Effects Of Stocking Density And Moderate Temperature On Growth Of Bones And Muscle,Oxidation And Intestinal Morphology In Broiler Chickens

Stocking density and heat stress are two major factors that restricts the intensive development of poultry farming,which have caused widespread concern.The effects of stocking density and moderate temperature on growth of bones and muscle,oxidation and intestinal morphology in broiler chickens were researched in this paper so as to provide theoretical basis for determining scientific and reasonable density and comfortable temperature,which included two tests.The main contents are as follows:1.Effects of stocking density at appropriate temperature on growth of tibia and breast muscle,oxidation and intestinal morphology of broilers in cage.144 22-day-old Arbor Acres?AA?broilers were randomly divided into three groups and transferred to three environment chambers,respectively,with six replicates in each group.The pre-test period lasted for 7 days and broilers were kept at 21°C and 60%relative humidity.When broilers were 29-day-old,the stocking density of low,medium,high groups were 6.25 birds/m²?12.5 birds/m² and 18.75 birds/m²,respectively.The trial period lasted for 14 days with 21°C and 60%relative humidity.The results showed as follows:1)Average daily food intake?ADFI?in high stocking density?HSD?group showed significant lower than that in low stocking density?LSD?group and medium stocking density?MSD?group?P<0.05?,and average daily gain?ADG?in HSD group showed significant lower than that in MSD group?P<0.05?,while there were no significant effects of feed/gain?F/G?in three groups?P>0.05?.2)Compared with LSD and MSD groups,the content of cortisol in serum of broilers in the HSD group was significantly higher?P<0.05?,and the content of alkaline phosphatase?AKP?in serum of broiler chickens in the HSD group was significantly lower?P<0.05?,moreover,the content of3,5,3',5'-tetraiodothyronine?T₄?in serum of broilers in LSD group was distinctly higher than that in the HSD group?P<0.05?,and the level of insulin-like growth factor 1?IGF-1?in serum of broilers in MSD group showed significantly higher than that in the HSD group?P<0.05?.In addition,the expression of parathyroid hormone related peptide?PTHrP?protein in tibial growth plate in the HSD group were significantly lower than in the LSD and MSD groups?P<0.05?,and the HSD group significantly reduced tibial length and weight in broilers?P<0.05?;Compared with LSD and MSD groups,the expression of IGF-1 mRNA and myogenic determining foctor?MyoD?mRNA in the HSD group were significantly lower?P<0.05?,and the expression of myostatin?MSTN?mRNA was significantly higher and the HSD group significantly reduced the proportion of breast muscle in broilers?P<0.05?.3)The activity of glutathione peroxidase?GSH-Px?in serum and liver of broiler chickens in the LSD group was significantly lower than the LSD and MSD groups?P<0.05?,in contrast,the level of malondialdehyde?MDA?in serum and liver of broilers in the HSD group was significantly higher than the LSD and MSD groups?P<0.05?.4)Comparing with LSD and MSD groups,the villus height of jejunum in HSD group was significantly lower and the crypt depth was distinctly higher?P<0.05?.2.Effect of moderate temperatures on on growth of tibia and breast muscle,oxidation and intestinal morphology in broilers.A total of 96 22-year-old AA broilers were randomly divided into two groups and then transferred to two environment chambers,respectively,with six replicates in each group.Each replicate contained eight birds?with four males and four females?.The pretest period lasted for 7 days and broilers were kept at 21°C and 60%relative humidity.When broilers were 29-day-old,the temperature of one of the treatment regulated its temperature to 31°C while the other remained unchanged.The relative humidity in two groups was unchanged at 60%.It took 14 days to conduct the trial.The results showed that:1)The ADFI in the 31°C group showed distinctly lower than that in the 21°C group?P<0.05?,and the ADG was significantly lower in the 31°C group than in the 21°C group during 1¹4 days of the trial?P<0.05?,and the 31°C group significantly increased the F/G than that in the 21°C group?P<0.05?.2)The level of IGF-1 and AKP in serum in the 31°C group were significantly lower than that in the21°C?P<0.05?,and the 31°C group significantly reduced the expression of PTHrP protein in tibial growth plate and the tibial width?P<0.05?.The proportion of breast muscle,the expression of IGF-1mRNA and the expression of MyoD mRNA in breast muscle were distinctly lower in the 31°C group than that in the 21°C group?P<0.05?.3)The 31°C group significantly increased the content of MDA in the liver of broiler chickens?P<0.05?.4)The 31°C group significantly reduced the jejunum length,the villus height,increasing the crypt depth compared with 21°C?P<0.05?,and destroyed the intestinal structure.Conclusion:1)HSD?18.75/m²?at appropriate temperature reduced the protein expression of PTHrP in tibial growth plate,moreover,the tibial length and weight also declined.Besides,HSD reduced the mRNA expression of IGF-1 mRNA and MyoD in breast muscle and increased the mRNA expression of MSTN in breast muscle,reducing the proportion of breast muscle;2)31°C moderate temperature reduced the protein expression of PTHrP in tibial growth plate and the tibial width,and also reduced the mRNA expression of IGF-1 and MyoD in breast muscle and the proportion of breast muscle;3)in addition,both HSD and 31°C moderate temperature increased oxidative stress and caused damage to jejunum morphology.