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Abstract To analyze the causes affecting production situation of one pig farm in southwest region， group leader， assistant and related staffs in the pig farm were queried， mating and delivery situation of sow and deadculling situation ofpigletwere investigated. The results showed that ① mating situation： mating 691 pigs， returning to love 42 pigs， abortion 4 pigs， mismatching rate was 7.59%. ② Delivery situation： delivering 175nests， total birth 2538， total piglet per fetus 14.5， average healthy piglet per fetus 10.12， invalid piglet rate was30.21%. Among them， mummy fetus， dead fetus， weak piglet and deformity accounted for 47.78%， 35.64%， 10.71% and 5.87% of invalid piglet. ③ Deadculling situation： deadculling rate in breeding process was 12.37%. Among them， diarrhea death wasthemain cause， accounting for 44.47%， followed by pressing， falling to the ground， disease， joint swelling， weakness and other causes， and they respectively accounted for 18.58%， 13.36%， 13.36%， 8.56%， 5.85% and 0.62%.
Key words Pig; Mating; Abortion; Mummy fetus; Dead fetus; Feeding management procedures
One pig farm in southwest region sets production zone， living zone and auxiliary zone， and annual sow number on production line is about 4 000. Boar number is 45， and annual piglet number is about 80 000. The pig farm adopts the advanced production mode， uses centralization and largespan steel structure construction， installs automatic systems （automatic environmental control system， automatic feeding system， automatic manure cleaning system， highpressure washing system， full column system， cement slatted floor， perfect biosafety system and internet of things monitoring）， matches perfect manure disposal system and harmless treatment machine for sick pigs. According to different growth stages of pig and actual fat value， it could feed related healthy drug for pig， to further guarantee accurate breeding of pig. In different periods， it could guarantee suitable temperature and humidity for pig， to timely understand health degree of each pig. Meanwhile， mechanical manure scraping mode is used to save labor force， and automatic cooling system is used to perfect closed management， while automatic water level device is applied to realize source emission reduction.
Breeding and delivery situation of sow， deadculling situation of piglet are important indexes reflecting production management level of pig farm， while mismatch rate of estrus sows， invalid piglet rate of sows delivery and deadculling rate of piglet are important indexes measuring production performance of pig farm. Sow returning to love and abortion causing mismatch， sow delivering invalid piglet， deadculling of piglet affect production performance and economic benefit of pig farm， and hinder the development of pig industry in China. In this paper， production influence factors of the pig farm were investigated and analyzed. Due to the work needs， the field investigation of farrowing house was less， and the situation of farrowing house was mostly from the inquisition on group leader， assistant and related staff in No.1 and No.2 farrowing houses. By field investigation and referring to feed management of reserve pig， feed management of pregnant sow， feed management procedure of piglet， mating record card， delivery schedule and production record sheet， mating and delivery houses of No.1 and No.2 lines were investigated， group leader， assistant and related staff were queried， and mating and delivery situation of sow， deadculling situation of piglet were analyzed. The research aimed to decline mismatch rate of estrus sows， invalid piglet rate， deadculling rate of piglet， and further improve production performance of pig farm. Investigation method
By field investigation and referring to feed management of reserve pig， feed management of pregnant sow， feed management procedure of piglet， mating record card， delivery schedule and production record sheet， mating and delivery situation of sow， deadculling situation of piglet in the pig farm were investigated. The investigation time was from February 27 to April 7， 2018.
Investigation results
Feed management of replacement pig
Feeding
Initial feeding of the newly entered pig is a very key step. In prior three days， it should add anti stress drugs in the feed or water， such as VC. The newly entered pigswere not fed and were only provided by sufficient water. In the second meal， 1/3 of normal standard feed was fed. In the third meal， 2/3 of normal standard feed was fed. To the fourth meal， they could freely feed. The newly entered replacement pigs should be fed for three times at least every day， and feed amount of the replacement pig less than 150d old should be controlled within 2.5 kg/d.
