The current study was performed to investigate the influence of different stocking density rates on the performance, thermophysiological measurements as well as blood parameters of 0 to 30 d of age female Ross broiler. A total of 96 chicks were randomly distributed in a randomized complete block design among 12 cages. Three stocking density rates were applied; low (28.0 kg/m 2 ), medium (37.0 kg/m 2 ) and high (40.0 kg/m 2 ). Results revealed that cumulative body weight gain (BWG) and feed intake (FI) were influenced (P<0.01) by the rate of stocking density, while no effect (P>0.05) were observed for broilers mortalitycorrected feed conversion ratio (FCR). Higher BWG (P<0.01) and FI (P<0.05) were reported for low and medium density rates broilers in comparison to the high density rate broilers. Overall means of body temperature as well as head, neck, wing, body and shank surface temperatures have displayed (P<0.05) higher values in medium and high density rates broilers compared to the low density rate broilers. Furthermore, increasing the stocking density from 28 to 40 kg/m 2 induced a state of hemodilution in higher density rate broilers, which might explain the noticeable decrease in packed cell volume (PCV). Meanwhile, an increase in serum aspartate aminotransferase (AST) was observed in the higher density group, which might indicate hepatocellular injures. It can be concluded that increasing the stocking density rate from 28 to 40 kg of BW/m 2 had evident impingement effects on the performance of broiler chicken and could jeopardize their welfare.
Background Hybridisation and introgression play key roles in the evolutionary history of animal species. They are commonly observed within several orders in wild birds. The domestic chicken Gallus gallus domesticus is the most common livestock species. More than 65 billion chickens are raised annually to produce meat and 80 million metric tons of egg for global human consumption by the commercial sector. Unravelling the origin of its genetic diversity has major application for sustainable breeding improvement programmes. Results In this study, we report genome-wide analyses for signatures of introgression between indigenous domestic village chicken and the four wild Gallus species. We first assess the genome-wide phylogeny and divergence time across the genus Gallus. Genome-wide sequence divergence analysis supports a sister relationship between the Grey junglefowl G. sonneratii and Ceylon junglefowl G. lafayettii. Both species form a clade that is sister to the Red junglefowl G. gallus, with the Green junglefowl G. varius the most ancient lineage within the genus. We reveal extensive bidirectional introgression between the Grey junglefowl and the domestic chicken and to a much lesser extent with the Ceylon junglefowl. We identify a single case of Green junglefowl introgression. These introgressed regions include genes with biological functions related to development and immune system. Conclusions Our study shows that while the Red junglefowl is the main ancestral species, introgressive hybridisation episodes have impacted the genome and contributed to the diversity of the domestic chicken, although likely at different levels across its geographic range.
The red junglefowl Gallus gallus is the main progenitor of domestic chicken, the commonest livestock species, outnumbering humans by an approximate ratio of six to one. The genetic control for production traits have been well studied in commercial chicken, but the selection pressures underlying unique adaptation and production to local environments remain largely unknown in indigenous village chicken. Likewise, the genome regions under positive selection in the wild red junglefowl remain untapped. Here, using the pool heterozygosity approach, we analyzed indigenous village chicken populations from Ethiopia, Saudi Arabia, and Sri Lanka, alongside six red junglefowl, for signatures of positive selection across the autosomes. Two red junglefowl candidate selected regions were shared with all domestic chicken populations. Four candidates sweep regions, unique to and shared among all indigenous domestic chicken, were detected. Only one region includes annotated genes (TSHR and GTF2A1). Candidate regions that were unique to each domestic chicken population with functions relating to adaptation to temperature gradient, production, reproduction and immunity were identified. Our results provide new insights on the consequence of the selection pressures that followed domestication on the genome landscape of the domestic village chicken.
42Hybridization and/or introgression play a key role in the evolutionary history of animal species. 43 It is commonly observed in several orders in wild birds. The domestic chicken Gallus gallus 44domesticus is the commonest livestock species exploited for the benefit of mankind. The origin 45 of its diversity remains unsettled. Here, we report a genome-wide analyses for signatures of 46 introgression within domestic village chicken. We first established the genome-wide 47 phylogeny and divergence time across the genus Gallus, showing the sister relationships 48between Grey junglefowl G. sonneratii and Ceylon junglefowl G. lafayettii and that the Green 49 junglefowl is the first diverging lineage within the genus Gallus. Then, by analysing the whole-50 genome sequences of geographically diverse chicken populations, we reveal extensive 51 bidirectional introgression between Grey junglefowl and domestic chicken and to a much less 52 extent with Ceylon junglefowl. A single case of Green junglefowl G. varius introgression was 53 identified. These introgressed regions include biological functions related to the control of gene 54 expression. Our results show that while the Red junglefowl is the main ancestral species, 55introgressive hybridization episodes have impacted the genome and contributed to the diversity 56 of domestic chicken, although likely at different level across its geographic range. 57
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