Effects Of Hatching Weight And Dietary Concentrations Of Methionine On Growth, Immunity, Antioxidant Ability Of Broiler Chickens

The study was conducted to investigate the effects of hatching weight (HW) on the growth, immune function and antioxidant ability of broilers. Besides, diets containing two different concentrations of methionine were formulated to study the nutritional effects of dietary methionine on the growth, immunity and antioxidant ability of broilers that differ in HW. The aim of this study was to supply a laboratory basis for the exploitation of HW on the growth and development of broilers and the application of methionine in poultry. The study includes three trials and the results are presented as follows:The first study was conducted to investigate the effects of HW on the growth, immune function and antioxidant ability of broilers. Day-old male Arbor Acres broilers obtained from the same maternal flock (52wk old) were weighed individually and were separately divided into two groups on the basis of HW (High HW group:51.30±0.21g; Low HW group:42.97±0.11g) and each of which had8pens of10chicks per pen. The experiment lasted for21d. Body weight (BW) of broilers with high HW were higher than those birds with low HW throughout the experiment with broilers with high HW had a significantly higher BW at7and14d of the experiment (P<0.05), rescepectively, but average daily gain (ADG), average daily feed intake (ADFI) and feed/gain ratio (F/G) of broilers were unaffected by HW in either period of the experiment and throughout the experiment. Broilers in high HW group had a higher concentration of total protein (TP) at14d (P=0.019), globulin (GLB) at14d (P=0.025) and albumin (ALB) at7d (P=0.033), respectively. However, Blood urea nitrogen (BUN) of broilers was unaffected by HW (P>0.05). Relative weights of immune organs, serum lysozyme (LZM) content, anti-New castle disease virus titers (Anti-NDV titers) and immunoglobulin G (IgG) concentration were all unaffected by HW (P>0.05), besides, serum cortisol and thyroid hormones concentration were also unaffected by HW (P>0.05). Serum superoxide dismutase (SOD) activity, malondialdehyde (MDA) and uric acid (UA) content were all unaffected by HW (P>0.05). Glutathione peroxidase (GPX) activity and reduced glutathione (GSH) content in both serum and liver as well as glutathione disulfide (GSSG) content in liver were unaffected by HW (P>0.05). However, the ratio between reduced glutathione and glutathione disulfide (GSH/GSSG) in the liver of broilers with high HW was significantly higher on the day of7d when compared with those broilers with low HW (P=0.037).The second study was conducted to investigate the influences of dietary concentrations of methionine on the growth performance and immune function of broiler chickens with different HW. Male Arbor Acres chicks obtained from the same flock at47wk of age were weighed individually and were separately divided into two groups on the basis of HW and each HW group included two subgroups with similar HW (High HW group:48.35±0.09and48.25±0.10g; Low HW group41.83±0.05and41.63±0.05g). Each subgroup consisted of6replicates with10birds in per replicate. Birds from each subgroup in the two HW groups were given a diet containing4.9or5.9g/kg methionine for21d, respectively. The results indicated that BW of broilers with high HW were heavier than those broilers with low HW throughout the experiment (P<0.05). ADG and ADFI of broilers from d15to21and d1to21were significantly higher in the high HW group when compared with broilers with low HW (P<0.05), besides, from d8to14, broilers with high HW had a lower F/G than that of broilers with low HW (P=0.048). Diet containing5.9g/kg methionine significantly enhanced BW of broilers with low HW at d21(P<0.05) and ADG from d1to21(P<0.05), and improved feed utilization of birds with low HW from d8to14and d1to21(P<0.05). However, growth performance of broilers with high HW was unaffected by dietary methionine content (P<0.05). BUN content of broilers were unaffected by HW and dietary methionine content (P>0.05). Broilers given diet containing5.9g/kg methionine had a significantly higher concentration of serum ALB content at d21(P=0.038). Besides, Serum TP (P=0.031) and GLB content (P=0.020) of broilers with high HW were also significantly enhanced by diet containing5.9g/kg methionine at7d of the experiment. Relative weights of immune organs, serum Anti-NDV titers and serum anti-sheep red blood cell titers (Anti-SRBC titers) were all unaffected by either dietary methionine content or HW (P>0.05). But serum IgG concentration of broilers was enhanced by diet containing5.9g/kg methionine at7d of age (P=0.021). Compared with broilers with high HW, broilers with low HW had a relative lower serum LZM content (P=0.049), but a higher cutaneous basophilic hypersensitivity response (CBH)(P=0.007) at d21.The third study was conducted to study the effects of dietary concentrations of methionine on the antioxidant capacity of broiler chickens with different HW. The results showed that serum cortisol and thyroid hormones concentration were all unaffected by either dietary methionine concentration or HW (P>0.05). Total antioxidant capacity (T-AOC), SOD activity and MDA content either in liver or serum were all unaffected by HW (P>0.05), UA content was unaffected by HW and dietary methionine content (P>0.05). Diet containing5.9g/kg methionine enhanced serum SOD activity (P=0.002) at d7and decreased liver MDA content at d7(P=0.012) and T-AOC at d21(P=0.035), respectively. Liver GSH and GSSG content as well as glutathione reductase (GR) and GPX activity were all unaffected by HW (P>0.05). Liver GSH content at d7(P=0.034) and GPX activity at d21of broilers with high HW (P=0.033) were decreased by diet containing5.9g/kg methionine. However, the GSH/GSSG in the liver of broilers (P=0.049) at d21and liver GSH content of broilers with low HW (P=0.034) were increased by diet containing5.9g/kg methionine.In conclusion, these results indicated that there existed considerable variations among broilers with different HW regarding performance, immunity and antioxidant capacity and high dietary content of methionine can exert a beneficial influence on the growth and immunity as well as antioxidant status of broiler chickens.