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Abstract Not so much attention has been paid to animal welfare in many pig farms in China yet and there are still some violations of Animal Welfare Practices. Breeding boar is the core of modern pig farm， which is responsible for the reproductive task of supplying sperm for sows. With the development of artificial insemination， breeding boar plays an increasingly important role in pig production and the welfare of it is becoming more and more important. The problems existing in the welfare of breeding boar in China scale pig farm were analyzed from the aspects of rearing method， feed， environment condition， exercise， artificial semen collection， sexual behavior and environment enrichment and the corresponding measures or countermeasures were put forwards to improve their welfare level.
Key words Animal welfare； Boar welfare； China
With the rapid development of swine industry， intensive and scale is gradually replacing the extensive and scattered farming model. Scale farming can increase productivity but is likely to harm the welfare of pigs. Animal husbandry developed countries attach great importance to the welfare of animals， but many pig farms in China， including some large farms， do not pay enough attention to animal welfare. Breeding boar is the core of modern pig farm， which is responsible for the reproductive task of supplying sperm for sows， and its quality has an important influence on the whole pig farm. With the development of artificial insemination， breeding boar plays an increasingly important role in pig production and the welfare of it is becoming more and more important. The present raising management methods should be improved to enhance the welfare level of pigs according to its physiological and psychological demands， so as to achieve the win-win situation between human beings and animals.
About Animal Welfare
So far， there is no precise definition of animal welfare. But it is generally understood that animals enjoy the five freedoms （Freedom from hunger and thirst； Freedom from discomfort； Freedom from pain， injury or disease； Freedom to express normal behavior； Freedom from fear and distress）. At present， there are still some people who do not accepted or recognize animal welfare， think that animals should not enjoy welfare. Some people advocate that animals should be equal to human beings and that animals should be totally banned even from conducting scientific experiments and that animal product should not be used by human beings. The welfare of pigs is closely related to human interests. Welfare of Breeding Boars in China
Rearing mode
Adult boars are raised in a single pen and kept away from sows in order to be in a quiet state and reduce interference， fight and hip climbing. Boars are usually kept in captivity alone， but if boars grow up together and have plenty of room to avoid fighting， they can be farmed in groups[1]. At present， for the convenience of management and cost saving， some pig farms in our country also use individual stall system for breeding boars， sometimes close to sows， or even placed in the same shed. There were no significant changes in sperm yield， sperm density and sperm motility in boars， but there were significant increase in leg and hoof injury and decrease of sexual desire after 16 months of use in boars[2]， which resulted in high rejection rate of breeding boars （generally used for less than 18 months， sperm motility could not meet the requirements and had to be eliminated）. Individual stall system is introduced from the West， mainly used for pregnant sows. It limits the free movement of pigs， and causes a series of problems， such as the long-term hog hanging in the limit column， rigid behavior， decreased cardiopulmonary function， foot and limb disease and increased mastitis and so on， and abnormal rejection rate is over 13%[3]. The limit bar not only damages the welfare of boar， but also shortens the utilization time of breeding boar. EU countries， New Zealand， Australia and other developed countries have banned or partially banned the use of individual stall， China has not banned the system. Our country stipulates that the boar pen should be allowed to turn around freely， with a minimum total area of not less than 7.5 m2/head， and a mating fence area of not less than 12 m2， so as to ensure sufficient space for courtship and mating[4]. Do not use the normal pregnancy individual stall to raise breeding boars，but use larger boar pen.