Adjusting fence
After the replacement pigs entered mating house， they should be grouped according to fat value. Pig group was caught in corresponding fence， and corresponding sow record card was hung according to pig ear brand， to convenient for management. It should check the information of breeding herd， and establish batch immunization files， health files， estrus tracking files， breeding record files and note files of related disease.
Health and immunity
The health care of replacement pig depended on growth situation of the introduced boar. For the pig group with slow growth， rough fur， bad growth condition， and poor health condition， glucose， codliver oil， additive energy supplement， compound VB， fish meal and other nutritional additives could be added in the feed. According to health situation of boar， the optimal health care plan combining western medicine with Chinese herbal medicine was made to improve the resistance of pig group to disease. According to source of boar and disease condition， health care plan of replacement pig was made by combining seasonal characteristics， and health care plan concentrated in resisting stress， controlling respiratory disease， maintaining intestinal health， increasing feeding amount and mono nutrient， expelling parasite and improving nonspecific immunity of pig group.
In addition to this， it should do immunization plan of each batch of introduced replacement pig well， check the information of pig group before immunity， do anti stress work before and after immunity （two days before and after immunization）， and strictly implement immunity operation according to vaccine immunization program of batch boar. Promoting estrus
Estrus induction： before 160d old of replacement pig， farmyard worker took boars in the sow lane to induce estrus for twice， once in the morning and another in the afternoon， to ensure that boars and sows had enough touching time.
Promoting estrus： after 160d old of replacement pig， boars were caught to the big fence to closely touch with replacement pig. It should guarantee that boars and sows had enough close contact time.
Mating of oestrus sow
The selected sows were mated by artificial insemination， and threetime insemination method was used.
Feeding management of pregnant sow
Firstly， fat measurement and feed adjustment work should be strictly implemented， and the aim was to improve newborn weight of piglets and lactating performance of sows. At present， 4， 8 and 13 Wof fat adjustment for mating was implemented， and the feed was adjusted according to fat condition. Additionally， three stages also should be grasped.
（1）Prophase—preventing abortion and preserving fetus. It was dangerous stage in 1-4 W， and feeding should be quick， accurate and stable. Feed amount should not be lower than lower limit and higher than upper limit， and various stress should be reduced.
（2）Metaphase—5-12 W. It was fat adjustment stage， and fat mark was done. According to fat condition， feeding method was selected， to ensure that pregnant sows had rational fat condition， and feeding amount should not change， or else farrowing was uneven.
（3）Later stage—tapping. It was tapping stage in 13-16 W. It should stably feed and do health care at each stage， to guarantee that born weight of piglet and good lactation performance of sow.
Breeding management of piglets
Attendance of newly born piglets
Clean and dry towel was used to wipe mucus on mouth and nose of the newly born piglet， and wipe up the entire pig body. Umbilical cord was cut at the place 3-4 cmfromthe root， and it should not bleed in the process. 3%-5% of iodine tincture was used to sterilize umbilical cord cutting mouth to avoid infect wound. Within 24 h after delivery， 0.5 copies of pseudorabies （live vaccines） were added by nose drop， while 0.5 copies of pseudorabies were added by intramuscular injection.
Attendance in lactation
Weighing and anemia prevention work of newly born piglets should be done well within 24 h. Iron preparation could be injected to prevent piglet anemia， and teeth cutting， molars or tailcutting work also should be conducted. Castration of small boar
Incisional position of 3-5dold small boar castration should be at inferior position of scrotum midline， and cut should not be too large. The testis should be slowly pulled out， and the postoperative wound was sterilized by 5% of iodine tincture.
Attendance of weaning piglet
21d old of piglets started to wean， and VC powder， electrolyte or other medicine drinking water preventing stress was used to feed piglets. Sanzhen powder could be added in piglet feed to prevent indigestion， and 310 feed or other milk substitute and nutritive medicine could be added in the feed to enhance health condition of piglet. The weaning sow could take free feeding or proper feed control in 3 days before weaning.
Mating situation
There were 619 oestrus sows for mating， 47 sows without gestation， returning to love and miscarrying in the farm， and mismatching rate was 7.59%.
