Effects Of Different Social Contact Models During Lactation On Behaviors And Intestinal Health Of Piglet

The enriched social environment during lactation can reduce the aggressive behavior of piglets,which improves the production performance and welfare of piglets.The aim of this study was to investigate the effects of the different social contact models during lactation on the aggressive behavior and fecal microbiota of piglets.Thirty litters of crossbred piglets(Large white × Duroc ×Min pig)were randomly divided into three groups: control group(CON),intermittent social contact group(ISC),and continuous social contact group(CSC).There were 6 litters of piglets in the CON group,and the piglets were raised in farrowing pens from birth to 35 days of age.There was no social contact between the two adjacent litters during lactation in the CON group.There were 12 litters of piglets in the ISC group,and the fence between every two adjacent litters was removed from 13:00 to 16:00 at 14,15,21,22,28,29,33,and 34 days of age,during which the piglets from the adjacent litters were allowed to contact each other freely.There were also 12 litters of the piglets in the CSC group,the fence was removed from 14 days of age to 35 days of age,and the piglets from two adjacent litters were allowed to contact freely at any time during this period.All piglets were weaned at 35 days of age.At 35 days of age,the piglets in each group were regrouped into six weaned pens with 10 piglets per pen based on bodyweight and gender.Behaviors(standing,lying,walking,and aggressive behaviors)during lactation(2,3,4,and 5 weeks of age)and growing period(6,7,8,and 9 weeks of age)and aggressive behaviors in 70 hours after weaned were observed to investigate the effect of social contact models on the piglets.The physiological markers including cortisol,norepinephrine,adrenocorticotropic hormone(ACTH),epinephrine,and Pig-MAP and immune parameters including interferon-γ(IFN-γ),tumor necrosis factor-α(TNF-α),interleukin-1β(IL-1β),IL-6,IL-8,IL-10,toll-like receptor 2(TLR2),immune globulin A(Ig A),and Ig G in serum were detected at 16,35,42,and 63 days of age.The concentrations of brain-gut peptides including serotonin(5-HT),substance P,corticotropin-releasing factor(CRF),and growth hormone-releasing peptide and oxytocin were measured at 35 and 63 days of age.The fecal samples were collected at16,35,42,and 63 days of age and performed 16 S r RNA gene sequencing.At 35 and 63 days of age,six female piglets were euthanized randomly in each group,and the ileac mucosa,colonic mucosa,hypothalamus,ventral prefrontal cortex,hippocampus,and amygdala were collected for the determination of mucosal barrier-related genes and protein in ileac and colonic mucosa were detected by real-time quantitative PCR(q RT-PCR)and western blot,respectively.The HPA axis and nerve growth-related genes in the hypothalamus,ventral prefrontal cortex,hippocampus,and amygdala at 35 and 63 days of age were detected by q RT-PCR.Besides,the transcriptome analysis of the hypothalamus at 63 days of age was performed.The results showed that:(1)The different social contact models changed the behaviors of suckling-growing piglets.During lactation,the piglets in the ISC and CSC groups had more walking and standing behaviors and less lying behavior than those in the CON group(P < 0.05).During the growing period,compared with the CON group,the ISC piglets had more lying behavior(P < 0.05),and the CSC piglets had less lying behavior(P < 0.05).Thus,the piglets with enriched social contact during lactation were more active.(2)During lactation,aggressive behavior was significantly decreased in the ISC,CSC,and CON groups in turn(P < 0.05).During the growing period,aggressive behavior was significantly decreased in the CON,CSC,and ISC groups in turn(P < 0.05).The social contact models during lactation can reduce the aggressive behavior of piglets during the growing period.(3)The results of fecal 16 S r DNA gene sequencing showed that at the end of the growing period,compared with the CON group,the abundance of beneficial microorganisms(Bifidobacterium and Prevotella＿9,etc.)was significantly increased in the ISC group,the abundance of harmful microorganisms(Desulfovibrio and Pseudomonas,etc.)was significantly increased in the CSC group.The litter weight of piglets in the CON and ISC groups was significantly higher than that in the CSC group(P < 0.05).(4)The results of intestinal microstructure showed that the ileac lamina propria was exposed at 35 days of age in the CSC group,the ileac gland spacing was wider and a few epithelial cells were shed in the ileac epithelium at 63 days of age in the CON group,the remaining ileac and colonic structures were relatively intact without obvious inflammation.The chromatin of the ileum and colon at 35 days of age in the CON,ISC,and CSC groups had a small amount of agglutination,marginalization,and nuclear deformation.At 63 days of age,only the ileac and colonic ultrastructures in the ISC group were normal with completed and clear nuclear structure,while CON and CSC groups had a small amount of chromatin agglutination and nuclear deformation.