Feed
Pigs are vegetarian omnivorous animals whose ancestors feed on wild herbs and root tubers. The modern factory cultivation mode has deprived the pig of the taste of the green feed， so that it can eat complete feed for the whole life and can hardly eat green feed. Green feed can not only provide natural vitamins to pigs， but also provide dietary cellulose， which can effectively prevent constipation and play an active role in maintaining intestinal microbial balance. In addition， green feed can also increase the feeling of fullness. The multivitamins contained in green feed have a positive effect on the semen quality of boars and can also improve the heat stress resistance of boars[5]. In order to improve the welfare level of breeding boars， it is recommended to feed some green fodder （feed 2.0-2.5 kg/d） except for the complete feed， but must ensure that the feed is clean， non-toxic and pesticide free. Enclosure environment
Ambient temperature
Temperature is an important environmental factor in pigsty and has an important effect on growth and reproductive performance. The sweat glands of pigs are not developed， the individuals breeding boars are relatively large， the subcutaneous fat is thick， and it is not easy to dissipate heat. During the high temperature season， the male boars showed decreased sexual desire， lower semen quality， lower effective sperm count， lower sperm motility， thinner density and higher deformity rate. When the temperature reaches or exceeds 30 ℃， heat stress will affect spermatogenesis， and ejaculation and sperm quantity will be decreased. Heat stress can also change the blood biochemical indexes and reduce the semen quality of boars， thus seriously affecting the performance of breeding boars[6]. To prevent heat stress in boars in summer， the main thing is to control the indoor temperature. It is suggested that some green feed should be fed in summer. Green feed not only has a positive effect on the semen quality of boars， but also improves the ability of heat stress resistance of boars[5].
Light
Two studies in Germany and Canada on the effects of light exposure on boars found that plasma testosterone levels in boars were the lowest in July and August， and highest in October to December， when light gradually shortened. The highest amount of sperm per ejaculation occurs in winter. Since testosterone directly affects the development and action of spermatogenic and accessory sexual gland in boars， the intensity and length of light in different seasons may affect the number of effective spermatozoa obtained from spermatogenesis in boars[7]. Most studies have shown that the most suitable illumination time for adult boars is 8 to 10 h per day[8-11]. Proper prolongation of light can promote gonadal development and early sexual maturation in piglets[9， 11-12]. Some researchers extended the exposure from 20 weeks to 26 weeks of age， and 73 % boars were able to gather semen， compared with 26 % in the natural light group[9， 12-13]. More attention should be paid to the effect of light on the reproductive performance of pigs. In spring and summer， the light time was reduced to 8-10 h per day （100-150 lux）， which can greatly improve the reproductive performance of adult boars. The standard of our country stipulates that the pig farm should provide at least 8 h of continuous illumination and at least 6 h of continuous darkness every 24 h for pigs fed in the house. Exercise
Current factory farming makes pigs lack of exercise and is put back to rest after gathering spermatozoa every day. It is easy to make boars too fat， sexual desire weakened， and semen quality decline or even lose breeding ability. Exercise plays an important role in boar semen quality， so we should ensure that boars can exercise every day. Pig farms should build an appropriate sports field meeting the epidemic prevention requirement according to the scale of farming， insist on driving boars exercise， to ensure the exercise of boars （exercise 1-2 times a day， use slow-fast-slow exercise mode to make boars breathe a little fast or wheeze）， so as to maintain their vigorous sperm supply ability. In addition， the boar testis should be massaged for 10 to 15 min during the day， and the boar body should be brushed and swabbed （it can promote blood circulation， prevent and cure parasitic diseases， make human pigs compatible and so on）， so as to improve the welfare level of boars.
Artificial semen collection
According to the rule of spermatogenesis， the interval between collection of spermatozoa should not be less than 3 d[13]. The quality of the semen was poor at the age of less than 9 months and was the best when the boar was 2-3 years old. Avoid premature and overuse which could lead to premature ageing of boars. Generally， spermatozoa were collected at the following frequency： once a week at the age of 12 to 16 months during the training period， 2-3 times a week at the age of 1-2 years， 4-5 times a week at the age of 4-5 years and one time a day in the busy season of spermatozoa， no more than twice a day and one day off every week when used continuously， and once every 1-2 d over 5 years of age[14]. Exceptional boars may develop vice due to improper training （such as self-indulgence， bite sows and attack operators， etc.）. Be patient， brush the pig body every day， massage the testicles. In the collection of sperm， people should take a meek attitude， and cannot shout loudly， intimidation and whipping[15].