Delivery situation
In the pig farm， 175 sows delivered 2 538 piglets， and there were 766 invalid piglets. Among them， mummy fetus was main cause， accounting for 47.78% of invalid piglets， while dead fetus， weak piglet， and deformity respectively accounted for 35.64%， 10.71%， and 5.87% （Fig.1）.
Deadculling situation
In breeding process， there were 479 deadculling piglets， in which diarrhea was main cause， accounting for 44.47%. Pressing， falling to the ground， disease， arthrocele， weakness and other causes respectively accounted for 18.58%， 13.36%， 8.56%， 8.56%， 5.85% and 0.62% （Fig.2）.
Agricultural Biotechnology2018
Analysis and discussion
During the investigation period， mismatching rate of the sow in the farm was 7.59%. The mated sows returned to love and miscarried， which may be caused by improper feeding and management. For example， in fence adjustment process， when there was water on the ground， it could make sows fall to the ground， and whipping， frightening and catching were all easy to cause sow abortion[1]. Too fat or thin sow， too early mating age， highly inbreeding and endocrine system disorders all could cause worse fetus growth， activity decline and sow abortion[2]. Oestrus symptoms of individual pig was not obvious， and the breeder was negligent， causing late insemination. Ovum arranged by sow could not combine with sperm and then aged， and sow was infertile， causing it returned to love[3]. When sows suffered from localized hystertis， congenital endometritis and colpitis， it could make that fetus growth was limited. If there was no timely therapy， it could cause that the internal environment of fetal development was blocked， inducing abortion[4]. The research results showed that invalid piglet rate in the farm was 30.21%， which was higher. Among them， mummy may be caused by breeding management in prior 90 days of pregnancy. There were very complicated causes for sow delivering mummy， dead fetus， weak piglet and deformity， containing genetic factor and breeding management， but it was mainly induced by pathogenic microbes[5]. Most of dead fetus was caused by dystocia， and longer delivery process caused fetus death[6]. Dead fetus and mummy fetus were related to environmental temperature， number and size of the newly born piglet[7]. There were more complicated causes for dead fetus， containing reproduction， management， feed， environment and disease[8]. Parturition malformation may be induced by inheritance and inbreeding， causing prolonged pregnancy， fetal malformation and dystocia， and weak activity[9]. The causes inducing the pregnant sows to deliver mummy， dead fetus， weak piglet and deformity were complex， which could be divided into disease， nutrient， environment and inheritance[10]. Therefore， it could effectively reduce invalid piglet rate by strictly valuing breeding management of pregnant pig.
It was found that there was serious deadculling situation in breeding process. Among them， diarrhea accounted for 44.47%， which was the largest， followed by pressing （18.58%）， falling to the ground （13.36%）， disease （8.56%）， arthrocele （8.56%）， weakness （5.85%） and other （0.62%）. The newly born piglets had underdeveloped digestive organs and imperfect function. After weaning， food change affected digestion and absorption of digesta， causing diarrhea[11]. When temperature was low， heat dissipation of piglet was higher than heat production， which was easy to suffer from cold stress. When suffering from cold stress， piglet’s body temperature quickly declined， and body energy was given priority to thermoregulation. Therefore， it lacked enough energy for organism playing immunity function， causing that its own disease resistance decreased， and daily weight increase was slow， which was one of important causes for piglet death[12]. The newly born piglet was extremely easy to fear the cold， and it should provide suitable temperature for piglet and scientific breed， which could effectively reduce its deadculling rate by diarrhea. When sow was sick， the quality and quantity of colostrum were insufficient， causing colostrum assimilated by piglet was not enough and piglet diarrhea[13]. Body temperature decline of the newly born piglet also could cause weak constitution and gray matter necrosis of cerebral cortex[13]. Pig is one of animals without maternal instinct in mammals， which does not change by domestication， and the phenomenon of piglet pressed generally exists[14]. Therefore， it should strictly value temperature and breeding management of delivery room and enhance nursing work of the breeder. References
[1] ZHANG HT， JIN TF， HUANG ST， et al. Cause analysis of sow abortion and its control countermeasures[J]. Jilin Animal Science and Veterinary Medicine，2009，30（8）： 23. （in Chinese）.
