Effects Of Short-Term Thermal Manipulation During Late Embryogenesis On Hatching Traits And Post Hatched Subsequent Performance Of Mamoura Strain Chicks

The current study was carried out to investigate the effects of short-term thermal manipulation during late embryogenesis on hatchability, chick quality, secondary sex ratio, and some blood biochemical parameters at hatch and after thermal challenge at 60 days of age . A total number of 1200 suitable hatching eggs were taken from Mamoura strain laying hens, Eggs were randomly divided into equal 4 treated groups( 300 eggs each) each treatment were replicated three times (100 eggs each). All eggs were incubated at a constant temperature of 37.5ºC and 55% relative humidity (RH) throughout the incubation period until the end of 15 days, then the second, third and fourth groups were exposed to thermal manipulation (TM) treatment (39ºC and 65% RH) during the 16^th to 18^th days of incubation for 2, 3 and 4 hours per day, respectively, while the first group used as a control (without exposing to heat treatment). After hatching 225 one-day unsexed chicks from each treatment were taken( as same treatments in the hatchery). Chicks of end treatment were  divided into 3 equal  replicates ( 75 chicks each) .and separated reared for 60 days of age. After 60 days of hatch, challenge test (CT) was occurred by raising room temperature into 39 ºC and 65% humidity for 2 hours . Results indicated that thermal manipulation (TM) during late embryogenesis had no significant effect on hatchability traits and embryonic mortality percentages. Male ratio was significantly higher for chickens hatched from the group exposed to TM (39. ºC and 65% RH) for 4 h/d during the 16^th to 18^th days of incubation period. Chick length was significantly(p>0.05) increased for the group exposed to TM for 4 h/d during late embryogenesis, while tibia length was significantly lowered for the same group  compared to all treated and control groups. Body weight and body weight gain were significantly(p>0.05)  higher for chicks hatched from the group exposed to TM for 3 and 4 h/d as compared to2,3h/TM treated groups and  the control group during the period from 30 to 60 days of age. There was no significant differences in body temperature in all TM treated groups and control but chick body temperature at 2 months of age was higher than post hatched chicks. Feed intake was not significantly affected by TM treatment but feed conversion was significantly improved in groups exposed to TM for 3 and 4 h compared to the control and 2h TM treated groups during the period from 30 to 60 days of age . Thermal manipulations during late embryogenesis resulted in significant (p>0.05) decreases in plasma total cholesterol and LDL cholesterol than the control at hatch, while , at 60 days of age , the least plasma cholesterol, and  HDL values were recorded for 4 h TM /d during late embryogenesis. In addit the lowest concentration of plasma LDL was exhibited by birds 2h TM /hr 60 days age. T3 at hatch and 60 days of age ( after CT) and plasma T4 at hatch were significantly decreased due to TM for 4 h/d, While, plasma Triglyceride was significantly decreased due to TM for 4 h/d at 60 days of age after CT. These results suggesting that TM for 4 h/d during the 16^th to 18^th day of incubation period  improve hatching traits, chick quality and subsequent growth performance as well as plasma parameters. It can be concluded that four hours thermal manipulation during 16 to 18 days of incubation period was the best one to initiate improvement of thermo tolerance acquisition, better chick quality low embryonic mortality, and enhanced productivity of chicks at older ages without deleterious effects on blood parameters.