Sexual behavior
Sexual behavior is a series of special behaviors of both sexes in direct contact. Sexual behavior of boars includes sexual excitement and courtship， erection， mating， ejaculation， etc. Nature expression is one of the five basic welfare of animals. For breeding boars， sexual behavior （i.e.， sexual welfare of pigs） is an important part of the animal welfare of boars. In the process of artificial insemination， spermatogenesis and insemination have replaced the courtship and mating between males and females， resulting in the loss of sexual behavior and the loss of sexual welfare in pigs. At present， due to the development of artificial insemination technology， the sexual behavior of boars is basically missing or partially missing. Boars are only used for estrus induction， estrus identification and pregnancy identification in sows. At the time of insemination， there were boars beside them， which retained sexual behaviors such as courtship and lost mating and other sexual behaviors. Natural mating should be properly preserved. Environment enrichment
Environment enrichment is an effective way to improve the behavior， physiology and psychology of captive animals. It can increase the complexity of animals daily life and make animals behave naturally and reduce the incidence of stereotypical or other abnormal behavior[16]. The essence of environmental enrichment is to improve the welfare of captive animals by changing their living environment so that they can exhibit as much natural behavior as possible[17]. Enriched environment can relieve the stress of animals[18-20]. Cushions， toys and music are important means or measures for environmental enrichment. At present， due to the lack of general awareness of animal welfare， very few welfare facilities are added to the stall or pen， resulting in a monotonous and barren living environment for pigs. The low concentration of environment makes many normal behaviors （inquiry， nesting， etc.） unexpressed and shows more abnormal behaviors （such as empty chewing， hurdle biting， fighting， etc.）
Padding & ground
The advantage of padding is that it cannot only give pigs dry comfort， better protect hoof health， but also satisfy their natural bite and other inquiry behavior. The pad can not only give the pig dry comfortable feeling， better protect the hoof health， but also satisfy its natural inquiry behavior such as gnawing. In many European countries， it is legally compulsory to provide mat grass to pigs at all stages. It is evident how important it is to the welfare and health of pigs[3]. However， due to the cost （labor supply， replacement and purchase cost）， and the difficulty of handling after the use of mat grass， the boars in our country generally cannot enjoy the benefits of padding. It is recommended that the clean and soft mats should often be provided. In addition， the floor of boar shed cannot be too smooth， and in order to prevent the boar from falling down and causing mechanical hoof injury， the hoof can be well protected by providing padding material.
Toys
Animals have a complex nervous system， the ability to sense pain and happiness， is a form of life with emotions， emotions such as delightedness， angry， grief， joyfulness， sadness， fear and disappointment， as well as physical and mental pain[21]. Play is the nature of an animal， and toys are one of the objects in which animals express their nature. Toys can increase the expression of natural behaviors such as chewing， biting， grinding and playing in pigs[22]. In the UK， pig farmers must ensure that their pigs have toys， or face a penalty of ￡1 000 or three months in prison[23]. European Union countries also have similar animal welfare regulations. In 2014， China issued "Farm Animal Welfare Requirements： Pigs"[4]， in which about pigs toys are only generally recommended to reduce the incidence of abnormal behavior in pigs. Pig farms should provide the necessary materials to meet the requirements of environmental enrichment. There is no clear rule as to whether or not to provide toys to pigs. In addition， the research and application of pig toys in China is less. The pig farm should provide welfare toys such as iron chain， rubber ball or plastic ball to the boar to increase the exercise of the boar and reduce the lying down behavior of the pig and at the same time improve the welfare level of the boar. Music
Music can affect the emotions of animals， and it also affects the immune function， learning and memory ability of animals， and the structure and function of the nervous system of animals[24]. The therapeutic effect of music in the field of human medicine has been affirmed and has a good effect. Music has been widely used in the treatment and rehabilitation of various diseases of human being[25]. The hearing range of swine is similar to that of humans， but it is slightly higher than that of people. The frequency range that pigs can hear is between 42 Hz and 40.5 kHz. Optimal sensitivity region： 250 Hz-16 kHz[26]. The suitable music has some positive effects on the growth and development of boars， reproduction and inhibition of adverse stress reactions. Playing music can significantly improve stress[27-28]. soothing low volume music can reduce stress， improve productivity， and promote growth and development[29]. It is recommended that pig farms regularly play soothing low volume music to improve the welfare of boars.