[2] XU D， LIU W， LI HJ， et al. Fat control and its application in improving reproductive performance of sows[J]. Shanghai Journal of Animal Husbandry and Veterinary Medicine， 2012（5）：54-55. （in Chinese）.
[3] YAN DH. Cause and countermeasure of sows returning to love and abortion in largescale pig farm[J]. Northern Pasture， 2009（9）： 16. （in Chinese）.
[4] ZHU JB， ZHANG SQ， CHEN YM， et al. Controlling obstetric diseases of sows and improving reproductive potential of sows——common causes and control of sow abortion[J]. Swine Industry Science， 2010（8）：28-31. （in Chinese）.
[5] ZHENG YC， LIN ZJ. Cause for sow abortion and dead fetus in largescale pig farm and control measures[J].Livestock and Poultry Industry，2011（1）：76. （in Chinese）.
[6] CHRISTIANSON WT. Stillbirths， mummies， abortions， and early embryonic death[J].Vet Clin North Am Exot Anim Pract，1992，8（3）：623.
[7] SHA RN， JIA Q， LIU HJ， et al. Logistic regression analysis of stillbirth and mummy in sow[J]. Ani Husb & Vet Med， 2009，41（10）：17-21.
[8] CHENG ZG， DING FY. Cause analysis of breeding sows producing more dead fetuses and defense measures[J].Pigs Today，2012（1）： 40-43. （in Chinese）.
[9] ZHAO XX. Veterinary obstetrics （the fourth version）[M]. Beijing： China Agriculture Press， 2008. （in Chinese）.
[10] LI J. Several factors inducing sows delivering mummy， dead fetus and weak piglet[J]. Livestock and Poultry Industry， 2013（5）：51-52. （in Chinese）.
[11] ZHOU HG. Causes of piglet diarrhea and control[J].Animals Breeding and Feed， 2003（8）：39-41. （in Chinese）.
[12] RYDHMER L， LUNDEHEIM N， CANARIO L.Genetic correlations between gestation length， piglet survival and early growth[J]. Livestock Sci，2008，115（2-3）：287-293.
[13] SHEN RL. Exploration on piglet diarrhea cause[J]. Shanghai Journal of Animal Husbandry and Veterinary Medicine，2000（1）：29.（in Chinese）.
[14] GUSTAFSSON M， JENSEN P， JONGE FHD， et al. Maternal behaviour of domestic sows and crosses between domestic sows and wild boar[J]. Appl Anim Behav Sci，1999， 65（1）：29-42.
Key words Pig; Mating; Abortion; Mummy fetus; Dead fetus; Feeding management procedures
One pig farm in southwest region sets production zone， living zone and auxiliary zone， and annual sow number on production line is about 4 000. Boar number is 45， and annual piglet number is about 80 000. The pig farm adopts the advanced production mode， uses centralization and largespan steel structure construction， installs automatic systems （automatic environmental control system， automatic feeding system， automatic manure cleaning system， highpressure washing system， full column system， cement slatted floor， perfect biosafety system and internet of things monitoring）， matches perfect manure disposal system and harmless treatment machine for sick pigs. According to different growth stages of pig and actual fat value， it could feed related healthy drug for pig， to further guarantee accurate breeding of pig. In different periods， it could guarantee suitable temperature and humidity for pig， to timely understand health degree of each pig. Meanwhile， mechanical manure scraping mode is used to save labor force， and automatic cooling system is used to perfect closed management， while automatic water level device is applied to realize source emission reduction.
