus, and consequently leading to the reduced hatchability observed in birds with the Na/Na genotype. Furthermore, the enrichment of PITX2 binding sites in proximity to DE genes in the M. complexus, also indicates that muscle development is still ongoing in Na embryos. This suggests that the M. complexus is not yet fully developed, further increasing the potential for late embryonic mortality in Na chicks at hatching.

Evaluation of reciprocal F1 crosses of Fayoumi with two exotic chicken breeds 2: additive and non-additive effects on egg quality traits

The current study evaluates additive and non-additive genetic variances for egg quality traits in six genotypes generated through pure mating and reciprocal crossing of Fayoumi (FM) with Koekoek (KK) and White Leghorn (WL). For each genotype, measurements were taken on 30 eggs randomly sampled at 32, 36, and 40 weeks of age to evaluate both external and internal egg quality parameters. The results revealed significant differences (P < 0.001) among the genotypes in all external quality traits and most internal quality traits, including yolk weight (YW), albumen weight (AW), and yolk height (YH). The results also showed that variations due to purebred effect (PE), general combining ability (GCA), maternal effect (ME), and specific combining ability (SCA) were significant in most traits, which reflects that both additive and non-additive variances are important for the inheritances of the parameters investigated. In most of the traits, the ME and PE were higher in KK and WL, while GCA was higher in KK and FM. The FM x WL had higher SCA than FM x KK. The results suggest the likelihood of genetic improvement in these genotypes through selection and crossbreeding strategies and/or a combination of the two.

Hatchability and growth performances of normal feathered local, Sasso-RIR and their F1-cross chickens managed under on-station condition in southern Ethiopia

The Normal feathered local chicken (LL), Sasso-RIR (SRSR) and their F1-cross (LSR) chickens were hatched to evaluate for egg hatchability, body weight, feed efficiency, and survival rate. After 14 days of brooding, 150 chicks of each genotype were randomly selected and further replicated into five pens in a deep litter grower house consisting of 30 chicks each in a completely randomized design, and evaluated for a period of 16 weeks. Hatchability of fertile eggs was highest for LL (80.0%), intermediate for LSR (68.6%), and lowest for SRSR (55.9%) chickens. The body weight (BW) of chicks at 2 weeks of age was 80.0, 76.3, and 61.5 g/bird for SRSR, LSR, and LL, respectively, the latter being the lowest (p < 0.05). The respective BW at 8 weeks of age was 732, 587, and 451 g while at 18 weeks it was 1877, 1379, and 1070 g/bird and different from each other (p < 0.05). During 3- to 8-week and 9- to 18-week growth periods, the LL chickens were inferior (p < 0.05) in feed intake (29.7 and 66.9 g/d/bird) whereas the SRSR chickens were superior (p < 0.05) in body weight gain (15.5 and 16.3 g/d/bird) and feed conversion ratio (2.67 and 5.35 g feed/ g gain), respectively. The mortality rate of chicken was not affected by genotypes. It can be concluded that Sasso-RIR chicken genotype had played a significant role in upgrading the growth rate and market weight of the local normal feathered chicken without adverse effect on hatchability, feed efficiency, and survival rate.