Other aspects
Mature boars are large and powerful， so be careful when herding， treating， or collecting samples. Tusks must be cut off （keep 1.2 cm above） by wire saws regularly. To treat adult boars carefully， attention usually should be paid to boar body temperature and appetite. Rectal temperature of boars which lost appetite or has clinical symptoms， must be measured， and if the temperature is greater than 40 degrees Celsius， collection of spermatozoa should be stopped and the veterinarian should immediately have informed to begin the diagnosis immediately. In addition， euthanasia of breeding boar is carried out in most European Union and other countries at present， but there is no specific regulation on this aspect in our country at present.
Brief Summary
The improvement of animal welfare level is not only the improvement of the management level of modern aquaculture industry， but also the concrete embodiment of the improvement of human civilization. Pig farms should strive to improve the welfare level of boars in order to better fulfill the task of supplying and breeding sows and ensure the production and efficiency of the whole pig farm. The improvement of boar welfare benefits not only the boar itself， but also the whole farm and other farmers.
References
[1] LI DG， CHEN F. Welfare problem and good agricultural practice at various main stages of live pig[J]. Swine Production， 2009 （5）： 46-48. [2] YUN GB. Effect of farrowing pen raising on boar[C]//Proceedings of the "Liuma" cup genetic improvement of live pigs and nationwide seminar of key techniques of artificial pig insemination， Zhangjiajie： Beijing Animal Husbandry and Veterinary General Station， 2011： 353-354
[3] WANG XQ. Simple analysis of several problems about the concept and practice of welfare pig raising[J]. Swine Production， 2015 （1）： 81-86.
[4] China Association for Standardization. Farm Animal Welfare Requirements： Pigs[S]. Beijing： China Association for Standardization， 2014.
[5] YAN XC. Main measures for preventing heat stress on service boar[J]. Agricultural Technology & Equipment， 2013 （11）： 34-35.
[6] ZHANG L， LIU ZH， SONG DJ. Effect of heat stress on semen quality and serum index in boar[J]. Livestock and Poultry Industry， 2008 （9）： 18-20.
[7] YAN ZC. Effects of air temperature and illumination on reproductive rate of boar[J]. Swine Industry Science， 2009， 26（7）： 74-77.
[8] YANG MS. Illumination with reproductive performance of boar[J]. Modern Animal Husbandry， 1996， （6）： 7-8.
[9] MIAO YT， LI GD， WANG JC， et al. Effect of illumination on reproductive performance of swine[J]. North Animal Husbandry， 2014 （24）： 21.
[10] GUAN YF. Effect of illumination on swine production[J]. Modern Animal Husbandry Science & Technology， 2016 （3）： 17.
[11] LIU CD， YANG L， PU HZ， et al. Effect of illumination on swine growth and reproductive performance[J]. Swine Industry Science， 2016 （10）： 94-96.
[12] LIU JH， SHI MW， CAO GW. Effect of illumination on reproductive performance of swine[J]. Jilin Animal Husbandry and Veterinary Medicine， 2016， 37（8）： 25-26.
[13] GAO YC， SHEN WL. Several aspects of rational application of service boar[J]. Technical Advisor for Animal Husbandry， 2012 （6）： 17.
[14] WEN SY. Healthful aquaculture and efficient utilization of service boar of large-scale pig farm[J]. Swine Industry Outlook， 2013 （10）： 10-14.