Breeding and delivery situation of sow， deadculling situation of piglet are important indexes reflecting production management level of pig farm， while mismatch rate of estrus sows， invalid piglet rate of sows delivery and deadculling rate of piglet are important indexes measuring production performance of pig farm. Sow returning to love and abortion causing mismatch， sow delivering invalid piglet， deadculling of piglet affect production performance and economic benefit of pig farm， and hinder the development of pig industry in China. In this paper， production influence factors of the pig farm were investigated and analyzed. Due to the work needs， the field investigation of farrowing house was less， and the situation of farrowing house was mostly from the inquisition on group leader， assistant and related staff in No.1 and No.2 farrowing houses. By field investigation and referring to feed management of reserve pig， feed management of pregnant sow， feed management procedure of piglet， mating record card， delivery schedule and production record sheet， mating and delivery houses of No.1 and No.2 lines were investigated， group leader， assistant and related staff were queried， and mating and delivery situation of sow， deadculling situation of piglet were analyzed. The research aimed to decline mismatch rate of estrus sows， invalid piglet rate， deadculling rate of piglet， and further improve production performance of pig farm. Investigation method
By field investigation and referring to feed management of reserve pig， feed management of pregnant sow， feed management procedure of piglet， mating record card， delivery schedule and production record sheet， mating and delivery situation of sow， deadculling situation of piglet in the pig farm were investigated. The investigation time was from February 27 to April 7， 2018.
Investigation results
Feed management of replacement pig
Feeding
Initial feeding of the newly entered pig is a very key step. In prior three days， it should add anti stress drugs in the feed or water， such as VC. The newly entered pigswere not fed and were only provided by sufficient water. In the second meal， 1/3 of normal standard feed was fed. In the third meal， 2/3 of normal standard feed was fed. To the fourth meal， they could freely feed. The newly entered replacement pigs should be fed for three times at least every day， and feed amount of the replacement pig less than 150d old should be controlled within 2.5 kg/d.
Adjusting fence
After the replacement pigs entered mating house， they should be grouped according to fat value. Pig group was caught in corresponding fence， and corresponding sow record card was hung according to pig ear brand， to convenient for management. It should check the information of breeding herd， and establish batch immunization files， health files， estrus tracking files， breeding record files and note files of related disease.
Health and immunity
The health care of replacement pig depended on growth situation of the introduced boar. For the pig group with slow growth， rough fur， bad growth condition， and poor health condition， glucose， codliver oil， additive energy supplement， compound VB， fish meal and other nutritional additives could be added in the feed. According to health situation of boar， the optimal health care plan combining western medicine with Chinese herbal medicine was made to improve the resistance of pig group to disease. According to source of boar and disease condition， health care plan of replacement pig was made by combining seasonal characteristics， and health care plan concentrated in resisting stress， controlling respiratory disease， maintaining intestinal health， increasing feeding amount and mono nutrient， expelling parasite and improving nonspecific immunity of pig group.
In addition to this， it should do immunization plan of each batch of introduced replacement pig well， check the information of pig group before immunity， do anti stress work before and after immunity （two days before and after immunization）， and strictly implement immunity operation according to vaccine immunization program of batch boar. Promoting estrus
Estrus induction： before 160d old of replacement pig， farmyard worker took boars in the sow lane to induce estrus for twice， once in the morning and another in the afternoon， to ensure that boars and sows had enough touching time.
Promoting estrus： after 160d old of replacement pig， boars were caught to the big fence to closely touch with replacement pig. It should guarantee that boars and sows had enough close contact time.
Mating of oestrus sow
The selected sows were mated by artificial insemination， and threetime insemination method was used.
Feeding management of pregnant sow
Firstly， fat measurement and feed adjustment work should be strictly implemented， and the aim was to improve newborn weight of piglets and lactating performance of sows. At present， 4， 8 and 13 Wof fat adjustment for mating was implemented， and the feed was adjusted according to fat condition. Additionally， three stages also should be grasped.
（1）Prophase—preventing abortion and preserving fetus. It was dangerous stage in 1-4 W， and feeding should be quick， accurate and stable. Feed amount should not be lower than lower limit and higher than upper limit， and various stress should be reduced.
（2）Metaphase—5-12 W. It was fat adjustment stage， and fat mark was done. According to fat condition， feeding method was selected， to ensure that pregnant sows had rational fat condition， and feeding amount should not change， or else farrowing was uneven.
（3）Later stage—tapping. It was tapping stage in 13-16 W. It should stably feed and do health care at each stage， to guarantee that born weight of piglet and good lactation performance of sow.