(5)The results of intestinal mucosal barrier-related genes showed that compared with the CON group,ISC inhibited m RNA expression of Claudin-4 and Claudin-5 in ileac mucosa and MUC2 in colonic mucosa(P < 0.05),and promoted m RNA expression of Claudin-1 and Claudin-8 in ileac mucosa(P < 0.05);CSC inhibited m RNA expression of Claudin-1,Claudin-4,Claudin-5 and Claudin-12 in ileac mucosa(P < 0.05),and promoted m RNA expression of Claudin-3 in ileac mucosa and Claudin-2,Claudin-3,ZO-2,and MUC1 in colonic mucosa at 35 days of age(P < 0.05).At 63 days of age,the expression of Claudin-5,Claudin-10,Claudin-12,and Occludin m RNA in ileac mucosa in the ISC group was lower than that in the CON group(P < 0.05),while the expression levels of Claudin-1,ZO-1,MUC1 and MUC2 m RNA in ileac mucosa and Claudin-1,Claudin-3,Claudin-5,Claudin-8 and ZO-1 m RNA in colonic mucosa were higher than that in the CON group(P < 0.05);m RNA expression of Claudin-5,Claudin-10,and Claudin-12 in ileac mucosa of CSC group was lower than that of CON group(P < 0.05),while the expression levels of Claudin-1,Claudin-7,ZO-1,MUC1 and MUC2 in ileac mucosa and colonic mucosa were higher than those in CON group(P < 0.05).(6)The result of intestinal barrier-related proteins showed that ISC inhibited Occludin expression(P < 0.05);CSC promoted the expression of Occludin and ZO-1 protein in ileac mucosa(P < 0.05),and inhibited the expression of Occludin and ZO-1 in colonic mucosa at 35 days of age(P < 0.05).At 63 days of age,ISC promoted Claudin-1 expression in ileac mucosa and ZO-1 protein expression in colonic mucosa(P < 0.05);CSC inhibited the expression of ZO-1 proteins in ileum mucosa,and Claudin-1 and ZO-1 proteins in colonic mucosa(P < 0.05)and promoted the expression of Claudin-1 in ileac mucosa(P < 0.05).(7)The results of inflammation-related genes expression showed that the m RNA levels of IL-2,IL-6,IL-17,TNF-α,and IFN-γ in ileac mucosa of the ISC group were significantly lower than those in the CON group at 35 days of age(P < 0.05),but m RNA expression of IL-8 in ileac mucosa and IL-2 in colonic mucosa was significantly higher than that in CON group(P < 0.05);m RNA expression of TLR4,IL-1β,IL-2,IL-6,IL-17 and TNF-α in ileac mucosa of CSC group was significantly lower than those in CON group(P < 0.05),but m RNA expression levels of IL-8 in ileac mucosa and TLR5,IL-1β,IL-8 and IFN-γ in colonic mucosa were significantly higher than those in CON group(P < 0.05)at 35 days of age.At 63 days of age,ISC inhibited m RNA expression of IL-8 and IL-17 in ileac mucosa as well as IL-8 and TNF-α in colonic mucosa compared with the CON group(P < 0.05),promoted the expression of TLR2,TLR4,TLR5,TLR7,IL-2 and IL-6 in ileac mucosa and IL-6 in colonic mucosa(P < 0.05);CSC inhibited m RNA expression of IL-8 and IL-17 in ileac mucosa(P < 0.05),promoted m RNA expression of TLR2,TLR5,IL-1β,IL-2,IL-6and IFN-γ in ileac mucosa and IL-2,IL-17 and IFN-γ in colonic mucosa(P < 0.05).(8)At 16,35,42,and 63 days of age,there was no significant difference in the levels of ACTH,epinephrine,and norepinephrine in serum among CON,ISC,and CSC groups(P > 0.05).Compared with the CON group,the content of cortisol in serum in the ISC group was significantly decreased at 16 and 42 days of age(P < 0.05),and that in the CSC group was significantly increased at 35 days of age(P < 0.05)and significantly decreased at 63 days of age(P < 0.05).Compared to the CON group,ISC inhibited the expression of oxytocin receptor(OXTR)and mineralocorticoid receptors(MR)m RNA in the hypothalamus of piglets at 63 days of age(P < 0.05),and promoted OXTR m RNA expression in the ventral prefrontal cortex and hippocampus of piglets at 35 days of age and in the hippocampus at 63 days of age(P < 0.05);CSC inhibited MR m RNA expression in the hypothalamus and amygdala of piglets at 35 and 63 days of age(P < 0.05),and promoted the m RNA expression of OXTR in the ventral prefrontal cortex,hippocampus,and amygdala at 35 days of age and in the ventral prefrontal cortex and hippocampus at 63 days of age(P < 0.05).(9)Transcriptome sequencing of the hypothalamus showed that compared with the CON group,563 genes were up-regulated and 463 genes were down-regulated in the ISC group,491 genes were up-regulated and 410 genes were down-regulated in the CSC group.The enrichment analysis of the Kyoto encyclopedia of genes and genomes(KEGG)pathway showed that the main differential pathways between the CON group and ISC group were cholinergic synapse,glutamatergic synapse,GABAergic synapse,dopaminergic synapse,and serotonergic synapse,while the main differential pathways between CON group and CSC group were glutamatergic synapses,GABAergic synapses,and dopaminergic synapses.In conclusion,social contact during lactation reduced aggressive behavior and changed the fecal microbial composition and intestinal mucosal barrier function of piglets during the growing period.In addition,social contact during lactation may reduce the aggressive behavior of piglets by altering brain neuroplasticity.