[15] BAI SS， ZHANG L， HUANG JT， et al. Several factors and improvement measures of short utilization period service boar[J]. Livestock and Poultry Industry， 2014 （5）： 45.
[16] ZHANG YZ. Scientific research status and development prospect of environmental enrichment of Chinese zoos[J]. Mod Agric Sci Technol， 2014 （22）： 243-246.
[17] NEWBERRY RC. Environmental enrichment： Increasing the biological relevance of captive environments[J]. Applied Animal Behaviour Science， 1995， 44（2-4）： 229-243. [18] GEVERINK NA， JONG I CD， LAMBOOIJ E， et al. Influence of housing conditions on responses of pigs to preslaughter treatment and consequences for meat quality[J]. Canadian Journal of Animal Science， 1999， 79（3）： 285-291.
[19] DE JONG IC， PRELLE IT， VAN DE BURGWAL JA， et al. Effects of environmental enrichment on behavioral responses to novelty， learning， and memory， and the circadian rhythm in cortisol in growing pigs[J]. Physiology & Behavior， 2000， 68（4）： 571-578.
[20] KLONT RE， HULSEGGE B， HOVINGBOLINK AH， et al. Relationships between behavioral and meat quality characteristics of pigs raised under barren and enriched housing conditions[J]. Journal of Animal Science， 2001， 79（11）： 2835-2843.
[21] YUN SF. Ensure experimental animal welfare， promoting development of life sciences： Brief talk about experimental animal welfare problems[J]. Chinese Journal of Comparative Medicine， 2015 （3）： 90.
[22] ZHANG T， ZHANG X， GUO YS， et al. study on the application of three kinds of animal welfare toys for swine in production[J]. Swine Industry Science， 2016， 33（8）： 51-53.
[23] WANG XQ. Pig breeder will get a packet if not providing toys for porkers[J]. Swine Production， 2007 （6）： 4.
[24] LI J， WANG SD. Animal experimental study on musical treatment effect[J]. Sichuan Journal of Zoology， 2007， 26（1）： 196-197.
[25] ZHANG J， XU CT. Musical treatment mechanism and it application and research status[J]. Journal of Xinxiang Medical College， 2011， 28（6）： 788-791.
[26] HEFFNER RS， HEFFNER HE. Hearing in domestic pigs （Sus scrofa） and goats （Capra hircus）[J]. Hearing Research， 1990， 48（3）： 231-240.
[27] GU XH. Swine welfare cultivation and research progress[J]. China Swine Industry， 2013， 8（11）： 17-20.
[28] ZHOU LZ， CAO YC， MIU HM， et al. Effect of music on serum enzyme activity of dairy cattle under heat stress[J]. Progress In Veterinary Medicine， 2009， 30（3）： 47-49.
[29] PAN JQ， TIAN YB， HUANG YM， et al. Research progress of the effect of music environment on animal[C]//Proceedings of national convention of animal physiology and biochemistry， Shenyang： China Animal Husbandry and Veterinary Association， 2014：88-89.
Key words Animal welfare； Boar welfare； China
With the rapid development of swine industry， intensive and scale is gradually replacing the extensive and scattered farming model. Scale farming can increase productivity but is likely to harm the welfare of pigs. Animal husbandry developed countries attach great importance to the welfare of animals， but many pig farms in China， including some large farms， do not pay enough attention to animal welfare. Breeding boar is the core of modern pig farm， which is responsible for the reproductive task of supplying sperm for sows， and its quality has an important influence on the whole pig farm. With the development of artificial insemination， breeding boar plays an increasingly important role in pig production and the welfare of it is becoming more and more important. The present raising management methods should be improved to enhance the welfare level of pigs according to its physiological and psychological demands， so as to achieve the win-win situation between human beings and animals.