Breeding management of piglets
Attendance of newly born piglets
Clean and dry towel was used to wipe mucus on mouth and nose of the newly born piglet， and wipe up the entire pig body. Umbilical cord was cut at the place 3-4 cmfromthe root， and it should not bleed in the process. 3%-5% of iodine tincture was used to sterilize umbilical cord cutting mouth to avoid infect wound. Within 24 h after delivery， 0.5 copies of pseudorabies （live vaccines） were added by nose drop， while 0.5 copies of pseudorabies were added by intramuscular injection.
Attendance in lactation
Weighing and anemia prevention work of newly born piglets should be done well within 24 h. Iron preparation could be injected to prevent piglet anemia， and teeth cutting， molars or tailcutting work also should be conducted. Castration of small boar
Incisional position of 3-5dold small boar castration should be at inferior position of scrotum midline， and cut should not be too large. The testis should be slowly pulled out， and the postoperative wound was sterilized by 5% of iodine tincture.
Attendance of weaning piglet
21d old of piglets started to wean， and VC powder， electrolyte or other medicine drinking water preventing stress was used to feed piglets. Sanzhen powder could be added in piglet feed to prevent indigestion， and 310 feed or other milk substitute and nutritive medicine could be added in the feed to enhance health condition of piglet. The weaning sow could take free feeding or proper feed control in 3 days before weaning.
Mating situation
There were 619 oestrus sows for mating， 47 sows without gestation， returning to love and miscarrying in the farm， and mismatching rate was 7.59%.
Delivery situation
In the pig farm， 175 sows delivered 2 538 piglets， and there were 766 invalid piglets. Among them， mummy fetus was main cause， accounting for 47.78% of invalid piglets， while dead fetus， weak piglet， and deformity respectively accounted for 35.64%， 10.71%， and 5.87% （Fig.1）.
Deadculling situation
In breeding process， there were 479 deadculling piglets， in which diarrhea was main cause， accounting for 44.47%. Pressing， falling to the ground， disease， arthrocele， weakness and other causes respectively accounted for 18.58%， 13.36%， 8.56%， 8.56%， 5.85% and 0.62% （Fig.2）.
Agricultural Biotechnology2018
Analysis and discussion
During the investigation period， mismatching rate of the sow in the farm was 7.59%. The mated sows returned to love and miscarried， which may be caused by improper feeding and management. For example， in fence adjustment process， when there was water on the ground， it could make sows fall to the ground， and whipping， frightening and catching were all easy to cause sow abortion[1]. Too fat or thin sow， too early mating age， highly inbreeding and endocrine system disorders all could cause worse fetus growth， activity decline and sow abortion[2]. Oestrus symptoms of individual pig was not obvious， and the breeder was negligent， causing late insemination. Ovum arranged by sow could not combine with sperm and then aged， and sow was infertile， causing it returned to love[3]. When sows suffered from localized hystertis， congenital endometritis and colpitis， it could make that fetus growth was limited. If there was no timely therapy， it could cause that the internal environment of fetal development was blocked， inducing abortion[4]. The research results showed that invalid piglet rate in the farm was 30.21%， which was higher. Among them， mummy may be caused by breeding management in prior 90 days of pregnancy. There were very complicated causes for sow delivering mummy， dead fetus， weak piglet and deformity， containing genetic factor and breeding management， but it was mainly induced by pathogenic microbes[5]. Most of dead fetus was caused by dystocia， and longer delivery process caused fetus death[6]. Dead fetus and mummy fetus were related to environmental temperature， number and size of the newly born piglet[7]. There were more complicated causes for dead fetus， containing reproduction， management， feed， environment and disease[8]. Parturition malformation may be induced by inheritance and inbreeding， causing prolonged pregnancy， fetal malformation and dystocia， and weak activity[9]. The causes inducing the pregnant sows to deliver mummy， dead fetus， weak piglet and deformity were complex， which could be divided into disease， nutrient， environment and inheritance[10]. Therefore， it could effectively reduce invalid piglet rate by strictly valuing breeding management of pregnant pig.
