Effects Of Stocking Density On Rearing Environment And Growth Performance,Serum Biochemistry Indices Of Growing Pigs In Summer And Winter

Stocking density refers to the pen area occupied by each pig,usually expressed as“m²/head”,which is directly related to the cost of production,profit,physiological status of the herd,and breeding methods.This article studies the effects of stocking density on rearing environment,growth performance,antioxidant function and immune function of growing pigs in winter and summer,in order to provide a reference for the healthy breeding of pigs in southern China.ExperimentⅠ:This experiment was conducted to study the effects of stocking density on growth performance,serum biochemistry,antioxidant,immune and stress indicators of growing pigs in summer.A total of 216 healthy with similar age Large White×Landrace（LY）growing pigs with a similar initial weight of（24.64±0.13）kg were randomly divided into 4groups with 6 replicates（pens）in each group.Stocking density for the four groups were modified by varying the number of pigs per pen（6,8,10 and 12 pigs in GroupⅠ,GroupⅡ,GroupⅢand GroupⅣ,respectively）,the stocking densities of the 4 groups were 1.52,1.14,0.91 and 0.76 m² per head.The experiment period was 28 days.The results showed that:1)With the stocking density increasing,the temperature and humidity was increased.With the increase of stocking density,the concentrations of CO₂ and NH₃ was gradually increased,and the environmental concentrations of CO₂ and NH₃ in groupⅣwere significantly higher than those in groupⅠ,GroupⅡ,GroupⅢ（P<0.05）.2)With the stocking density increasing,the average daily feed intake（ADFI）and average daily gain（ADG）of growing pigs showed a linear decrease（P<0.05）.The ratio of feed to gain（F/G）of growing pigs increased linearly（P<0.05）.And there were no significant differences in ADFI,ADG and F/G between groupⅠand groupⅡ（P>0.05）.3)With the stocking density increasing,serum globulin（GLB）and thyroid hormone（T3,T4）concentrations decreased linearly（P<0.05）.Serum glucose（GLU）and low density lipoprotein（LDL）concentrations increased linearly（P<0.05）.and there were no significant differences in serum T3,T4,GLB and GLU concentrations between groupⅠand groupⅡ（P>0.05）.4)Compared with groupⅡ,serum IgA and IgG concentrations in groupⅣwere significantly lower（P<0.05）.With the stocking density increasing,the concentration of serum interleukin-1β（IL-1β）and interleukin-6（IL-6）increased linearly（P<0.05）.And there were no significant differences in serum IgA,IgG and IL-1βbetween groupⅠand groupⅡ（P>0.05）.5)With the stocking density increasing,the serum catalase（CAT）,superoxide dismutase（SOD）activity,malondialdehyde（MDA）concentration was linearly changing（P<0.05）,the total antioxidant capacity（T-AOC）presented a quadratic curve change（P<0.05）.And there were no significant differences in serum CAT,SOD activity,T-AOC and MDA concentrations between groupⅠand groupⅡ（P>0.05）.6)With the stocking density increasing,the serum ACTH concentration in groupⅣwas significantly higher than that in groupⅡandⅢ（P<0.05）,and the serum COR concentration had a increasing trend（0.05≤P<0.10）.ExperimentⅡ:This experiment was conducted to study the effects of stocking density on rearing environment and growth performance,serum biochemistry indices of growing pigs in winter.A total of 330 healthy with similar age and initial weight of（25.67±0.25）kg Large White×Landrace（LY）growing pigs were randomly divided into 4 groups with 6replicates（pens）in each group.Stocking density of the four groups were modified by varying the number of pigs per pen（10,12,15 and 18 pigs in GroupⅠ,GroupⅡ,GroupⅢand GroupⅣ,respectively）,and the stocking densities of the 4 groups were 0.91,0.76,0.61and 0.51 m² per pig.The experiment lasted for 28 days.The results showed as follows:1)With the stocking density increasing,the temperature and humidity had an increasing trend.The concentration of carbon dioxide（CO₂）and ammonia（NH₃）in the pen increased gradually with the stocking density increasing.At the 14 d,and 21 d of the experiment,the environmental CO₂ and NH₃ concentration of groupⅣwas significantly higher than other treatments（P<0.05）.2)With the stocking density increasing,the average daily feed intake（ADFI）of growing pigs was linearly decreased（P<0.05）,and the average daily gain（ADG）and ratio feed to gain（F/G）were presented a quadratic curve change（P<0.05）.The F/G in groupⅢwas significantly lower than other treatments（P<0.05）.3)With the stocking density increasing,the concentration of serum triiodothyronine（T₃）and thyroxine（T₄）were decreased linearly（P<0.05）.4)With the stocking density increasing,the serum immunoglobulin A（IgA）and immunoglobulin G（IgG）concentrations presented a quadratic curve change（P<0.05）,and the concentration of immunoglobulin M（IgM）was changed linearly（P<0.05）.The serum IgA,IgG,IgM concentrations in groupⅠwere significantly lower than groupⅡ（P<0.05）.With the stocking density increasing,the serum tumor necrosis factor（TNF-α）concentration presented a quadratic change（P<0.05）,and the serum TNF-αconcentration in groupⅡand groupⅢwas the lowest.5)Compared with groupⅢ,the groupⅠserum catalase（CAT）and glutathione peroxidase（GSH-Px）activity,total antioxidant capacity（T-AOC）concentration were significantly decreased（P<0.05）.With the stocking density increasing,the serum malondialdehyde（MDA）concentration presented a quadratic change（P<0.05）.Compared with groupⅠ,groupⅡand groupⅣ,the serum MDA concentration in groupⅢwas lowest（P<0.05）.6)The serum adrenocortical hormone（ACTH）and cortisol（COR）concentrations decreased first and then increased with stocking density increasing.There were no significant differences of serum ACTH and COR concentrations between groupⅡand groupⅢ（P>0.05）.In summary,appropriately reducing the stocking density in summer and appropriately increasing the stocking density in winter can promote the growth of pigs,improve the growth performance of the herd,immunity and antioxidant capacity of the herd,and reduce the stress level of the body.The suitable stocking density parameter for growing pig（25～45kg）is 1.14 m²/head in summer,and the suitable stocking density parameter for growing pigs is 0.61 m²/head in winter.