About Animal Welfare
So far， there is no precise definition of animal welfare. But it is generally understood that animals enjoy the five freedoms （Freedom from hunger and thirst； Freedom from discomfort； Freedom from pain， injury or disease； Freedom to express normal behavior； Freedom from fear and distress）. At present， there are still some people who do not accepted or recognize animal welfare， think that animals should not enjoy welfare. Some people advocate that animals should be equal to human beings and that animals should be totally banned even from conducting scientific experiments and that animal product should not be used by human beings. The welfare of pigs is closely related to human interests. Welfare of Breeding Boars in China
Rearing mode
Adult boars are raised in a single pen and kept away from sows in order to be in a quiet state and reduce interference， fight and hip climbing. Boars are usually kept in captivity alone， but if boars grow up together and have plenty of room to avoid fighting， they can be farmed in groups[1]. At present， for the convenience of management and cost saving， some pig farms in our country also use individual stall system for breeding boars， sometimes close to sows， or even placed in the same shed. There were no significant changes in sperm yield， sperm density and sperm motility in boars， but there were significant increase in leg and hoof injury and decrease of sexual desire after 16 months of use in boars[2]， which resulted in high rejection rate of breeding boars （generally used for less than 18 months， sperm motility could not meet the requirements and had to be eliminated）. Individual stall system is introduced from the West， mainly used for pregnant sows. It limits the free movement of pigs， and causes a series of problems， such as the long-term hog hanging in the limit column， rigid behavior， decreased cardiopulmonary function， foot and limb disease and increased mastitis and so on， and abnormal rejection rate is over 13%[3]. The limit bar not only damages the welfare of boar， but also shortens the utilization time of breeding boar. EU countries， New Zealand， Australia and other developed countries have banned or partially banned the use of individual stall， China has not banned the system. Our country stipulates that the boar pen should be allowed to turn around freely， with a minimum total area of not less than 7.5 m2/head， and a mating fence area of not less than 12 m2， so as to ensure sufficient space for courtship and mating[4]. Do not use the normal pregnancy individual stall to raise breeding boars，but use larger boar pen.
Feed
Pigs are vegetarian omnivorous animals whose ancestors feed on wild herbs and root tubers. The modern factory cultivation mode has deprived the pig of the taste of the green feed， so that it can eat complete feed for the whole life and can hardly eat green feed. Green feed can not only provide natural vitamins to pigs， but also provide dietary cellulose， which can effectively prevent constipation and play an active role in maintaining intestinal microbial balance. In addition， green feed can also increase the feeling of fullness. The multivitamins contained in green feed have a positive effect on the semen quality of boars and can also improve the heat stress resistance of boars[5]. In order to improve the welfare level of breeding boars， it is recommended to feed some green fodder （feed 2.0-2.5 kg/d） except for the complete feed， but must ensure that the feed is clean， non-toxic and pesticide free. Enclosure environment
Ambient temperature
Temperature is an important environmental factor in pigsty and has an important effect on growth and reproductive performance. The sweat glands of pigs are not developed， the individuals breeding boars are relatively large， the subcutaneous fat is thick， and it is not easy to dissipate heat. During the high temperature season， the male boars showed decreased sexual desire， lower semen quality， lower effective sperm count， lower sperm motility， thinner density and higher deformity rate. When the temperature reaches or exceeds 30 ℃， heat stress will affect spermatogenesis， and ejaculation and sperm quantity will be decreased. Heat stress can also change the blood biochemical indexes and reduce the semen quality of boars， thus seriously affecting the performance of breeding boars[6]. To prevent heat stress in boars in summer， the main thing is to control the indoor temperature. It is suggested that some green feed should be fed in summer. Green feed not only has a positive effect on the semen quality of boars， but also improves the ability of heat stress resistance of boars[5].
