Résumé:
The present study is realized to assess the effects of precocious and chronic
expositions of broilers chicken at a high temperature on the growth performances, the
carcass parameters, the deposit and the fatty acids composition of lipids subcutaneous (LSC),
the plasma parameters and the hormone levels. Three hundred male chicks (Hubbard) were
raised during fifty days. They were devised into three groups (each group contained one
hundred chicks). The chronic thermal ambient were applied starting from the 8th day of
rearing to know a thermo-neutrality (TN: 25±2°C) for the first group, a summer moderate
temperature at about (TM: 32±2°C) for the second and a higher summer temperature (TH:
37±2°C) for the third. The mortality after 7 hours of heat shock (40±1°C) was determined on
the 51th day according two adaptation approches (First approch: early and chronic exposure
chickens to heat. The second approch: early exposure chicks 3 or 5 days of age to heat,
39°C/24 hours).
The results obtained were summarized as follows: 1- After 40 days, a decline of feed
intake (37g/day) due to TH is observed. 2- The superiority of body weight in broilers TN is
recorded as from the 40th day. 3- Compared to the early rearing, a daily improved weight
gain is observed in broilers TH at the end. 4- In comparison with other temperatures, the
feed conversion ratio of broilers TH was significantly better from 40 days. 5- At the end of
rearing, the comparables carcass yields (EC/BW) were recorded in broilers TN and TH. 6- At
the end of rearing, a decrease of the PM weight linked to the TH is observed (-17 and -20%
compared to TM and TN respectively). 7- A higher subcutaneous lipids (SCL) deposit occurs
in broilers TH especially in the end of rearing reaching 105g/Animal; this is translated by a higher SCL/EC report in broilers TH (+7.3% compared with TN). 8- Inversely after 32 days of
age, the weight of abdominal fat was higher in broilers TN. 9- Compared to broilers TN, an
increase proportion of saturated fatty acids (SFA) and poly unsaturated fatty acids (PUFA) of
SCL is obtained in broilers TH of 50 days. No temperature effect on the proportion of mono
unsaturated fatty acids (MUFA) of SCL has been observed. Finally, the TH caused a significant
of UFA/SFA reflecting a higher saturation degree of SCL in carcass broilers TH. 10- Increase in
the concentration of aldosterone and ACTH and decreased concentration of thyroid
hormones and insulin in broilers TC are observed especially during growth. 11- These results
have shown that broilers can tolerate chronic high temperature (37°C). Indeed, a better rate
of mortality was recorded after heat shock with first approch to adaptation.
