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Abstract
Summary:-Heat stress induced disturbances of antioxidant defense system in chicken, so the aim of the present study was performed with objectives to determine the antioxidant status of chickens subjected to heat stress in addition to gene expression changes in the liver and evaluate the effects of NAC, vitamin C and vitamin E supplementation in achieving heat tolerance at an early date.
This study was carried out in summary season (August) on one hundred, apparently healthy, one day-old, unsexed Hubbard chicks were used. They were provided by Omat El-Saudia Poultry Company at Sharkia Province. After through cleaning and disinfection, the chicks were housed in a constant environmental under hygienic measures in the experimental poultry unit in Faculty of Veterinary Medicine, Zagazig University, Egypt and fed on a well balanced ration throughout the experimental period (43 days).
The chicks were divided into 2 main classes:
The first class (untreated): This class is subdivided randomly into three main groups as follow:
The first group served as a control for other groups (untreated group & NHST) and reared under ambient temperature (30 ± 2 ºC) daily allover the experimental.
The second group: served as one day heat stress group at 40 ± 2ºC for 2, 3 and 4 hr at 20, 30 and 40 days consecquency.
The third group: served as two days heat stress group at 40 ± 2ºC for 2, 3 and 4 consecutive hours at 20, 30 and 40 days sequence and for 2, 3 and 4 consecutive hours at 21, 31 and 41 days sequence.
The second class (treated): This class is subdivided randomly into three main groups as follow
The fourth group: represented NHST, reared under similar condition of temperature as group I and received a mixture of NAC, Vit. C and Vit.E daily allover the experimental .
The fiveth group: this group exposed to the same conditions of group II and received a mixture of NAC, Vit. C and Vit.E daily allover the experimental .
The sixth group: this group exposed to the same conditions of group III and received a mixture of NAC, Vit. C and Vit.E daily allover the experimental.
Blood samples were drained from wing veins of birds from each group at 21, 31, 41 and 43 days of the experimental period. The samples were collected on heparinized clean, dry vials with a rubber stopper to and separate plasma were centrifuged at 3000 r.p.m. for 15 minutes and the obtained plasma were kept frozen at – 20 ْC until determination of SOD, CAT, GPx, GR, GSH, and MDA, while portion of liver of control and tested animals were wrapped in aluminium foil and put immediately in liquid nitrogen container to make snap-freezing of tissues and minimize action of endogenous RNase to be used for follow up catalase and Mn-SOD gene expression and other portion were homogenated to determine biochemical activity of SOD, CAT, GPx, GR, GSH, Vit.C, Vit.E and MDA.
The obtained results showed that:-
The status of enzymatic and non-enzymatic antioxidants in erythrocytes of broilers are depicted in Table (3a and 4.a). Untreated birds belonging to group II (one day HST) and group III (two days HST) exhibited significantly low activity of blood erythrocyte SOD at 21 and 41 days, CAT at 31 days and GSH levels at 21, 31, 41 and 43 days, while MDA levels at 41 days showed a significant increase when compared with NHST-untreated controls (Group I).
NAC, Vit. C and vit. E combination treated birds of NHST and HST groups (group IV, V and VI) exhibited significantly increased activities of erythrocyte CAT, GPX and GSH levels, while MDA level showed significant decrease when compared with HST-untreated birds (group II and III).
Plasma activities of SOD at 31 & 43 days and CAT at 31 days were significantly decreased, while MDA level at 21 & 31 days showed a significant increase in HST groups (II & III) when compared with group I (Table 5.a and 6.a). It was also observed that NAC, Vit. C and Vit.E. combination treated birds of group IV, V and VI showed significantly higher activities levels of plasma CAT, SOD and GPX levels, while MDA levels showed significant decrease when compared with HST-untreated birds (group II and III).
HST-untreated birds of group II and group III showed significant decrease in the activities of liver SOD, CAT and GR in addition to GSH, vit. C and vit. E concentrations while GPX activity and MDA level showed a significant increase when compared with group I (Table 7).
Similarly, the activities of liver SOD, CAT, GPX and GR, in addition to GSH, vit. C and vit. E levels showed significant increase, while MDA level showed significant decrease which be noticed in NAC, vit. C and vit. E combination treated birds of group IV, V and VI when compared with group II and III.
There were significantly down regulation in pattern of expression of Mn-superoxide dismutase and catalase in both one day heat stress and two days heat stress groups. Meanwhile, the levels of gene expression of Mn- superoxide dismutase and catalase were increased till reaching near to the control value after treatment in other groups.
It can be concluded from the present study that supplementation of antioxidants (NAC, vit. C, and vit. E) in broiler feed exerts a heat stress ameliorating effect through alteration in both enzymatic and non-enzymatic antioxidative systems of erythrocytes, plasma and liver tissue. The enzymatic profile of these tissues suggested that the NAC, vit. C, and vit. E and had highest potential to ameliorate oxidative stress in broilers under heat stress.