Light
Two studies in Germany and Canada on the effects of light exposure on boars found that plasma testosterone levels in boars were the lowest in July and August， and highest in October to December， when light gradually shortened. The highest amount of sperm per ejaculation occurs in winter. Since testosterone directly affects the development and action of spermatogenic and accessory sexual gland in boars， the intensity and length of light in different seasons may affect the number of effective spermatozoa obtained from spermatogenesis in boars[7]. Most studies have shown that the most suitable illumination time for adult boars is 8 to 10 h per day[8-11]. Proper prolongation of light can promote gonadal development and early sexual maturation in piglets[9， 11-12]. Some researchers extended the exposure from 20 weeks to 26 weeks of age， and 73 % boars were able to gather semen， compared with 26 % in the natural light group[9， 12-13]. More attention should be paid to the effect of light on the reproductive performance of pigs. In spring and summer， the light time was reduced to 8-10 h per day （100-150 lux）， which can greatly improve the reproductive performance of adult boars. The standard of our country stipulates that the pig farm should provide at least 8 h of continuous illumination and at least 6 h of continuous darkness every 24 h for pigs fed in the house. Exercise
Current factory farming makes pigs lack of exercise and is put back to rest after gathering spermatozoa every day. It is easy to make boars too fat， sexual desire weakened， and semen quality decline or even lose breeding ability. Exercise plays an important role in boar semen quality， so we should ensure that boars can exercise every day. Pig farms should build an appropriate sports field meeting the epidemic prevention requirement according to the scale of farming， insist on driving boars exercise， to ensure the exercise of boars （exercise 1-2 times a day， use slow-fast-slow exercise mode to make boars breathe a little fast or wheeze）， so as to maintain their vigorous sperm supply ability. In addition， the boar testis should be massaged for 10 to 15 min during the day， and the boar body should be brushed and swabbed （it can promote blood circulation， prevent and cure parasitic diseases， make human pigs compatible and so on）， so as to improve the welfare level of boars.
Artificial semen collection
According to the rule of spermatogenesis， the interval between collection of spermatozoa should not be less than 3 d[13]. The quality of the semen was poor at the age of less than 9 months and was the best when the boar was 2-3 years old. Avoid premature and overuse which could lead to premature ageing of boars. Generally， spermatozoa were collected at the following frequency： once a week at the age of 12 to 16 months during the training period， 2-3 times a week at the age of 1-2 years， 4-5 times a week at the age of 4-5 years and one time a day in the busy season of spermatozoa， no more than twice a day and one day off every week when used continuously， and once every 1-2 d over 5 years of age[14]. Exceptional boars may develop vice due to improper training （such as self-indulgence， bite sows and attack operators， etc.）. Be patient， brush the pig body every day， massage the testicles. In the collection of sperm， people should take a meek attitude， and cannot shout loudly， intimidation and whipping[15].
Sexual behavior
Sexual behavior is a series of special behaviors of both sexes in direct contact. Sexual behavior of boars includes sexual excitement and courtship， erection， mating， ejaculation， etc. Nature expression is one of the five basic welfare of animals. For breeding boars， sexual behavior （i.e.， sexual welfare of pigs） is an important part of the animal welfare of boars. In the process of artificial insemination， spermatogenesis and insemination have replaced the courtship and mating between males and females， resulting in the loss of sexual behavior and the loss of sexual welfare in pigs. At present， due to the development of artificial insemination technology， the sexual behavior of boars is basically missing or partially missing. Boars are only used for estrus induction， estrus identification and pregnancy identification in sows. At the time of insemination， there were boars beside them， which retained sexual behaviors such as courtship and lost mating and other sexual behaviors. Natural mating should be properly preserved. Environment enrichment
Environment enrichment is an effective way to improve the behavior， physiology and psychology of captive animals. It can increase the complexity of animals daily life and make animals behave naturally and reduce the incidence of stereotypical or other abnormal behavior[16]. The essence of environmental enrichment is to improve the welfare of captive animals by changing their living environment so that they can exhibit as much natural behavior as possible[17]. Enriched environment can relieve the stress of animals[18-20]. Cushions， toys and music are important means or measures for environmental enrichment. At present， due to the lack of general awareness of animal welfare， very few welfare facilities are added to the stall or pen， resulting in a monotonous and barren living environment for pigs. The low concentration of environment makes many normal behaviors （inquiry， nesting， etc.） unexpressed and shows more abnormal behaviors （such as empty chewing， hurdle biting， fighting， etc.）
Padding & ground
The advantage of padding is that it cannot only give pigs dry comfort， better protect hoof health， but also satisfy their natural bite and other inquiry behavior. The pad can not only give the pig dry comfortable feeling， better protect the hoof health， but also satisfy its natural inquiry behavior such as gnawing. In many European countries， it is legally compulsory to provide mat grass to pigs at all stages. It is evident how important it is to the welfare and health of pigs[3]. However， due to the cost （labor supply， replacement and purchase cost）， and the difficulty of handling after the use of mat grass， the boars in our country generally cannot enjoy the benefits of padding. It is recommended that the clean and soft mats should often be provided. In addition， the floor of boar shed cannot be too smooth， and in order to prevent the boar from falling down and causing mechanical hoof injury， the hoof can be well protected by providing padding material.