It was found that there was serious deadculling situation in breeding process. Among them， diarrhea accounted for 44.47%， which was the largest， followed by pressing （18.58%）， falling to the ground （13.36%）， disease （8.56%）， arthrocele （8.56%）， weakness （5.85%） and other （0.62%）. The newly born piglets had underdeveloped digestive organs and imperfect function. After weaning， food change affected digestion and absorption of digesta， causing diarrhea[11]. When temperature was low， heat dissipation of piglet was higher than heat production， which was easy to suffer from cold stress. When suffering from cold stress， piglet’s body temperature quickly declined， and body energy was given priority to thermoregulation. Therefore， it lacked enough energy for organism playing immunity function， causing that its own disease resistance decreased， and daily weight increase was slow， which was one of important causes for piglet death[12]. The newly born piglet was extremely easy to fear the cold， and it should provide suitable temperature for piglet and scientific breed， which could effectively reduce its deadculling rate by diarrhea. When sow was sick， the quality and quantity of colostrum were insufficient， causing colostrum assimilated by piglet was not enough and piglet diarrhea[13]. Body temperature decline of the newly born piglet also could cause weak constitution and gray matter necrosis of cerebral cortex[13]. Pig is one of animals without maternal instinct in mammals， which does not change by domestication， and the phenomenon of piglet pressed generally exists[14]. Therefore， it should strictly value temperature and breeding management of delivery room and enhance nursing work of the breeder. References
[1] ZHANG HT， JIN TF， HUANG ST， et al. Cause analysis of sow abortion and its control countermeasures[J]. Jilin Animal Science and Veterinary Medicine，2009，30（8）： 23. （in Chinese）.
[2] XU D， LIU W， LI HJ， et al. Fat control and its application in improving reproductive performance of sows[J]. Shanghai Journal of Animal Husbandry and Veterinary Medicine， 2012（5）：54-55. （in Chinese）.
[3] YAN DH. Cause and countermeasure of sows returning to love and abortion in largescale pig farm[J]. Northern Pasture， 2009（9）： 16. （in Chinese）.
[4] ZHU JB， ZHANG SQ， CHEN YM， et al. Controlling obstetric diseases of sows and improving reproductive potential of sows——common causes and control of sow abortion[J]. Swine Industry Science， 2010（8）：28-31. （in Chinese）.
[5] ZHENG YC， LIN ZJ. Cause for sow abortion and dead fetus in largescale pig farm and control measures[J].Livestock and Poultry Industry，2011（1）：76. （in Chinese）.
[6] CHRISTIANSON WT. Stillbirths， mummies， abortions， and early embryonic death[J].Vet Clin North Am Exot Anim Pract，1992，8（3）：623.
[7] SHA RN， JIA Q， LIU HJ， et al. Logistic regression analysis of stillbirth and mummy in sow[J]. Ani Husb & Vet Med， 2009，41（10）：17-21.
[8] CHENG ZG， DING FY. Cause analysis of breeding sows producing more dead fetuses and defense measures[J].Pigs Today，2012（1）： 40-43. （in Chinese）.
[9] ZHAO XX. Veterinary obstetrics （the fourth version）[M]. Beijing： China Agriculture Press， 2008. （in Chinese）.
[10] LI J. Several factors inducing sows delivering mummy， dead fetus and weak piglet[J]. Livestock and Poultry Industry， 2013（5）：51-52. （in Chinese）.
[11] ZHOU HG. Causes of piglet diarrhea and control[J].Animals Breeding and Feed， 2003（8）：39-41. （in Chinese）.
[12] RYDHMER L， LUNDEHEIM N， CANARIO L.Genetic correlations between gestation length， piglet survival and early growth[J]. Livestock Sci，2008，115（2-3）：287-293.
[13] SHEN RL. Exploration on piglet diarrhea cause[J]. Shanghai Journal of Animal Husbandry and Veterinary Medicine，2000（1）：29.（in Chinese）.
[14] GUSTAFSSON M， JENSEN P， JONGE FHD， et al. Maternal behaviour of domestic sows and crosses between domestic sows and wild boar[J]. Appl Anim Behav Sci，1999， 65（1）：29-42.