Effect of Divergent Selection for Plasma very Low Denstity Lipoprotein Concentration on Reproductive Performance in Broiler Chickens

The reproductive performance and abdominal fat of the high VLDL (H-VLDL) and low VLDL (L-VLDL) lines were studied after divergent selection for plasma very low density lipoprotein (VLDL) concentration in broiler chickens at 8 weeks of age. It was shown that the main reproductive traits were higher in L-VLDL line than H-VLDL line. The beneficial correlated responses of the reproductive traits were produced by the selection for plasma VLDL. 1) Plasma VLDL concentration was significantly correlated with abdominal fat (r=0.50, P<0.01), ahich was higher than that with plasma triglyceride concentration. There was a significant difference in abdominal fat between both lines but age increase or food restriction may decrease this difference. The H-VLDL line had about twice as much abdominal fat as had L-VLDL at 8 weeks of age, while its mean body weight was similar to that of the L-VLDL line from birtl to the end of laying. 2) Mortality from apparently stress-related causes by food restriction for H-VLDL line females began to increase from 15 weeks of age and was 21% (38/180) higher compared with 13% (23/180) for L-VLDL line females. 3) Age of 5% Lying for L-VLDL line was 3 days less than that of H-VLDL line, age of 50% Lying was 37 days less for L-VLDL line than H-VLDL line, and the age of laying peak was similiar in both lines. Rate of lay at peak in L-VLDL and H-VLDL lines were 70.3%, 66.4%, respectively. 4) Fertility rate in L-VLDL line was significantly higher than that of H-VLDL line at 27 weeks of age (P=0.01) and there was a little difference in fertility rates between H-VLDL and L-VLDL line during late laying period. There were no significant differences between H-VLDL and L-VLDL lines in of day-old healthy the numbers chicks and hatchabilities of fertile and total eggs wheres mean numbers of healthy day-old chicks per hen were more is L-VLDL line than in H-VLDL line. 5) Under food restriction, egg production was higher in L-VLDL line than in H-VLDL line. It should be emphasized that the rate and amount of egg production in L-VLDL line were both significant higher than in H-VLDL line during early laying period (from 23 to 43 weeks of age, P<0.01). The mean egg production of LF line hens was ll eggs more than that of HF line ones throughtout the laying period (from 23 to 62 weeks of age). 6) Eggs in L-VLDL line were slightly heavier than those in H-VLDL line. Feed conversion (FC) ratio for L-VLDL line was lower than that in H-VLDL line betwen 23 and 62 weeks of age (5.01 and 5.46, respectively), especially FC ratio of L-VLDL line was significantly lower than that of HF line during 23 and 43 weeks of age (P<0.01). Also FC efficiency of breeding hens was higher in L-VLDL line than in H-VLDL line.

Selective footprints and genes relevant to cold adaptation and other phenotypic traits are unscrambled in the genomes of divergently selected chicken breeds

Background The genomes of worldwide poultry breeds divergently selected for performance and other phenotypic traits may also be affected by,and formed due to,past and current admixture events.Adaptation to diverse environments,including acclimation to harsh climatic conditions,has also left selection footprints in breed genomes.Results Using the Chicken 50K_CobbCons SNP chip,we genotyped four divergently selected breeds:two aboriginal,cold tolerant Ushanka and Orloff Mille Fleur,one egg-type Russian White subjected to artificial selection for cold tolerance,and one meat-type White Cornish.Signals of selective sweeps were determined in the studied breeds using three methods:(1)assessment of runs of homozygosity islands,(2)F_(ST) based population differential analysis,and(3)haplotype differentiation analysis.Genomic regions of true selection signatures were identified by two or more methods or in two or more breeds.In these regions,we detected 540 prioritized candidate genes supplemented them with those that occurred in one breed using one statistic and were suggested in other studies.Amongst them,SOX5,ME3,ZNF536,WWP1,RIPK2,OSGIN2,DECR1,TPO,PPARGC1A,BDNF,MSTN,and beta-keratin genes can be especially mentioned as candidates for cold adaptation.Epigenetic factors may be involved in regulating some of these important genes(e.g.,TPO and BDNF).Conclusion Based on a genome-wide scan,our findings can help dissect the genetic architecture underlying various phenotypic traits in chicken breeds.These include genes representing the sine qua non for adaptation to harsh environments.Cold tolerance in acclimated chicken breeds may be developed following one of few specific gene expression mechanisms or more than one overlapping response known in cold-exposed individuals,and this warrants further investigation.