Toys
Animals have a complex nervous system， the ability to sense pain and happiness， is a form of life with emotions， emotions such as delightedness， angry， grief， joyfulness， sadness， fear and disappointment， as well as physical and mental pain[21]. Play is the nature of an animal， and toys are one of the objects in which animals express their nature. Toys can increase the expression of natural behaviors such as chewing， biting， grinding and playing in pigs[22]. In the UK， pig farmers must ensure that their pigs have toys， or face a penalty of ￡1 000 or three months in prison[23]. European Union countries also have similar animal welfare regulations. In 2014， China issued "Farm Animal Welfare Requirements： Pigs"[4]， in which about pigs toys are only generally recommended to reduce the incidence of abnormal behavior in pigs. Pig farms should provide the necessary materials to meet the requirements of environmental enrichment. There is no clear rule as to whether or not to provide toys to pigs. In addition， the research and application of pig toys in China is less. The pig farm should provide welfare toys such as iron chain， rubber ball or plastic ball to the boar to increase the exercise of the boar and reduce the lying down behavior of the pig and at the same time improve the welfare level of the boar. Music
Music can affect the emotions of animals， and it also affects the immune function， learning and memory ability of animals， and the structure and function of the nervous system of animals[24]. The therapeutic effect of music in the field of human medicine has been affirmed and has a good effect. Music has been widely used in the treatment and rehabilitation of various diseases of human being[25]. The hearing range of swine is similar to that of humans， but it is slightly higher than that of people. The frequency range that pigs can hear is between 42 Hz and 40.5 kHz. Optimal sensitivity region： 250 Hz-16 kHz[26]. The suitable music has some positive effects on the growth and development of boars， reproduction and inhibition of adverse stress reactions. Playing music can significantly improve stress[27-28]. soothing low volume music can reduce stress， improve productivity， and promote growth and development[29]. It is recommended that pig farms regularly play soothing low volume music to improve the welfare of boars.
Other aspects
Mature boars are large and powerful， so be careful when herding， treating， or collecting samples. Tusks must be cut off （keep 1.2 cm above） by wire saws regularly. To treat adult boars carefully， attention usually should be paid to boar body temperature and appetite. Rectal temperature of boars which lost appetite or has clinical symptoms， must be measured， and if the temperature is greater than 40 degrees Celsius， collection of spermatozoa should be stopped and the veterinarian should immediately have informed to begin the diagnosis immediately. In addition， euthanasia of breeding boar is carried out in most European Union and other countries at present， but there is no specific regulation on this aspect in our country at present.
Brief Summary
The improvement of animal welfare level is not only the improvement of the management level of modern aquaculture industry， but also the concrete embodiment of the improvement of human civilization. Pig farms should strive to improve the welfare level of boars in order to better fulfill the task of supplying and breeding sows and ensure the production and efficiency of the whole pig farm. The improvement of boar welfare benefits not only the boar itself， but also the whole farm and other farmers.
References
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